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Investigating the neural basis of spontaneous thought with fMRI and mindfulness meditation Ellamil, Melissa Marie 2014

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 INVESTIGATING THE NEURAL BASIS OF SPONTANEOUS THOUGHT WITH FMRI AND MINDFULNESS MEDITATION  by  MELISSA MARIE ELLAMIL  Hon.B.Sc., The University of Toronto, 2008 M.A., The University of British Columbia, 2010   A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY  in  The Faculty of Graduate and Postdoctoral Studies  (Psychology)   THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  December 2014  © Melissa Marie Ellamil, 2014 ii  ABSTRACT One of the most intriguing yet least understood aspects of the human mind is its tendency to give rise to spontaneous, undirected mental processes – thoughts that occur and proceed without our deliberate effort or control. The present dissertation examined the neural basis of spontaneous thought by integrating first-person reports from individuals with extensive introspective training (i.e., mindfulness meditators) with third-person neural measures from fMRI experience sampling procedures. In Experiment 1, time courses of brain activation during self-caught spontaneous thought events revealed that the medial temporal lobe (MTL) was recruited first, suggesting it may be central to the initial generation of spontaneous thoughts. The medial prefrontal cortex (MPFC) showed recruitment next, suggesting it may be important for the subsequent affective elaboration of spontaneous thoughts. The lateral prefrontal cortex (LPFC) showed recruitment last, suggesting it may contribute to further metacognitive evaluation and monitoring of spontaneous thoughts. In Experiment 2, spontaneous thought elaboration events (i.e., when a second thought followed an initial thought) showed increased MPFC activation and decreased MTL activation. Spontaneous thought elaboration may thus engage affective evaluation processes while suppressing associative generation processes. In Experiment 3, spontaneous thoughts reported during high MTL activity (as determined by real-time fMRI software) were associated with meaning-making content such as remembering, planning, and linking concepts. In contrast, spontaneous thoughts reported during low MTL activity were associated with present-centered content such as body sensations, emotions, awareness, and concentration. The level of MTL activation may thus reflect different qualities, but not necessarily different quantities, of spontaneous thought. First-person, introspective information about the timing, sequence, and content of spontaneous thoughts collected in the iii  present experiments helps to refine current accounts of how brain regions consistently implicated in spontaneous thought specifically contribute to its component processes. The present dissertation reflects a step toward expanding the role of first-person, introspective reports in neuroscience in order to enhance our understanding of the full spectrum of human thought. iv  PREFACE I prepared the content of this dissertation with minor edits from Kalina Christoff. None of the text of the dissertation was taken directly from previously published or collaborative articles. The research presented in Chapters 2, 3, and 4 was primarily conducted by myself. I was responsible for study conception, design and programming; data collection, analysis and interpretation; and manuscript composition. Sean Pritchard was primarily responsible for participant recruitment and was consulted on the study design. Evan Thompson assisted with study conception and design. Graeme McCaig was responsible for programming the real-time fMRI software used in Chapter 4. Kalina Christoff assisted with study conception and design, data interpretation, and critical review of the dissertation. The experiments were approved by the University of British Columbia’s Research Ethics Board, HO8-00153: Meditation (Chapters 2 and 3) and H06-03324: Real-time (Chapter 4). v  TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii PREFACE ...................................................................................................................................... iv TABLE OF CONTENTS ................................................................................................................ v LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ........................................................................................................................ x ACKNOWLEGEMENTS .............................................................................................................. xi DEDICATION .............................................................................................................................. xii CHAPTER 1 – INTRODUCTION ................................................................................................. 1 Challenges in spontaneous thought research ...................................................................... 1 Examining the onset and development of spontaneous thought ............................. 1 Introspective observation of spontaneous thought .................................................. 3 Neural correlates of spontaneous thought ........................................................................... 4 Spontaneous thought and the default network ........................................................ 4 Spontaneous thought beyond the default network .................................................. 6 Outstanding questions ............................................................................................. 8 Overview of dissertation ..................................................................................................... 9 Experiment 1 – Spontaneous thought generation ................................................. 10 Experiment 2 – Spontaneous thought elaboration ................................................ 10 Experiment 3 – Real-time fMRI experience sampling ......................................... 11 CHAPTER 2 – EXPERIMENT 1: SPONTANEOUS THOUGHT GENERATION ................... 13 Methods............................................................................................................................. 14 Subjects ................................................................................................................. 14 Procedure .............................................................................................................. 15 vi  Stimuli ................................................................................................................... 19 fMRI data acquisition ........................................................................................... 20 fMRI data analysis ................................................................................................ 20 Time course extraction .......................................................................................... 22 Network analysis ................................................................................................... 22 Results ............................................................................................................................... 23 Behavioral results.................................................................................................. 23 SPM results ........................................................................................................... 24 Time course results ............................................................................................... 30 ST-PLS results ...................................................................................................... 32 Discussion ......................................................................................................................... 39 Neural correlates of spontaneous thought ............................................................. 39 Order of neural recruitment during spontaneous thought ..................................... 40 Generative subsystem of a spontaneous thought network .................................... 42 Elaborative subsystem of a spontaneous thought network ................................... 43 CHAPTER 3 – EXPERIMENT 2: SPONTANEOUS THOUGHT ELABORATION ................ 45 Methods............................................................................................................................. 46 Subjects ................................................................................................................. 46 Procedure .............................................................................................................. 47 Stimuli ................................................................................................................... 50 fMRI data acquisition ........................................................................................... 50 fMRI data analysis ................................................................................................ 50 Time course extraction .......................................................................................... 51 Network analysis ................................................................................................... 51 vii  Results ............................................................................................................................... 52 Behavioral results.................................................................................................. 52 SPM results ........................................................................................................... 52 Time course results ............................................................................................... 57 ST-PLS results ...................................................................................................... 59 Discussion ......................................................................................................................... 64 Elaborative processing in the MPFC .................................................................... 64 Metacognitive processing in the LPFC ................................................................. 65 Suppression of generative processing in the MTL ............................................... 66 Intermediary spontaneous thought processes........................................................ 67 CHAPTER 4 – EXPERIMENT 3: REAL-TIME FMRI EXPERIENCE SAMPLING ................ 70 Methods............................................................................................................................. 71 Subjects ................................................................................................................. 71 Real-time fMRI data acquisition ........................................................................... 72 Task procedure ...................................................................................................... 72 Real-time fMRI procedure .................................................................................... 73 Offline fMRI data analysis.................................................................................... 76 Results ............................................................................................................................... 76 Behavioral results.................................................................................................. 76 SPM results ........................................................................................................... 83 Discussion ......................................................................................................................... 89 Meaning-making and present-centered spontaneous thought processes .............. 89 Thought probe thresholds ..................................................................................... 91 Region of interest definitions ................................................................................ 92 viii  Subject-specified response categories................................................................... 92 CHAPTER 5 – GENERAL DISCUSSION .................................................................................. 94 Summary of main findings................................................................................................ 94 Contributions and neuroscientific implications ................................................................ 95 Neural recruitment specific to spontaneous thought ............................................. 96 Sequence of neural processes during spontaneous thought .................................. 97 Neural contributions to component processes of spontaneous thought ................ 98 Suppression of generative processes by elaborative processes ............................. 99 Clinical and educational implications ............................................................................... 99 Psychiatric disorders ........................................................................................... 100 Creative thinking ................................................................................................. 101 Limitations ...................................................................................................................... 102 Future directions ............................................................................................................. 104 Conclusions ..................................................................................................................... 107 REFERENCES ........................................................................................................................... 108 APPENDICES ............................................................................................................................ 126 Appendix A: Meditation experience questionnaire ........................................................ 126 Appendix B: Task instructions........................................................................................ 128 Appendix C: Word lists .................................................................................................. 129 ix  LIST OF TABLES Table 2.1. Activation peaks for thought events (thought > word). ............................................. 27 Table 2.2. Activation peaks for word events (word > thought). ................................................. 29 Table 2.3. Whole-brain network clusters for thought events (thought > word). ......................... 35 Table 2.4. Whole-brain network clusters for word events (word > thought). ............................. 37 Table 3.1. Activation peaks for thought elaboration > thought dissolution. .............................. 55 Table 3.2. Activation peaks for thought dissolution > thought elaboration. .............................. 56 Table 3.3. Whole-brain network clusters for thought elaboration > thought dissolution. ......... 61 Table 3.4. Whole-brain network clusters for thought dissolution > thought elaboration. ......... 63 Table 4.1. Individual thought reports during high-activity and low-activity probes. .................. 79 Table 4.2. Activation peaks for thought events during high RAH activity................................. 86 Table 4.3. Activation peaks for thought events during low RAH activity. ................................. 88  x  LIST OF FIGURES Figure 2.1. Schematic of Experiment 1 task. .............................................................................. 18 Figure 2.2. Activation maps for thought and word events. ......................................................... 26 Figure 2.3. Time courses during thought and word events. ........................................................ 31 Figure 2.4. Whole-brain network maps for thought and word events. ........................................ 34 Figure 3.1. Schematic of Experiment 2 task. .............................................................................. 49 Figure 3.2. Activation maps for thought elaboration and thought dissolution events. ............... 54 Figure 3.3. Time courses during thought elaboration and thought dissolution events. .............. 58 Figure 3.4. Whole-brain network maps for thought elaboration and dissolution events. ........... 60 Figure 4.1. Real-time fMRI display viewed by the experimenter during scanning. ................... 75 Figure 4.2. Individual thought reports during high-activity and low-activity probes.................. 81 Figure 4.3. Averaged thought reports during high-activity and low-activity probes. ................. 82 Figure 4.4. Activation maps for thought events during high and low RAH activity. ................. 85  xi  ACKNOWLEGEMENTS Thank you to my supervisor, Kalina Christoff, for her expert guidance and collaboration on this dissertation. Thank you to Todd Handy and Colleen Brenner for being part of my supervisory committee and providing valuable feedback and support. Thank you to collaborators Sean Pritchard and Evan Thompson for their help with recruiting the participants and designing the experiments. Thank you to Graeme McCaig for programming the real-time fMRI software and to the UBC MRI Research Centre technicians for helping set up the real-time fMRI sessions. Thank you to the Natural Sciences and Engineering Research Council of Canada (NSERC Canada Graduate Scholarship) and the Mind and Life Institute (Francisco J. Varela Research Award) for supporting this research. Thank you to Matt Dixon, Kieran Fox, Rebecca Todd, and my friends from Green College and the Department of Psychology for the many valuable discussions and continual encouragement both in and out of the lab. Special thanks are owed to my parents and my partner for their constant love and support. xii  DEDICATION     Thoughts meander like a restless wind inside a letter box. They tumble blindly as they make their way across the universe. — John Lennon 1  CHAPTER 1 – INTRODUCTION One of the most intriguing yet least understood aspects of the human mind is its tendency to give rise to spontaneous, undirected mental processes – thoughts that occur and proceed without our deliberate effort or control. Psychological studies show that 96% of American adults report some kind of daydreaming each day (Singer & McCraven, 1961), at least 30% of people’s daily thoughts can be classified as mind wandering or thoughts unrelated to the current task (Kane et al., 2007; Killingsworth & Gilbert, 2010; Klinger & Cox, 1987), and as much as 50% of thoughts consist of daydreams or nonworking thoughts that are spontaneous and/or fanciful (Klinger, 2009). Spontaneous thought processes appear to be disrupted in a number of psychiatric disorders, such as depression (e.g., Giambra, Grodsky, Belongie, & Rosenberg, 1994), post-traumatic stress disorder (PTSD) (e.g., Berntsen & Rubin, 2008), and attention deficit/hyperactivity disorder (ADHD) (e.g., Smallwood, Fishman, & Schooler, 2007), but also seem to facilitate goal-directed cognitive processes, including memory consolidation (e.g., Ellenbogen et al., 2007), creative thinking (e.g., Baird et al., 2012), and decision making (e.g., Dijksterhuis, 2004). Given the ubiquity, clinical significance, and cognitive influences of spontaneous mental processes, it is important to increase our knowledge and understanding of how the brain supports this aspect of human thought.  Challenges in spontaneous thought research Examining the onset and development of spontaneous thought Spontaneous, undirected thoughts arise unintentionally or without volition and proceed with no conscious, deliberate effort to channel their course in a particular direction (Christoff, 2012). Although spontaneous thoughts tend to be unrelated to the current task (as in mind 2  wandering) and be decoupled from current sensory information (as in stimulus-independent thought) (Klinger, 2009), the distinguishing feature of spontaneous thoughts is that they occur unpredictably and uncontrollably. Their unpredictable and uncontrollable nature makes our well-developed, task-based methods of behavioral observation largely ineffective for investigating them. After all, it is impossible to control spontaneous thoughts or instruct subjects to have spontaneous thoughts. Consequently, in order to better understand spontaneous thought, we require alternative methods of examining its onset or initial generation and its development or subsequent progression. Such methods would likely rely more on subjects’ observations of their mental experiences and less on task-related performance measures as compared to traditional behavioral observation paradigms.  In addition, most neuroscientific investigations of spontaneous thought have used rest-based methods in which subjects were given no task or instructed to “do nothing” (Christoff, 2012). This “resting” state was assumed to result in conditions of low external perceptual and cognitive demands, which psychological studies have shown lead to an increased rate of spontaneous thoughts (Filler & Giambra, 1973; Giambra & Grodsky, 1989). Some studies collected retrospective self-reports regarding the frequency of spontaneous thoughts during a previous session of rest (e.g., D'Argembeau et al., 2005; Gorgolewski et al., 2014). Other studies administered questionnaires to determine subjects’ general tendencies to engage in spontaneous thoughts (e.g., Kucyi & Davis, 2014). However, subjects were usually not asked during the experimental sessions if and when spontaneous thoughts occurred, making it difficult to examine the neural processes associated with the onset of spontaneous thoughts. Several studies also employed experience sampling procedures, in which subjects were probed or asked about their spontaneous thoughts during rest at unpredictable intervals (e.g., Tusche, Smallwood, Bernhardt, 3  & Singer, 2014). However, only the presence and content of spontaneous thoughts were assessed but not the flow or development of those thoughts. Thus, although these experiments have provided a wealth of data about the possible neural correlates of spontaneous thought, they have not allowed direct assessment of neural recruitment during the onset or initial generation and during the development or subsequent progression of spontaneous thought. Introspective observation of spontaneous thought The present dissertation thus sought to use introspection, or the ongoing self-observation of one’s own mental state, to provide the first examination of the neural mechanisms that support the onset and development of spontaneous thought. To enable the collection of more accurate information about the onset and development of spontaneous thoughts, and hence more specific assessment of the sequence and contributions of neural processes during them, the present research recruited highly experienced mindfulness meditators. Mindfulness meditators are trained in the introspective observation of their mental experiences (Sayadaw, 1985, 2002). Training in this type of meditation has been associated with an enhanced ability to notice subtle and/or rapid events during vigilance (Jha, Krompinger, & Baime, 2007), attentional blink (Slagter et al., 2007; van Leeuwen, Muller, & Melloni, 2009), visual discrimination (MacLean et al., 2010), and auditory detection (Lutz et al., 2009) tasks. Mindfulness meditation training has also been associated with enhanced introspective awareness of body sensations, emotions, and cognitive processes (Fox et al., 2012; Garrison et al., 2013; Jo et al., 2014; Mirams, Poliakoff, Brown, & Lloyd, 2013; Nielsen & Kaszniak, 2006; Sze, Gyurak, Yuan, & Levenson, 2010). This evidence suggests that, compared to non-meditators, mindfulness meditators can detect the occurrence of more subtle mental events and can provide more detailed and accurate 4  introspective reports of their mental experiences. This makes mindfulness meditators highly valuable subjects for empirical investigations of spontaneous thought onset and development (Christoff, Cosmelli, Legrand, & Thompson, 2011). Therefore, the present dissertation employed a novel methodology that combined the highly developed skills of mindfulness meditators in introspectively observing their own spontaneous thought processes with the advantages of direct observation of neural processes offered by modern brain imaging methods. Neural correlates of spontaneous thought Neuroscientific research on spontaneous thought has revealed that low-cognitive demand situations, such as the absence of a task or performance of a highly practiced task, do not necessarily equate to an overall decrease or lack of mental activity. On the contrary, large areas of the brain have been shown to be consistently more active during rest conditions or easy tasks than during goal-directed and cognitively demanding tasks, likely reflecting the engagement of spontaneous mental processes during these periods. However, although there have been a number of brain regions and networks implicated in spontaneous thought, the default network has received the majority of neuroscientific attention compared to other networks, such as the medial temporal lobe memory structures or the executive network regions.    Spontaneous thought and the default network Neuroimaging studies have suggested that spontaneous thought is preferentially linked to activation in the default network of the brain, which includes, most prominently, the medial prefrontal cortex (MPFC), posterior cingulate cortex (PCC), and temporoparietal junction (TPJ) (Raichle et al., 2001). The default network is frequently engaged during the absence of a task (i.e., rest) or during easy, familiar tasks and thus tends to be regarded as reflecting passive or 5  task-negative mental states (Raichle et al., 2001). However, the default network also shows increased recruitment during goal-directed cognitive tasks that require the active self-generation of mental content. For example, retrieving autobiographical or episodic information, planning personal future events, and inferring the mental states of other individuals all recruit brain networks that greatly overlap with default network regions (Spreng & Grady, 2009; Spreng, Mar, & Kim, 2008). The specificity of default network recruitment to spontaneous mental processes thus remains unclear.        The default network has been theorized to act in opposition to the brain’s executive network, such that the “task-negative” default network becomes deactivated or actively suppressed when the “task-positive” executive network becomes activated, and vice versa (Fox et al., 2005; Greicius, Krasnow, Reiss, & Menon, 2003; Weissman, Roberts, Visscher, & Woldorff, 2006). However, more recent studies have found co-activation of these two networks during mind wandering (Christoff et al., 2009a), continuous film viewing (Golland et al., 2007), narrative speech comprehension (Wilson, Molnar-Szakacs, & Iacoboni, 2008), autobiographical planning (Spreng et al., 2010), and the evaluation of creative ideas (Ellamil, Dobson, Beeman, & Christoff, 2012). The co-activation of these two networks suggests that spontaneous thought may be part of a class of mental phenomena that allow executive network processes to occur without diminishing the contribution of the default network to enable highly complex, abstract, and integrated mental functions (Christoff et al., 2009a). However, how this interaction between the default and executive networks contributes to the content and flow of spontaneous thought has not yet been investigated. The default network has been proposed to integrate information from association cortices (e.g., sensory information) and memory regions (e.g., knowledge and rules) in order to represent 6  internally generated information (Bar, 2007; Binder et al., 1999; Buckner, Andrews-Hanna, & Schacter, 2008; Legrand & Ruby, 2009; Vogt & Laureys, 2005). This information is often affective and self-relevant in nature (Andrews-Hanna et al., 2010) but may also be related to others’ thoughts and intentions (i.e., mentalizing) (Spiers & Maguire, 2006). The TPJ may integrate inputs from multiple sensory and limbic regions, which may contribute to the reorienting of attention to salient self-generated information as well as theory of mind inferences (Decety & Lamm, 2007). The PCC may further integrate information from the association cortices (e.g., TPJ) and memory regions (e.g., medial temporal lobe, including the hippocampus and parahippocampus) and may serve as the interface between the MPFC and these regions by representing the relevant internally generated information (Buckner et al., 2008; Leech, Braga, & Sharp, 2012; Vogt & Laureys, 2005). The MPFC may perform inductive inferences based on internal affective information to draw conclusions that guide behavior. However, this series of neural processes and their proposed neural contributions have not yet been examined directly during spontaneous thought. Spontaneous thought beyond the default network  The relationship between spontaneous thought and the default network has primarily been based on studies that have examined just a few regions of interest (ROIs) in the default network – in particular the MPFC and PCC (Fox, Andrews-Hanna, Spreng, & Christoff, under review). However, analyses limited to a priori ROIs, in contrast to whole-brain analyses, mean that other brain regions that might contribute to spontaneous thought have been ignored. Indeed, the few studies of spontaneous thought that have employed whole-brain analyses regularly show recruitment of regions beyond the core default network (Fox et al., under review).  7  One of these regions is the medial temporal lobe (MTL) (Christoff, 2012), which includes the hippocampus (HPC) and parahippocampus (PHC) and is activated during the formation and retrieval of semantic and episodic associations (Bar, Aminoff, & Schacter, 2008; Henke et al., 1999; Rombouts et al., 1997). The MTL also shows activation during the generation of creative ideas (Ellamil et al., 2012) and mental simulations of past, future, and novel events that require the recombination of stored associations (Addis, Wong, & Schacter, 2007; Botzung, Denkova, & Manning, 2008; Hassabis, Kumaran, & Maguire, 2007; Okuda et al., 2003; Szpunar, Chan, & McDermott, 2009). This suggests that the MTL may be particularly important for the initial onset or generation of spontaneous thought.  Another region outside the default network that has been associated with spontaneous thought is the temporopolar cortex (TPC) (Christoff, 2012). The TPC is thought to integrate highly processed sensory data with interoceptive-autonomic information by binding complex perceptual input to visceral, emotional input from the anterior insula, amygdala, and MTL memory structures (Graham, Lee, Brett, & Patterson, 2003; Olson, Plotzker, & Ezzyat, 2007). This suggests that the TPC may contribute to the subsequent development or elaboration of spontaneous thought.  Although the executive network, which includes the dorsal anterior cingulate cortex (DACC) and dorsolateral prefrontal cortex (DLPFC), is often recruited during conditions that require high cognitive control (Desimone & Duncan, 1995; Miller & Cohen, 2001), it is also frequently recruited during neuroimaging studies of spontaneous thought (Christoff, 2012). The DACC has been proposed to support salience or conflict monitoring and detection processes that signal the need for increased cognitive control and facilitate attention focusing, attention shifting, and error detection (Carter, Botvinick, & Cohen, 1999; Carter et al., 1998). Meanwhile, the 8  DLPFC is thought to integrate and evaluate the relevance of inputs (defined in terms of current task rules and goals) from the DACC, other prefrontal areas, memory regions, and association cortices in order to implement the cognitive control required by a task (Carter & van Veen, 2007; Fleck, Daselaar, Dobbins, & Cabeza, 2006; MacDonald, Cohen, Stenger, & Carter, 2000).  The rostral LPFC (RLPFC) is also regularly activated in neuroimaging studies of spontaneous thought  (Christoff, 2012). Although not necessarily considered part of the executive network, the RLPFC has been proposed to integrate and evaluate the outputs of prior stages of cognitive processing from other prefrontal areas, contributing to cognitive control at high levels of abstraction (Christoff & Gabrieli, 2000; Christoff et al., 2009c; Petrides, 2005; Ramnani & Owen, 2004). This enables the RLPFC to facilitate complex cognitive processes such as relational reasoning (e.g., Christoff et al., 2001), multitasking (e.g., Braver & Bongiolatti, 2002), and moral decision making (e.g., Greene et al., 2004). The LPFC and DACC may thus contribute to the further development or elaboration of spontaneous thought through metacognitive, evaluative processing of thought content and processes. However, the proposed temporal dynamics and contributions of these regions outside the default network have not been assessed directly during spontaneous thought. Outstanding questions Although the aforementioned brain regions and networks all appear to play important roles in spontaneous thought, the temporal dynamics and distinct functional contributions of these neural processes during spontaneous thought flow remain unclear. In particular, the order of neural recruitment and the brain regions that are engaged during the initial generation of spontaneous thought had not yet been directly assessed, which Experiment 1 aimed to 9  investigate. The sequence of neural processes and the brain regions that are recruited during the subsequent elaboration of spontaneous thought had also not yet been examined, which Experiment 2 aimed to investigate. Finally, it remained to be investigated whether the occurrence and quality of spontaneous thought could be predicted by real-time activity fluctuations in a particular brain region, which was examined in Experiment 3. This would provide a more causal test of the link between the recruitment and dynamics of neural processes during spontaneous thought and their contributions to mental experience during spontaneous thought. By implementing a new method that not only collects online experiential information during fMRI scanning but also identifies and tracks spontaneous thoughts as they occur and progress, the present dissertation aimed to more directly examine the onset and development of spontaneous thought and, thus, the sequence of neural processes and the contributions of various brain regions during spontaneous thought. Overview of dissertation The research described here aimed to improve our understanding of the neural basis of spontaneous thought processes by integrating subjective reports from expert mindfulness meditators with objective neural measures from fMRI experience sampling procedures. Using the meditators’ enhanced ability to monitor the occurrence and progression of mental events, the present experiments collected information about the onset and development of spontaneous thoughts. This information enabled us to directly examine the temporal dynamics of brain activity and the distinct functional contributions of various brain regions and networks during spontaneous thought.  10  Experiment 1 – Spontaneous thought generation The first experiment aimed to examine neural recruitment during the initial generation of spontaneous thought content and the temporal dynamics of brain activity during spontaneous thought flow. In this study, instead of reporting on their thoughts at time points predetermined by the experimenter, the subjects reported with button presses whenever a thought arose and what type of thought it was. Compared to previous studies, this approach enabled a more precise detection of the onset of spontaneous thought and thus the brain regions engaged during the initial generation of spontaneous thought. Moreover, the ability to detect the temporal onset of spontaneous thought allowed the assessment of the sequence of neural processes during spontaneous thought flow. It was predicted that the occurrence of spontaneous thought would preferentially recruit MTL memory structures (HPC and PHC), default network regions (MPFC, PCC, and TPJ), and executive network areas (LPFC and DACC), consistent with previous research (Christoff et al., 2009b). In addition, it was predicted that the MTL would be recruited first and contribute to the initial generation of spontaneous thoughts. Moreover, it was predicted that default network regions would be engaged second and support the subsequent affective elaboration of spontaneous thoughts. Finally, it was predicted that executive network areas would be recruited last and contribute to the further metacognitive evaluation and monitoring of spontaneous thoughts.    Experiment 2 – Spontaneous thought elaboration Experiment 1, however, did not distinguish between initial, spontaneous, affective elaboration processes and subsequent, deliberate, metacognitive evaluation processes. Thus, in Experiment 2, subjects were instructed to press a button to indicate the occurrence or absence of 11  a second spontaneous thought after an initial spontaneous thought. This approach enabled the examination of neural recruitment specifically during spontaneous thought elaboration (i.e., when a second thought followed the initial thought) as well as during spontaneous thought dissolution (i.e., when no thought followed the initial thought). The spontaneous elaboration of thought was hypothesized to preferentially recruit default network regions, which include the MPFC, PCC, and TPJ. These structures appear to contribute to spontaneous, affective evaluations of inputs from memory regions, association cortices, and other prefrontal areas, which may result in the continuation of spontaneous thought flow. In addition, it was predicted that spontaneous thought dissolution would be associated with no change in activation in MTL memory structures and default network areas, which may reflect the return of generative and elaborative neural processes back to baseline levels of activation. Experiment 3 – Real-time fMRI experience sampling A third exploratory experiment aimed to examine whether the occurrence of spontaneous thought could be predicted by real-time fluctuations in the activation level of a particular brain region. In this study, real-time fMRI – in which data analysis occurs simultaneously with data acquisition (deCharms, 2007, 2008) – was used to deliver probes for spontaneous thought occurrence based on the level of activity in the right anterior hippocampus (RAH) instead of at random, predetermined time points. Compared to previous studies, this approach allowed the examination of whether activity in a certain brain region (e.g., RAH) is associated with a particular cognitive process (e.g., spontaneous thought), providing a more direct test of the causal link between brain recruitment and mental experience. The RAH has previously shown increased recruitment during the construction of mental simulations, especially about future 12  events, which form a large part of spontaneous thought content (e.g., Addis et al., 2009; Smallwood, Nind, & O’Connor, 2009; Weiler, Suchan, & Daum, 2010). Thus, it was predicted that probing during high levels of activity in the RAH would be associated with more reports of spontaneous thoughts compared to probing during low levels of activity in the RAH.  In summary, with the integration of first-person reports from highly experienced mindfulness meditators and third-person neural measures from fMRI experience sampling procedures, the present dissertation sought to examine the temporal dynamics of neural recruitment during the flow of spontaneous thought. An increased understanding of the temporal dynamics of neural recruitment during spontaneous thought could provide empirical support for and help to refine existing theories about how various brain regions and networks specifically contribute to the generation and elaboration of spontaneous thought. A more specific characterization of the contributions of various brain regions and networks to spontaneous thought could enhance our understanding of the dysfunctional and adaptive cognitive processes associated with spontaneous thought, as well as how they might be treated or enhanced.      13  CHAPTER 2 – EXPERIMENT 1: SPONTANEOUS THOUGHT GENERATION Spontaneous thought has been frequently associated with activation in a number of brain regions, including the default network (MPFC, PCC, and TPJ), MTL memory structures (HPC and PHC), TPC, RLPFC, and executive network (DLPFC and DACC) (Christoff, 2012). In most previous studies of spontaneous thought, however, subjects were not asked about their mental experience during the experiment and were assumed to have engaged in spontaneous thought during the resting state. Some studies relied on retrospective self-reports of spontaneous thought frequency during a previous session of rest (e.g., D'Argembeau et al., 2005; Gorgolewski et al., 2014). A few studies administered questionnaires to determine subjects’ general tendencies to engage in spontaneous thoughts (e.g., Kucyi & Davis, 2014). In other studies in which subjects were asked about their mental experience during rest, subjects reported on their thoughts at quasi-random, predetermined time points (e.g., Tusche et al., 2014). Consequently, the order in which brain regions and networks are recruited when spontaneous thoughts are initially generated remains unknown. Thus, Experiment 1 aimed to more directly assess the temporal dynamics of brain activity during spontaneous thought flow as well as neural recruitment during the generation of spontaneous thought by using mindfulness meditators’ enhanced ability to notice the occurrence of mental events (Hölzel et al., 2011; Lutz, Slagter, Dunne, & Davidson, 2008). In this experiment, subjects used button presses to report when thoughts arose and what type of thoughts they had. As a comparison condition, subjects also reported whenever words appeared onscreen and what type of words they were. The number and types of words presented matched the number and types of thoughts reported. This approach allowed a more specific examination of brain activation during spontaneous thought compared to a method that uses an uncontrolled, 14  “no thought” condition. This approach also enabled a more direct examination of neural recruitment during the initial generation of spontaneous thought compared to previous studies in which subjects reported their thoughts at predetermined time points.  MTL memory structures (HPC and PHC) have been associated with the formation and recombination of associations between incoming and stored pieces of information, which may form the basis of spontaneous thought content. Thus, the MTL was predicted to show preferential recruitment during initial spontaneous thought generation. In addition, if MTL memory structures contribute to the generation of spontaneous thought, these brain regions may be recruited first during spontaneous thought events. Furthermore, if default network areas (MPFC, PCC, and TPJ) contribute to the subsequent affective elaboration of the spontaneously generated thoughts, these brain regions may be engaged after. Finally, if executive network areas (LPFC and DACC) contribute to the further metacognitive evaluation and monitoring of spontaneous thoughts, these brain regions may be recruited last. Methods Subjects Eighteen subjects (after 4 exclusions; 8 male and 10 female; M = 49.91 years old, SD = 11.17, range = 29.39 – 68.42) participated in Experiment 1. The subjects were long-term, expert mindfulness meditators with more than 3,000 hours of lifetime meditation experience and at least 1 hour of daily practice in the Mahasi Vipassana tradition (M = 8,338.6 hours, SD = 5,989.98, range = 3,174 – 23,700). The number of hours reported did not include practice in other traditions (e.g., Zen meditation, Transcendental meditation, Goenka or body scanning meditation, Yoga, Tai Chi, Qi Gong). Eligibility screening consisted of the administration of a 15  meditation experience questionnaire (Appendix A) and a phone interview by collaborator and former Mahasi monk Sean Pritchard. The screening ensured consistency of the meditation technique across subjects and attainment of extensive knowledge of and experience with the meditation technique through regular practice and attendance of several long-term intensive retreats.  The subjects were recruited from Vipassana meditation communities in Vancouver (BC, Canada), Vancouver Island (BC, Canada), Boulder (CO, USA), San Francisco (CA, USA), and Seattle (WA, USA). All subjects had normal or corrected-to-normal vision with no MRI contraindications or current psychiatric medication use. Fourteen were right-handed and 4 were left-handed, but all used their right hand to respond during the experiment. Three subjects were excluded from the analyses due to excessive motion (2 with > 5° pitch rotation, and 1 with > 5° pitch rotation and > 5 mm in the z-direction). One subject was excluded from the analyses because the experiment software did not record his responses. All protocols were approved by the University of British Columbia (UBC; Vancouver, BC, Canada) Clinical Research Ethics Board and the UBC MRI Research Center. All subjects gave informed written consent prior to participating and received payment as compensation. Procedure One to two days prior to the actual scanning session, subjects engaged in a practice session identical to the actual scanning procedure in a mock scanner environment to become acclimatized to the task, button pressing, and scanner noises. Subjects alternated between monitoring thoughts that arose for 30 s (thought) and monitoring words that appeared onscreen for 30 s (word) while attending to the rising and falling of the abdomen (i.e., breathing). Subjects 16  reported with a first button press (index finger) to indicate when a thought arose or when a word appeared onscreen (see Stimuli), and with a second button press to indicate what type of thought or word it was (index = image or symbol, middle = narrative or inner speech, ring = emotion, pinky = body sensation) (Figure 2.1; see Appendix B for the complete task instructions). Each word stayed onscreen until the first button press. The first button press was followed by one gray asterisk (*) onscreen for 250 ms and the second button press was followed by two asterisks (**) onscreen for 250 ms to signal successful button presses. Each subject completed three 9-minute task runs, each consisting of 8 thought blocks and 8 word blocks separated by interstimulus intervals (ISIs) with jittered durations (randomly chosen from 250 ms, 500 ms, or 750 ms). The first button press corresponded to the act of noticing thoughts that arose during mindfulness meditation, whereas the second button press corresponded to the act of labeling the thoughts according to the categories routinely identified during mindfulness meditation (Sayadaw, 1985, 2002). In the thought condition, subjects were instructed to report mental events that took attention away from or became more prominent in attention than the breath. On the other hand, in the word condition, subjects were instructed to briefly think about the definition of the words presented before responding in order to elicit deliberate thought, instead of simply reacting to the appearance of the words onscreen. The onsets and categories of words presented within a word block were programmed to match the onsets and categories of self-caught thoughts reported in the previous thought block. Thus, each pair of thought and word blocks had the same frequencies and categories of events at approximately the same time points within each block (Figure 2.1). A period of 4 s (2 TRs) prior to the first button press was used to model the event onsets because a period of 2 s (1 TR) before the button press cut off the initial peak of MTL activation. In addition, a period of 6 s (3 TRs) prior to the button press yielded similar results as 17  a period of 4 s before the button press but excluded more trials (i.e., those that did not occur 6 s or more after a previous one). The comparison of thought and word events, specified 4 s before the corresponding first button press, enabled the examination of neural recruitment during spontaneous thought generation versus deliberate word processing. 18   Figure 2.1. Schematic of Experiment 1 task. For each task run, the subjects completed 8 cycles of monitoring thoughts for 30 s (thought) and monitoring words that appeared onscreen for 30 s (word). Subjects reported with a first button press (index finger) to indicate when a thought or word occurred, and with a second button press to indicate what type of thought or word it was (index = image or symbol, middle = narrative or inner speech, ring = emotion, pinky = body sensation). Event onsets were modeled 4 s before the first button press. The onsets and categories of words presented within a word block were programmed to match the onsets and categories of self-caught thoughts reported in the previous thought block. Thus, each pair of thought and word blocks had the same frequencies and categories of events at approximately the same time points within each block.  19  Stimuli  The words presented during word monitoring blocks were randomly chosen from four lists that corresponded to the categories of thoughts routinely identified during mindfulness meditation: image or symbol, narrative or inner speech, emotion, or body sensation (Sayadaw, 1985, 2002). Words in the image list consisted of 30 nouns (e.g., mountain, beach, rain, sun, pet) selected from the Medical Research Council (MRC) Psycholinguistics Database (Wilson, 1988), which had imageability, concreteness, and familiarity ratings of 500–700 (on scales of 100 = very low to 700 = very high) to ensure ease of visualization. Words in the narrative list consisted of 30 nouns (e.g., work, money, family, goals, health) selected from the Edinburgh Associative Thesaurus (EAT) (Kiss, Armstrong, Milroy, & Piper, 1973), which were associated with the types of current concerns that people tend to have and that are thought to be major determinants of spontaneous thought content (Klinger, 2009; Klinger & Cox, 1987). These included home and household matters; employment and finance; partner, family, and relatives; friends and acquaintances; love, intimacy, and sexual matters; self-changes; education and training; health and medical matters; spiritual matters; and hobbies, pastimes, and recreation (Klinger & Cox, 2004). Words in the emotion list consisted of 30 adjectives (e.g., calm, happy, sad, afraid, worried) also selected from the EAT that were associated with various emotions (e.g., happiness, sadness, anger, disgust, fear, surprise). Words in the body sensation list consisted of 30 nouns and adjectives similarly selected from the EAT that were associated with various body sensations (e.g., warmth, tickle, vibration, pressure, pain). Each word contained 3–10 letters and 1–3 syllables. The words and fixation cross appeared as gray text on a black background. The task and stimuli were implemented and presented using E-Prime 2.0 (Psychology Software Tools, Sharpsburg, PA). 20  fMRI data acquisition  Functional and structural MRI data were collected using a 3.0 Tesla Philips Intera MRI scanner (Best, Netherlands) with a standard head coil. Head movement was restricted using foam padding around the head. T2*-weighted functional images were acquired parallel to the anterior commissure/posterior commissure (AC/PC) line using a single-shot gradient echo-planar sequence (EPI; repetition time [TR] = 2 s, echo time [TE] = 30 ms, flip angle [FA] = 90°, field of view [FOV] = 240 × 240 × 143 mm, matrix size = 80 × 80, SENSE factor = 1.0). A total of 265 functional volumes were acquired for each task run, each including 36 interleaved axial slices (3 mm thick with 1 mm skip) covering the entire brain. Before functional imaging, an inversion recovery prepared T1-weighted structural volume was acquired in the same slice locations and orientation as the functional images using a fast spin-echo sequence (TR = 2 s, TE = 10 ms, FA = 90°, FOV = 224 × 224 × 143 mm, acquisition matrix size = 240 × 235, reconstructed matrix size = 480 × 480, inversion delay [IR] = 800 ms, spin-echo turbo factor = 5). fMRI data analysis fMRI data for each subject were preprocessed and analyzed using SPM8 (Statistical Parametric Mapping, Wellcome Department of Imaging Neuroscience, London, UK). Slice timing correction was performed using sinc interpolation and resampling with the middle (18th) slice as a reference point. All functional volumes were realigned to the first volume to correct for between-scan motion. The structural volume was coregistered to the mean functional image and segmented to extract a gray matter image. The segmented structural volume was then spatially normalized to a gray matter image of the Montreal Neurological Institute (MNI) template and resliced to a voxel size of 2 × 2 × 2 mm. The derived spatial transformations were applied to the 21  realigned functional volumes to bring them into standardized MNI space. Finally, the functional volumes were smoothed with an 8-mm full-width at half-maximum (FWHM) isotropic Gaussian kernel to compensate for residual between-subject variability after spatial normalization and to permit application of Gaussian random field theory for corrected statistical inference (Friston, Jezzard, & Turner, 1994). To ensure that statistical analysis was performed for all brain regions, including those where the signal might have been low due to susceptibility artifacts, a mask was created by averaging and thresholding the first preprocessed functional volume from all subjects and was explicitly specified during model estimation at the individual level. To remove low-frequency drift in the blood oxygen-level dependent (BOLD) signal, the data were high-pass filtered using an upper cut-off period of 128 s. No global scaling was performed.  Condition effects at each voxel were estimated according to the general linear model for the whole-brain analyses. The model included (a) the observed time series of intensity values, which represented the dependent variable; (b) covariates modeling session-specific effects (i.e., the six head movement parameters), later treated as confounds; and (c) regressor functions constructed by convolving condition-specific stick functions with a synthetic hemodynamic response function. The regressor functions were constructed to model each of the thought (timage, tnarrative, temotion, and tsensation), word (wimage, wnarrative, wemotion, and wsensation), and button press events and were compared using pairwise contrasts for each subject. Onsets for the thought and word events were specified at 4 s before the corresponding first button press. Group random-effects analyses were then performed for each contrast. The resulting T maps were subsequently transformed to the unit normal Z distribution to create a statistical parametric map for each contrast. The threshold for significance was set at p < 0.05 family-wise error [FWE] cluster corrected for multiple comparisons and extent threshold k > 20 voxels. 22  Time course extraction Percent signal change time courses for brain regions showing greater activation during thought events compared to word events were extracted for each subject using the MarsBaR toolbox in SPM8 (MARSeille Boîte À Région d’Intérêt; Brett, Anton, Valabregue, & Poline, 2002). The extraction volumes were 4-mm radius spheres centered on local maxima from the group-level contrasts, including ROIs in the default network (MPFC, PCC, and TPJ), MTL memory structures (HPC and PHC), TPC, RLPFC, and executive network (DLPFC and DACC). Eight finite impulse response (FIR) functions were used, one for each peristimulus time point within a trial window of 16 s following the onset of a thought or word event (specified at 4 s before the first button press). Network analysis Neural network recruitment during thought and word events was analyzed using Spatiotemporal Partial Least Squares (ST-PLS), which is a multivariate technique that identifies whole-brain patterns of neural activity correlated with different tasks or conditions over a period of time (McIntosh, Chau, & Protzner, 2004). In contrast to bivariate correlations – a common form of neural network analysis that identifies brain networks based on how activity in an ROI or seed region correlates with activity in other brain regions – ST-PLS examines network-related patterns of activity for the whole brain at once without predetermined seed regions (McIntosh et al., 2004). Furthermore, in contrast to independent components analysis (ICA) – another common form of neural network analysis that identifies brain networks by extracting components that explain most of the variance in the data irrespective of the experimental design – ST-PLS specifically identifies task-related components or network activity (McIntosh et al., 23  2004). Moreover, ST-PLS allows the examination of changes over time in these brain networks. Using the non-rotated version of task ST-PLS, which allows the specification of a priori non-orthogonal contrasts, one contrast was entered to examine differences in neural network recruitment between thought and word events (thought > word) within a trial window of 16 s following the onset of a thought or word trial (modeled at 4 s before the first button press). The statistical significance of the results at p < .05 was computed using permutation testing with 500 permutations. Correction for multiple comparisons was not necessary as the whole spatiotemporal pattern was tested in one analytical step instead of in a series of voxel-wise statistical tests. The reliability of the results was computed using bootstrap estimation of standard errors with 300 iterations. Reliable voxels were signified by bootstrap ratios of greater than +/- 2.576, which is approximately equal to a Z-score with p < .01.  Results Behavioral results  Subjects reported an average of 67.33 thoughts (SD = 35.02) throughout all scanning sessions, and an average of 2.81 thoughts (SD = 1.21) per thought block. However, only an average of 44.67 thoughts (SD = 15.03), or 73.80% of the thoughts reported, occurred 4 s or more after the previous thought report and were thus included in the analyses. Of the thoughts included, 18.66% (M = 8.33, SD = 10.28) were images, 37.31% (M = 16.67, SD = 5.55) were narrative, 12.94% (M = 5.78, SD = 5.86) were emotions, and 31.09% (M = 13.89, SD = 8.80) were body sensations. A one-way repeated measures ANOVA at the α = .05 level indicated that the number of thought reports differed significantly across the four thought types [F(3,51) = 7.01, p < .001]. Follow-up multiple paired t-tests with a Bonferroni correction (α = .05 / 6 = 24  .0083) revealed that there were significantly more narrative reports [t(17) = 6.82, p < .001] and body sensation reports [t(17) = 4.39, p < .001] than emotion reports. Thus, it appears that narrative thoughts were the most often reported type of event, followed by body sensations, images, and emotions. SPM results To identify the brain regions that demonstrated relatively increased recruitment during spontaneous thought, thought events were compared to word events (thought > word). There was greater activation during thought trials than during word trials (Figure 2.2a, Table 2.1) in default network regions, including the MPFC (Brodmann area [BA] 10; peak x, y, z = 2, 52, 12), PCC (BA 31; peak x, y, z = -14, -46, 30), and right TPJ (BA 39; peak x, y, z = 44, -76, 36). Greater activation during thought trials was also observed in MTL memory structures, including the left HPC (peak x, y, z = -26, -20, -22), right HPC (peak x, y, z = 24, -14, -18), left PHC (BA 36; peak x, y, z = -16, -22, -22), and right PHC (BA 36; peak x, y, z = 16, -36, -16). Thought trials were also associated with greater activation in the left TPC (BA 38; peak x, y, z = -44, -2, -44), right TPC (BA 38; peak x, y, z = 32, 6, -32), left RLPFC (BA 10; peak x, y, z = -30, 56, 14), and right RLPFC (BA 10; peak x, y, z = 18, 58, 22). Increases in activation during thought events were also observed in executive network regions, including the left DLPFC (BA 9; peak x, y, z = -28, 44, 28) and DACC (BA 32; peak x, y, z = 0, 26, 26). Other increases in activation were observed in the bilateral mid-insula, bilateral postcentral gyrus, bilateral superior temporal gyrus (STG), supplementary motor area (SMA), bilateral superior parietal lobule (SPL), and left posterior cerebellum. To identify the brain regions that showed relatively increased recruitment during 25  deliberate word processing, word events were compared to thought events (word > thought). There was greater activation during word trials than during thought trials (Figure 2.2b, Table 2.2) in the left ventral LPFC (VLPC), including the left pars opercularis (BA 44; peak x, y, z = -44, 12, 18), left pars triangularis (BA 45; peak x, y, z = -52, 36, 10), and left pars orbitalis (BA 47; peak x, y, z = -50, 26, -4). Together, the left pars opercularis and pars triangularis roughly correspond to Broca’s area. Word trials were also associated with greater activation in the visual cortex, including the left superior occipital gyrus (SOG; BA 18; x, y, z = -26, -86, 6), left middle occipital gyrus (MOG; BA 18; peak x, y, z = -14, -94, -2), and left inferior occipital gyrus (IOG; BA 18; peak x, y, z = -28, -84, -12). Other increases in activation were observed in the bilateral fusiform gyrus, left intraparietal sulcus (IPS), and left premotor area (PMA). Entering the subjects’ number of reported thoughts, hours of meditation experience, and age in years as covariates in the analysis did not alter the significance of the results, and yielded similar activation maps for both the thought > word and word > thought contrasts. Thus, thought events were associated with preferential recruitment of the brain regions consistently implicated in previous studies of spontaneous thought, whereas word events were associated preferential recruitment of brain areas that support language and visual processing. 26   Figure 2.2. Activation maps for thought and word events. (a) Thought trials (thought > word) were associated with activation in the default network (MPFC, PCC, and TPJ), MTL memory structures (HPC and PHC), TPC, RLPFC, and the executive network (DLPFC and DACC). Activations were also observed in the mid-insula (INS), postcentral gyrus, STG, SMA, SPL, and posterior cerebellum. (b) Word trials (word > thought) were associated with activation in the left VLPFC (pars opercularis, pars triangularis, and pars orbitalis) and the visual (VIS) cortex (IOG, MOG, and SOG). Activations were also observed in the fusiform gyrus, IPS, and PMA. Thought events were thus associated with recruitment of brain regions consistently implicated in studies of spontaneous thought, whereas word events were associated with recruitment of brain areas that support language and visual processing. Results are displayed in neurological orientation on the experiment-specific average brain. All activations were significant at p < .05 FWE cluster corrected and k > 20. 27  Table 2.1. Activation peaks for thought events (thought > word).   MNI coordinates  Region L/R/M BA x y z Voxels Z value Frontal        Ventral ACC M 24 0 36 14 659 5.02 Dorsal ACC M 32 0 26 26 178 4.25 Superior frontal gyrus (MPFC) M 10 2 52 12 33 3.71 Middle frontal gyrus (RLPFC) L 10 -30 56 14 81 3.90 Middle frontal gyrus (RLPFC) R 10 18 58 22 357 3.46 Middle frontal gyrus (DLPFC) L 9 -28 44 28 251 4.51 Mid-insula L 13 -36 6 -12 55 3.28 Mid-insula R 13 46 4 -2 505 4.86 Posterior insula R 13 36 -20 16 32 3.50 Supplementary motor area M 6 0 -26 66 165 3.14 Parietal        Posterior cingulate cortex M 31 -14 -46 30 55 3.15 Angular gyrus R 39 44 -76 36 30 4.08 Superior parietal lobule L 5 -22 -38 58 31 2.86 Superior parietal lobule R 5 20 -42 56 117 2.88 Postcentral gyrus L 43 -50 -4 4 81 3.81 Postcentral gyrus R 43 52 -10 14 33 4.21         28    MNI coordinates  Region L/R/M BA x y z Voxels Z value Temporal        Hippocampus L 28 -26 -20 -22 33 4.74 Hippocampus R 28 24 -14 -18 81 4.03 Parahippocampus L 36 -16 -22 -22 33 3.75 Parahippocampus R 36 16 -36 -16 184 4.13 Temporopolar cortex L 38 -44 -2 -44 122 3.52 Temporopolar cortex R 38 32 6 -32 61 3.52 Superior temporal gyrus L 22 -54 -10 6 33 3.55 Superior temporal gyrus R 22 60 -2 0 113 5.06 Subcortical        Dentate of cerebellum M - -14 -48 -34 47 3.34 Posterior cerebellum L - -48 -62 -36 232 3.92 Note. All activations were significant at p < .05 FWE cluster corrected and k > 20. 29  Table 2.2. Activation peaks for word events (word > thought).   MNI coordinates   Region L/R/M BA x y z Voxels Z value Frontal        Inferior frontal gyrus             (pars opercularis)  L 44 -44 12 18 32 3.66 Inferior frontal gyrus             (pars triangularis)  L 45 -52 36 10 30 3.21 Inferior frontal gyrus             (pars orbitalis)  L 47 -50 26 -4 162 2.87 Premotor area L 6 -44 4 28 708 4.35 Parietal        Intraparietal sulcus L 19 -26 -72 32 481 5.42 Occipital        Superior occipital gyrus L 18 -26 -86 6 33 5.18 Middle occipital gyrus L 18 -14 -94 -2 380 5.43 Middle occipital gyrus R 18 28 -82 -6 327 6.31 Inferior occipital gyrus L 18 -28 -84 -12 33 5.02 Temporal        Fusiform gyrus L 37 -34 -50 -16 81 6.06 Fusiform gyrus R 37 32 -62 -14 257 5.38 Note. All activations were significant at p < .05 FWE cluster corrected and k > 20. 30  Time course results To more closely examine how the brain areas that showed greater activation during thought events relative to word events contributed to the results, percent signal change time courses for ROIs in the MPFC, PCC, right TPJ, left HPC, left PHC, right TPC, left RLPFC, left DLPFC, and DACC were extracted and plotted (Figure 2.3). Activation in the HPC, PHC, PCC, and TPJ peaked before the button press, 2 s after the onset of thought events. In addition, activation in the MPFC and TPC peaked during the button press, 4 s after the onset of thought events. Finally, activation in the RLPFC, DLPFC, and DACC peaked after the button press, 6 s after the onset of thought events. The early recruitment of MTL memory structures (HPC and PHC) and the posterior components of the default network (PCC and TPJ) suggests that they may contribute to the initial generation of spontaneous thought. In contrast, the late recruitment of the anterior component of the default network (MPFC), TPC, RLPFC, and executive network (DLFPC and DACC) suggests that they may instead contribute to the subsequent elaboration and evaluation of spontaneous thought. 31   Figure 2.3. Time courses during thought and word events. The line graphs represent mean percent signal change over time for each condition in 4-mm radius spheres centered on local maxima from the group-level thought > word contrast. Event onsets were 4 s before the first button press, which is marked by the gray vertical lines. Error bars represent the standard error of the mean. During thought events, HPC, PHC, PCC, and TPJ activation peaked before the button press at 2 s after event onset, whereas MPFC and TPC activation peaked during the button press at 4 s, and RLPFC, DLPFC, and DACC activation peaked after the button press at 6 s. Thus, MTL memory structures (HPC and PHC) and posterior default network components (PCC and 32  TPJ) may contribute more to the initial generation of spontaneous thought, whereas anterior default network (MPFC), TPC, RLPFC, and executive network areas (DLPFC and DACC) may contribute more to the subsequent elaboration and evaluation of spontaneous thought.  ST-PLS results To identify neural networks that demonstrated relatively increased recruitment during spontaneous thought, thought events were compared to word events (thought > word) using ST-PLS. The contrast of thought trials relative to word trials was significant with p < .001. Relative to thought events, word events – indicated by negative saliences, or how much a voxel’s increases and decreases in activity were associated with the negatively weighted or word condition (shown in cool colors in Figure 2.4, Table 2.4) – showed greater correlated activity between language and visual processing regions that also showed greater activation during word events compared to thought events. These regions included the left VLPFC (pars opercularis and pars triangularis), bilateral visual cortex (IOG, MOG, and SOG), bilateral fusiform gyrus, bilateral IPS, and bilateral PMA. Relative to word events, thought events – indicated by positive saliences, or how much a voxel’s increases and decreases in activity were associated with the positively weighted or thought condition (shown in warm colors in Figure 2.4, Table 2.3) – showed greater correlated activity between regions that also showed greater activation during thought events. The left HPC, left PHC, and bilateral TPJ showed greater correlated activity before the first button press at 2 s after event onset. These regions then showed increased correlated activity with the MPFC, PCC, bilateral mid-insula, bilateral TPC, bilateral DLPFC, and DACC during the button press at 4 s 33  after event onset. The bilateral DLPFC and DACC afterwards showed greater correlated activity with the bilateral RLPFC after the button press at 6 s after event onset. Thus, it appears that a subcomponent of a larger network consisting of MTL memory structures (HPC and PHC) and a posterior region of the default network (TPJ) was engaged during the initial generation of spontaneous thoughts. In addition, a second subcomponent including midline regions of the default network (MPF and PCC) and TPC was engaged during the subsequent elaboration of spontaneous thoughts. Finally, a third subcomponent including the RLPFC and executive network regions (DLPFC and DACC) was recruited during further metacognitive monitoring and evaluation of spontaneous thoughts. 34   Figure 2.4. Whole-brain network maps for thought and word events. During word events (cool colors), language and visual processing brain regions showed correlated activity, including the left VLPFC, visual cortex (IOG, MOG, and SOG), fusiform gyrus, IPS, and PMA. During thought events (warm colors), the MTL (left HPC and left PHC) and TPJ showed correlated activity before the first button press (TR 2) and then showed correlated activity with the MPFC, PCC, mid-insula, TPC, DLPFC, and DACC during the button press (TR 3). The DLPFC and DACC then showed correlated activity with the RLPFC after the button press (TR 4). Thus, a subcomponent of a larger network consisting of MTL memory structures (HPC and PHC) and a posterior region of the default network (TPJ) may support the initial generation of spontaneous thoughts. In addition, a subcomponent including midline regions of the default network (MPF and PCC) and TPC may support the subsequent elaboration of spontaneous thoughts. Finally, another subcomponent including the RLPFC and executive network regions (DLPFC and DACC) may contribute to further metacognitive monitoring and evaluation of spontaneous thoughts. Results are displayed in neurological orientation on the experiment-specific average brain and were thresholded using a bootstrap ratio of +/- 2.576 (equivalent to p < .01). Clusters had a spatial extent of at least 50 voxels. 35  Table 2.3. Whole-brain network clusters for thought events (thought > word).   MNI coordinates   Region L/R/M BA x y z BSR TRs active Frontal        Medial orbital gyrus (VMPFC) M 11 -8 38 -14 9.52 3*, 4 Superior frontal gyrus (RMPFC) M 10 2 48 6 6.86 2, 3, 4* Dorsal ACC M 24 -2 18 24 4.11 3, 4* Mid-cingulate gyrus (MCC) M 24 -10 -16 44 4.88 4* Middle frontal gyrus (DLPFC) L 9 -22 40 44 6.68 2, 3*, 4 Middle frontal gyrus (DLPFC) R 9 28 38 30 4.79 2, 3, 4* Middle frontal gyrus (RLPFC) L 10 -22 58 24 3.69 3, 4* Middle frontal gyrus (RLPFC) R 10 24 54 24 3.23 3, 4* Lateral orbital gyrus (VLPFC) R 47 52 34 -12 3.76 3* Mid-insula R 13 38 4 -10 4.27 3*, 4 Posterior insula L 13 -40 -26 6 3.74 3, 4* Posterior insula R 13 48 -10 4 5.26 3*, 4 Supplementary motor area M 6 4 32 62 3.68 2, 3* Parietal        Posterior cingulate cortex M 31 0 -60 26 5.58 2, 3*,4 Angular gyrus L 39 -46 -74 32 6.63 2, 3*, 4 Angular gyrus R 39 50 -74 26 5.46 2, 3*, 4 Supramarginal gyrus R 40 50 -62 46 7.58 2*, 3, 4         36    MNI coordinates   Region L/R/M BA x y z BSR TRs active Temporal        Hippocampus L - -14 -36 0 5.51 2*, 3 Hippocampus R - 32 -24 -14 3.78 2, 3*, 4 Parahippocampus L 36 -20 -20 -22 3.23 2*, 3 Parahippocampus R 36 14 -38 -6 4.57 2*, 3 Temporopolar cortex R 38 46 2 -38 4.54 3*, 4 Superior temporal gyrus L 22 -64 0 8 4.57 3* Superior temporal gyrus R 22 62 -6 8 5.08 3, 4* Middle temporal gyrus R 21 68 -8 -12 4.60 2*, 3, 4 Occipital        Cuneus M 19 4 -92 28 6.27 2*, 3 Subcortical        Mediodorsal thalamus M - -4 -12 -2 3.32 4* Anterior cerebellum R - 28 -32 -30 4.74 2*, 3 Posterior cerebellum L - -46 -64 -38 4.02 2, 3* Posterior cerebellum R - 46 -66 -36 5.01 2*, 3  Note. For each cluster, the TRs of activation are noted, and the peak of activation (from which the bootstrap ratio and coordinates were taken) is indicated by an asterisk. All clusters had bootstrap ratios (BSR) greater than +/- 2.576 (equivalent to p < .01) and had a spatial extent of at least 50 voxels.  37  Table 2.4. Whole-brain network clusters for word events (word > thought).   MNI coordinates   Region L/R/M BA x y z BSR TRs active Frontal        Inferior frontal gyrus            (pars triangularis) L 45 -38 24 20 -9.33 2*, 3, 4 Inferior frontal gyrus            (pars triangularis) R 45 50 30 8 -4.74 4* Inferior frontal gyrus            (pars opercularis) L 44 -38 12 24 -10.75 2, 3*, 4 Inferior frontal gyrus            (pars opercularis) R 44 34 6 26 -7.15 2*, 3, 4 Anterior insula L 13 -28 22 6 -4.51 2, 3* Premotor area R 6 26 -2 58 -5.75 2, 3* Premotor area L 6 -48 8 42 -4.82 2, 3*, 4 Parietal        Superior parietal lobule L 7 -40 -54 56 -5.93 2, 3, 4* Postcentral gyrus (S1) L 3 -42 -24 54 -10.51 2*, 3 Postcentral gyrus (S1) R 2 36 -40 44 -6.11 2*, 3 Postcentral gyrus (S2) L 43 -52 -22 18 -6.80 2*, 3 Occipital        Middle occipital gyrus L 18 -12 -90 4 -7.81 2, 3*, 4 Middle occipital gyrus R 18 22 -92 4 -8.28 2*, 3, 4 Lingual gyrus L 17 -10 -86 0 -10.69 2, 3, 4* 38    MNI coordinates   Region L/R/M BA x y z BSR TRs active Lingual gyrus R 17 14 -74 8 -11.28 3*, 4 Temporal        Superior temporal gyrus L 22/39 -54 -50 16 -6.79 2*, 3, 4 Superior temporal gyrus R 22/39 48 -40 10 -5.37 2, 3*, 4 Subcortical        Ventral lateral thalamus L - -10 -18 8 -7.46 2, 3* Superior colliculus M - -2 -30 -6 -6.63 2*, 3 Note. For each cluster, the TRs of activation are noted, and the peak of activation (from which the bootstrap ratio and coordinates were taken) is indicated by an asterisk. All clusters had bootstrap ratios (BSR) greater than +/- 2.576 (equivalent to p < .01) and had a spatial extent of at least 50 voxels.  39  Discussion Experiment 1 examined the temporal dynamics of brain activity during spontaneous thought and which of the brain regions consistently implicated in spontaneous thought contribute specifically to its initial generation. To do so, the study compared subject- or self-caught spontaneous thought events with prompted, deliberate thought events (i.e., processing words of the same type as the thoughts reported). Spontaneous thought events were associated with preferential recruitment of default network areas (MPFC, PCC, and TPJ), MTL memory structures (HPC and PHC), TPC, RLPFC, and executive network areas (DLPFC and DACC). However, extracted time courses showed that the MTL, PCC, and TPJ displayed increased activation before the other brain regions, whereas whole-brain network analysis showed that activity in the MTL and TPJ correlated with activity in the other regions only after initial MTL and TPJ recruitment. The earlier recruitment of a subgroup of brain areas that support spontaneous thought, including MTL memory structures (HPC and PHC) and the posterior regions of the default network (PCC and TPJ), suggests that these areas may contribute specifically to the initial generation of spontaneous thought. In addition, time courses of brain activation and temporal patterns of neural network recruitment revealed that the MPFC and TPC were recruited after the MTL, PCC, and TPJ, followed by executive network regions (LPFC and DACC), suggesting the engagement of different levels of processing during the flow of spontaneous thought. Neural correlates of spontaneous thought The recruitment of default network areas (MPFC, PCC, and TPJ), MTL memory structures (HPC and PHC), TPC, RLPFC, and executive network areas (DLPFC and DACC) 40  during spontaneous thought in Experiment 1 replicated the pattern of brain activation frequently associated with spontaneous thought in previous studies with non-meditator subjects (Christoff, 2012). In addition, specifying hours of meditation experience as a covariate of no interest in Experiment 1 showed recruitment of the same brain networks and regions during spontaneous thought as the original analyses, suggesting that the results were independent of meditation experience. Thus, the pattern of brain activation identified during spontaneous thought in Experiment 1 may not necessarily be specific to experienced meditators and may instead reflect more general neural processes supporting spontaneous thought. However, in contrast with previous studies of spontaneous thought, the comparison of thought events reported during scanning and word events that matched the type of thoughts reported in Experiment 1 enabled a more stringent assessment of neural recruitment during spontaneous thought. Thus, compared to results from previous studies, the pattern of brain activation identified in Experiment 1 also more directly reflected neural recruitment specific to spontaneous thought processes. Order of neural recruitment during spontaneous thought  The sequence of neural recruitment during spontaneous thought revealed by the extracted time courses and whole-brain network analysis in Experiment 1 is consistent with previously proposed roles for the MTL, PCC, and TPJ in spontaneous thought (Andrews-Hanna, Smallwood, & Spreng, 2014; Buckner et al., 2008). During the generation of spontaneous thought, the MTL may construct mental simulations of past, future, and novel events (Addis et al., 2007; Botzung et al., 2008; Hassabis et al., 2007; Okuda et al., 2003; Szpunar et al., 2009), with the PHC forming or accessing old semantic and episodic associations (Aminoff, Gronau, & Bar, 2007; Bar et al., 2008) and the HPC recombining these associations with other information 41  (Schacter & Addis, 2009). The TPJ may direct attention and integrate inputs from multiple sensory and limbic areas (Decety & Lamm, 2007) based on the outputs of MTL processes, such as spontaneously retrieved memories (Cabeza, Ciaramelli, Olson, & Moscovitch, 2008). The PCC may serve as the interface between the PFC (e.g., MPFC and LPFC) and the MTL and TPJ, representing relevant, internally generated information based on the integration of inputs from the association cortices (e.g., TPJ) and memory regions (e.g., MTL). This information is then subjected to inferential and evaluative processes (e.g., by the MPFC and LPFC) to guide behavior (Buckner et al., 2008; Leech et al., 2012; Vogt & Laureys, 2005).  The pattern of brain activation identified in Experiment 1 is also consistent with previously proposed roles for the MPFC, RLPFC, DLPFC, and DACC in spontaneous thought (Andrews-Hanna et al., 2014; Buckner et al., 2008). During the elaboration of spontaneous thought, the MPFC may facilitate the initial evaluation and thus the continuation of spontaneous thought events by performing inductive inferences on self-generated mental content from the MTL, TPJ, and PCC (Buckner et al., 2008; Gusnard, Akbudak, Shulman, & Raichle, 2001; Vogt & Laureys, 2005). In addition, the MPFC, which is commonly activated during self-processing, may relate arising thoughts to one’s self-concept and evaluate these thoughts for their relevance to one’s goals (Denny, Kober, Wager, & Ochsner, 2012).  During further evaluation of spontaneous thought events, as part of the executive network, the DACC may support salience or conflict detection processes that signal the need for increased cognitive control and thus facilitate attention focusing and shifting (Carter et al., 1999; Carter et al., 1998), such as during the monitoring of spontaneous thought occurrence. The DLPFC then integrates and evaluates the relevance (defined in terms of current task rules and goals) of inputs from the DACC, other prefrontal areas, memory regions, and association cortices 42  in order to implement the cognitive control required (Carter & van Veen, 2007; Fleck et al., 2006; MacDonald et al., 2000). In turn, the RLPFC integrates and evaluates the outputs of prior stages of cognitive processing, especially at high levels of abstraction, such as those coming from the MPFC and DLPFC (Christoff & Gabrieli, 2000; Christoff et al., 2009c; Christoff, Ream, Geddes, & Gabrieli, 2003; Fletcher & Henson, 2001; Petrides, 2005; Ramnani & Owen, 2004; Smith, Keramatian, & Christoff, 2007; Tsujimoto, Genovesio, & Wise, 2010). Thus, information about the occurrence and progression of spontaneous thoughts collected in the present experiment helped to provide empirical support for the theorized sequence of neural processes during spontaneous thought. Generative subsystem of a spontaneous thought network  The early recruitment of the MTL, PCC, and TPJ in Experiment 1 that suggests they may be central to the initial generation of spontaneous thought expands upon a number of previous studies that have linked these regions to the spontaneous generation of mental content, such as visual imagery and conceptual representations, drawn from past experience. For example, the MTL has been associated with the spontaneous reactivation of memories (Gelbard-Sagiv et al., 2008) and the spontaneous reactivation of both task-relevant and task-irrelevant information during memory retrieval (Kuhl, Johnson, & Chun, 2013). The MTL and PCC have also been associated with the spontaneous replay of recent experiences during rest and sleep (Rasch & Born, 2007), especially in rats (Foster & Wilson, 2006; Karlsson & Frank, 2009; Sutherland & McNaughton, 2000). In addition, the inferior parietal lobule (IPL), which includes the TPJ, has been associated with the spontaneous retrieval of contextual details for autobiographical memories, which is impaired in patients with IPL lesions (Berryhill et al., 2007). The IPL has 43  also been proposed to support the spontaneous or bottom-up capture of attention by episodic memories (Cabeza et al., 2008). Thus, the identification of the brain regions engaged during the initial generation of spontaneous thought through the collection of information about the onset of spontaneous thoughts in the present experiment helped to provide more direct support for the generative role of the MTL, PCC, and TPJ during spontaneous thought flow. Elaborative subsystem of a spontaneous thought network The pattern of neural recruitment revealed in Experiment 1 suggests that the anterior component of the default network (MPFC), TPC, RLPFC, and executive network areas (DLPFC and DACC) may contribute to the elaboration of spontaneous thought. The extracted time courses showed that the MPFC, TPC, RLPFC, DLPFC, and DACC displayed increased activation after MTL, PCC, and TPJ recruitment. In addition, whole-brain network analysis showed that activity in the MPFC, TPC, RLPFC, DLPFC, and DACC, as well as the PCC, correlated with activity in the MTL and TPJ after initial MTL and TPJ recruitment. However, although the examination of spontaneous thought onset in Experiment 1 allowed the results to capture neural recruitment during the generation of spontaneous thought, it provided only indirect evidence for the brain regions that support the elaboration of spontaneous thought. In addition, Experiment 1 did not distinguish between initial, spontaneous, affective elaboration processes and subsequent, deliberate, metacognitive evaluation processes during spontaneous thought flow. Furthermore, although the time course for the PCC during spontaneous thought showed earlier activation along with the MTL and TPJ before other brain regions, whole-brain network analysis showed that activity in the PCC did not correlate with initial MTL and TPJ activity but correlated with later activity in the MPFC and LPFC. Hence, it is not clear whether 44  PCC recruitment is specific to spontaneous thought generation or supports spontaneous thought elaboration instead. Thus, a second experiment was conducted to more directly examine neural recruitment when thoughts are followed by or linked to other thoughts during the elaboration of spontaneous thought. 45  CHAPTER 3 – EXPERIMENT 2: SPONTANEOUS THOUGHT ELABORATION Late recruitment of the anterior component of the default network (MPFC), TPC, RLPFC, and executive network regions (DLPFC and DACC) during spontaneous thought events in Experiment 1 suggests that they support the elaboration, instead of the generation, of spontaneous thought. However, this provides only indirect evidence for the contributions of these brain areas to spontaneous thought elaboration. In addition, Experiment 1 did not distinguish between initial, spontaneous, affective elaboration processes and subsequent, deliberate, metacognitive evaluation processes during spontaneous thought flow. Thus, Experiment 2 aimed to more directly assess neural recruitment when thoughts are followed by or linked to other thoughts during the elaboration of spontaneous thought.  In this experiment, subjects were instructed to press a button to indicate the occurrence or absence of a second spontaneous thought after an initial spontaneous thought. This approach enabled the examination of neural recruitment specifically during spontaneous thought elaboration (i.e., when a second thought followed the initial thought) as well as during spontaneous thought dissolution (i.e., when no thought followed the initial thought). The anterior component of the default network (MPFC) appears to contribute to spontaneous, affective evaluations of inputs from memory regions, association cortices, and other prefrontal areas, which may result in the continuation of spontaneous thought flow. Thus, spontaneous thought elaboration was hypothesized to preferentially recruit the MPFC. In addition, it was predicted that spontaneous thought dissolution would be associated with no change in activation in the MTL and MPFC, which may reflect the return of generative and elaborative neural processes back to baseline levels of activation. 46  Methods Subjects Sixteen subjects (after 4 exclusions; 8 male and 8 female; M = 49.49 years old, SD = 11.77, range = 29.39 – 68.42) from Experiment 1 also participated in Experiment 2. The subjects were long-term, expert mindfulness meditators with more than 3,000 hours of lifetime meditation experience and at least 1 hour of daily practice in the Mahasi Vipassana tradition (M = 8,883.50 hours, SD = 6,146.74, range = 3,174 – 23,700). The same meditation experience questionnaire (Appendix A) and phone interview procedures as in Experiment 1 were administered to ensure consistency of the meditation technique across subjects and attainment of extensive knowledge of and experience with the meditation technique through regular practice and attendance of several long-term intensive retreats. The subjects were recruited from Vipassana meditation communities in Vancouver (BC, Canada), Vancouver Island (BC, Canada), Boulder (CO, USA), San Francisco (CA, USA), and Seattle (WA, USA). All subjects had normal or corrected-to-normal vision with no MRI contraindications or current psychiatric medication use. Twelve were right-handed and 4 were left-handed, but all used their right hand to respond during the experiment. Two subjects were excluded from the analyses due to excessive motion (1 with > 5° pitch rotation, and 1 with > 5° pitch rotation and > 5 mm in the z-direction). Two subjects were excluded from the analyses because they reported fewer than five instances of two consecutive thoughts (one and two instances, respectively). All protocols were approved by the UBC Clinical Research Ethics Board and the UBC MRI Research Center. All subjects gave informed written consent prior to participating and received payment as compensation. 47  Procedure   One to two days prior to the actual scanning session, subjects engaged in a practice session identical to the actual scanning procedure in a mock scanner environment to become acclimatized to the task, button pressing, and scanner noises. As in Experiment 1, subjects alternated between monitoring thoughts that arose for 30 s (thought) and monitoring words that appeared onscreen for 30 s (word) while attending to the rising and falling of the abdomen (i.e., breathing). However, in Experiment 2, subjects waited 1–2 s, or approximately the length of one inhalation-exhalation cycle, after a thought occurred to see if it was followed by a second thought (Figure 3.1; see Appendix B for the complete task instructions). They reported with an index finger button press if no thought followed the first thought (i.e., one thought occurred then “dissolved” and was followed by no other thought). They reported with a middle finger button press if a second thought followed the first thought (i.e., two thoughts occurred, where one thought occurred then “dissolved” and was followed by a second thought).  Subjects also reported with an index finger button press if no word appeared onscreen after a first word (i.e., one word appeared then disappeared and was followed by dashes, “---”). They also reported with a middle finger button press if a second word appeared after the first word (i.e., two words appeared, where one word appeared then disappeared and was followed by another word onscreen). The first word appeared onscreen for 500 ms, and the dashes or second word stayed onscreen until the button press. To signal successful responses, the button press was followed by one gray asterisk (*) onscreen for 250 ms if only one thought or word was reported and by two asterisks (**) for 250 ms if two consecutive thoughts or words were reported. Nine subjects completed two 9-minute task runs and seven subjects completed three 9-minute task runs. Each task run consisted of 8 thought blocks and 8 word blocks separated by ISIs with 48  jittered durations (randomly chosen from 250 ms, 500 ms, or 750 ms). As in Experiment 1, in the thought condition, subjects were instructed to report mental events that took attention away from or became more prominent in attention than the breath. In the word condition, subjects were instructed to briefly think about the definition of the words presented before responding in order to elicit deliberate thought, instead of simply reacting to the appearance of the words onscreen. The onsets and types (i.e., one/single or two/consecutive) of words presented within a word block were programmed to match the onsets and types of self-caught thoughts reported in the previous thought block. Thus, each pair of thought and word blocks had the same frequencies and types of events at approximately the same time points within each block (Figure 3.1). The comparison of thought elaboration (i.e., when a second thought followed an initial thought) and thought dissolution events (i.e., when no thought followed an initial thought), specified 4 s before the corresponding button press, enabled the examination of neural recruitment during the elaboration of spontaneous thought. 49   Figure 3.1. Schematic of Experiment 2 task. For each task run, the subjects completed 8 cycles of monitoring thoughts for 30 s (thought) and monitoring words that appeared onscreen for 30 s (word). Subjects reported with an index finger button press if no thought or word followed the initial one (i.e., one thought or one word occurred) and with a middle finger button press if a second thought or word followed the initial one (i.e., two thoughts or words occurred). Event onsets were modeled 4 s before the button presses. The onsets and types (i.e., one/single or two/consecutive) of words presented within a word block were programmed to match the onsets and types of self-caught thoughts reported in the previous thought block. Thus, each pair of thought and word blocks had the same frequencies and types of events at approximately the same time points within each block. 50  Stimuli  The words presented in Experiment 2 were randomly chosen from the same four lists used in Experiment 1, which included 30 image words, 30 narrative words, 30 emotion words, and 30 body sensation words. The lists corresponded to the categories of thoughts routinely identified during mindfulness meditation (Sayadaw, 1985, 2002), as well as common types of current concerns that tend to form spontaneous thought content (Klinger, 2009; Klinger & Cox, 1987, 2004).  fMRI data acquisition  Functional and structural MRI data for Experiment 2 were collected using the same scanning protocol as in Experiment 1. T2*-weighted functional images were acquired parallel to the AC/PC line using a single-shot gradient EPI sequence (TR = 2 s, TE = 30 ms, FA = 90°, FOV = 240 × 240 × 143 mm, matrix size = 80 × 80, SENSE factor = 1.0). A total of 265 functional volumes were acquired for each task run, each including 36 interleaved axial slices (3 mm thick with 1 mm skip) covering the entire brain. An inversion recovery prepared T1-weighted structural volume was also acquired in the same slice locations and orientation as the functional images using a fast spin-echo sequence (TR = 2 s, TE = 10 ms, FA = 90°, FOV = 224 × 224 × 143 mm, acquisition matrix size = 240 × 235, reconstructed matrix size = 480 × 480, IR = 800 ms, spin-echo turbo factor = 5). fMRI data analysis Data for Experiment 2 were preprocessed and analyzed using the same SPM8 procedures as in Experiment 1. In Experiment 2, the regressor functions were constructed to model each of the thought dissolution, thought elaboration, word dissolution, word elaboration, and button 51  press events and were compared using pairwise contrasts for each subject. Onsets for the thought and word events were specified at 4 s before the corresponding button press. Group random-effects analyses were then performed for each contrast. The resulting T maps were transformed to the unit normal Z distribution to create a statistical parametric map for each contrast. The threshold for significance was set at p < 0.05 FWE cluster corrected for multiple comparisons and extent threshold k > 20 voxels. Time course extraction Percent signal change time courses for Experiment 2 were extracted using the same MarsBaR procedures as in Experiment 1. In Experiment 2, the extraction volumes were 4-mm radius spheres centered on local maxima from the group-level contrasts (thought elaboration > thought dissolution and thought dissolution > thought elaboration), including ROIs in the MPFC (ventral / VACC and rostral / RMPFC) and MTL (HPC and PHC). Eight FIR functions were specified, one for each peristimulus time point within a trial window of 16 s following the onset of a thought or word event (computed at 4 s before the button press). Network analysis Neural network recruitment in Experiment 2 was analyzed using the same ST-PLS procedures as in Experiment 1. In Experiment 2, the contrast entered examined differences in neural network recruitment between spontaneous thought elaboration and spontaneous thought dissolution events (thought elaboration > thought dissolution). The statistical significance of the results at p < .05 was determined using permutation testing with 500 permutations. The reliability of the results was determined using bootstrap estimation of standard errors with 300 iterations. Reliable voxels were signified by bootstrap ratios of greater than +/- 1.96, which is 52  approximately equal to a Z-score with p < .05. Results Behavioral results  Subjects reported an average of 50.31 thoughts (SD = 29.83) throughout all scanning sessions, and an average of 2.58 thoughts (SD = 1.08) per thought block. However, only an average of 39.50 thoughts (SD = 20.24), or 82.25% of the thoughts reported, occurred 4 s or more after the previous thought report and were thus included in the analyses. Of the thoughts included, 61.23% (M = 24.19, SD = 11.64) were single thoughts and 38.77% (M = 15.31, SD = 12.25) were two consecutive thoughts. A paired t-test at the α = .05 level showed that there were significantly more reports of single thoughts (i.e., spontaneous thought dissolution) than reports of two consecutive thoughts (i.e., spontaneous thought elaboration) [t(15) =  2.79, p = .01]. SPM results To identify the brain regions that demonstrated relatively increased recruitment when there was no elaboration of spontaneous thought (i.e., when no thought followed an initial thought), spontaneous thought dissolution events were compared to spontaneous thought elaboration events (thought dissolution > thought elaboration). There was greater activation during spontaneous thought dissolution than during spontaneous thought elaboration (Figure 3.2b, Table 3.2) in the MTL, including the left HPC (peak x, y, z = -18, -24, -10), right HPC (peak x, y, z = 18, -22, -12), and left PHC (BA 36; peak x, y, z = -14, -34, -10). Other increases in activation during spontaneous thought dissolution were observed in the right mid-insula, mediodorsal thalamus, right putamen, right supramarginal gyrus, right middle temporal gyrus (MTG), right superior temporal gyrus (STG), and bilateral cerebellum. 53  To identify the brain regions that demonstrated relatively increased recruitment during the elaboration of spontaneous thought (i.e., when a second thought followed an initial thought), spontaneous thought elaboration events were compared to spontaneous thought dissolution events (thought elaboration > thought dissolution). There was greater activation during spontaneous thought elaboration than during spontaneous thought dissolution (Figure 3.2a, Table 3.1) in the MPFC, including the rostral / RMPFC (BA 10; peak x, y, z = 6, 66, 4), dorsal / DMPFC (BA 9; peak x, y, z = -8, 54, 22), ventral / VACC (BA 32; peak x, y, z = -12, 48, 0), and rostral / RACC (BA 32; peak x, y, z = 8, 52, 12). Entering the subjects’ number of reported thoughts, hours of meditation experience, and age in years as covariates in the analysis did not alter the significance of the results, and yielded similar activation maps for both the thought elaboration > thought dissolution and thought dissolution > thought elaboration contrasts. 54   Figure 3.2. Activation maps for thought elaboration and thought dissolution events. (a) Spontaneous thought elaboration trials (thought elaboration > thought dissolution) were associated with activation in the MPFC, including the RMPFC, DMPFC, VACC, and RACC. (b) Spontaneous thought dissolution trials (thought dissolution > thought elaboration) were associated with activation in the MTL (HPC and PHC), as well as in the right mid-insula (INS), mediodorsal thalamus (THAL), right putamen (PUT), right supramarginal gyrus, right MTG, right STG, and bilateral cerebellum (CBLM). Results are displayed in neurological orientation on the experiment-specific average brain. All activations were significant at p < .05 FWE cluster corrected and k > 20. 55  Table 3.1. Activation peaks for thought elaboration > thought dissolution.    MNI coordinates    Region L/R/M BA x y z Voxels Z value Frontal        Frontopolar cortex (RMPFC) M 10 6 66 4 85 2.49 Superior frontal gyrus (DMPFC) M 9 -8 54 22 151 2.63 Ventral ACC M 32 -12 48 0 64 3.36 Rostral ACC M 32 8 52 12 33 2.42 Note. All activations were significant at p < .05 FWE cluster corrected and k > 20.  56  Table 3.2. Activation peaks for thought dissolution > thought elaboration.   MNI coordinates    Region L/R/M BA x y z Voxels Z value Frontal        Mid-insula R 13 34 6 4 57 3.45 Parietal        Supramarginal gyrus R 40 52 -32 40 76 3.32 Temporal        Hippocampus L 28 -18 -24 -10 100 3.20 Hippocampus R 28 18 -22 -12 149 3.31 Parahippocampus L 36 -14 -34 -10 229 3.50 Superior temporal gyrus R 22 46 -44 14 32 3.09 Middle temporal gyrus R 37 52 -54 -6 79 3.94 Subcortical        Mediodorsal thalamus M - 4 -10 6 303 3.24 Putamen R - 30 -2 6 69 3.42 Dentate of cerebellum M - 6 -54 -34 137 3.09 Anterior cerebellum R - 38 -56 -26 148 3.65 Posterior cerebellum L - -36 -52 -48 131 3.17 Posterior cerebellum R - 30 -54 -44 43 3.33 Note. All activations were significant at p < .05 FWE cluster corrected and k > 20.  57  Time course results To more closely examine how the brain areas that showed relatively increased recruitment during spontaneous thought elaboration trials (thought elaboration > thought dissolution) and during spontaneous thought dissolution trials (thought dissolution > thought elaboration) contributed to the results, percent signal change time courses for ROIs in the MPFC (RMPFC and VACC) and MTL (left HPC and left PHC) were extracted and plotted (Figure 3.3). The MPFC and MTL showed almost no change in activation during spontaneous thought dissolution, which corresponded to the absence of a second thought following an initial thought. However, during spontaneous thought elaboration, which corresponded to the occurrence of a second thought following an initial thought, activation in the MPFC peaked before the button press, whereas activation in the MTL dipped during the button press. 58    Figure 3.3. Time courses during thought elaboration and thought dissolution events. The line graphs represent mean percent signal change over time for each condition in 4-mm radius spheres centered on local maxima from the group-level contrasts (thought elaboration > thought dissolution and thought dissolution > thought elaboration). Event onsets were 4 s before the button press, which is marked by the gray vertical lines. Error bars represent the standard error of the mean. During spontaneous thought elaboration events, when a second thought followed an initial thought, activation in the MPFC (RMPFC and VACC) peaked before the button press, whereas activation in the MTL (HPC and PHC) dipped during the button press. On the other hand, during spontaneous thought dissolution events, when no thought followed an initial thought, the MPFC and MTL showed almost no change in activation. 59  ST-PLS results To identify the neural networks that demonstrated relatively increased recruitment during spontaneous thought elaboration, thought elaboration events were compared to thought dissolution events (thought elaboration > thought dissolution) using ST-PLS. The contrast of thought elaboration trials relative to thought dissolution trials was not significant (p < .066) when all 16 subjects were included. However, the same contrast conducted on 14 subjects that reported more than 5 thought elaboration events was significant with p < .040. The two subjects excluded reported the fewest number of thoughts in total, with one reporting 5 thought elaboration and 14 thought dissolution events, and the other reporting 5 thought elaboration and 10 thought dissolution events.  Relative to spontaneous thought elaboration events, spontaneous thought dissolution events – indicated by negative saliences, or how much a voxel’s increases and decreases in activity were associated with the negatively-weighted or thought dissolution condition (shown in cool colors in Figure 3.4, Table 3.4) – showed greater correlated activity between the MTL (left HPC), mediodorsal thalamus, bilateral head of caudate, left mid-insula, mid-cingulate cortex (MCC), bilateral SMA, and bilateral cerebellum. Relative to spontaneous thought dissolution events, spontaneous thought elaboration events – indicated by positive saliences, or how much a voxel’s increases and decreases in activity were associated with the positively-weighted or thought elaboration condition (shown in warm colors in Figure 3.4, Table 3.3) – showed greater correlated activity between default network areas (MPFC, PCC, and bilateral TPJ), executive network regions (bilateral LPFC), and the bilateral TPC, as well as the MTL (left HPC and bilateral PHC), right ventral lateral thalamus, bilateral putamen, bilateral insula, and bilateral PMA. 60   Figure 3.4. Whole-brain network maps for thought elaboration and dissolution events. During spontaneous thought dissolution events (cool colors), the MTL (left HPC), mediodorsal thalamus, head of caudate, left mid-insula, MCC, SMA, and cerebellum showed correlated activity. On the other hand, during spontaneous thought elaboration events (warm colors), default network areas (MPFC, PCC, and bilateral TPJ), executive network regions (bilateral LPFC), and the bilateral TPC showed correlated activity. Results are displayed in neurological orientation on the experiment-specific average brain and were thresholded using a bootstrap ratio of +/- 1.96 (equivalent to p < .05). Clusters had a spatial extent of at least 50 voxels.  61   Table 3.3. Whole-brain network clusters for thought elaboration > thought dissolution.   MNI coordinates   Region L/R/M BA x y z BSR TRs active Frontal        Frontomarginal gyrus (RMPFC) M 10 16 64 -8 3.22 2, 3*, 4 Medial frontal gyrus (DMPFC) M 9 6 48 28 5.55 2*, 3, 4 Rostral ACC M 32 10 44 0 4.46 2, 3* Middle frontal gyrus (DLPFC) L 9 -42 34 34 5.18 2* Middle frontal gyrus (DLPFC) R 9 48 24 36 4.57 2, 3, 4* Middle frontal gyrus (RLPFC) R 10 34 52 0 4.96 3* Lateral orbital gyrus (VLPFC) L 47 -54 38 -6 3.84 4* Lateral orbital gyrus (VLPFC) R 47 52 46 -8 3.05 4* Anterior insula R 13 32 30 -6 3.34 2, 3*, 4 Mid-insula L 13 -34 6 -6 2.76 3* Posterior insula L 13 -34 -16 2 2.81 4* Posterior insula R 13 36 -20 18 3.83 2*, 3, 4 Premotor area L 6 -36 4 40 3.86 3* Premotor area R 6 40 -16 36 3.99 4* Parietal        Posterior cingulate cortex M 30 -6 -62 12 3.03 3*, 4 Angular gyrus L 39 -40 -70 32 3.83 2*, 3 Supramarginal gyrus L 40 -46 -38 50 3.57 3* Supramarginal gyrus R 40 48 -48 48 3.09 3* 62    MNI coordinates   Region L/R/M BA x y z BSR TRs active Superior parietal lobule L 7 -34 -54 54 3.77 4* Superior parietal lobule R 7 34 -52 52 4.94 3, 4* Temporal         Temporopolar cortex L 38 -56 12 -24 4.51 2*, 3, 4 Temporopolar cortex R 38 30 6 -22 4.48 2*, 3, 4 Hippocampus (head) L 28 -20 -12 -16 4.47 2* Parahippocampus L 36 -30 -12 -30 2.57 3* Parahippocampus R 36 34 -22 -20 3.90 3*, 4 Superior temporal gyrus R 22 48 -20 0 5.04 3*, 4 Occipital        Cuneus L 19 -6 -94 10 6.96 3, 4* Middle occipital gyrus L 18 -18 -92 -4 3.91 2, 3*, 4 Middle occipital gyrus R 18 24 -80 -10 4.67 3*, 4 Subcortical        Putamen L - -24 10 -2 4.19 2* Putamen R - 28 8 0 3.49 2* Ventral lateral thalamus R - 14 -4 -2 4.93 4* Note. For each cluster, the TRs of activation are noted, and the peak of activation (from which the bootstrap ratio and coordinates were taken) is indicated by an asterisk. All clusters had bootstrap ratios (BSR) greater than +/- 1.96 (equivalent to p < .05) and had a spatial extent of at least 50 voxels.  63  Table 3.4. Whole-brain network clusters for thought dissolution > thought elaboration.   MNI coordinates   Region L/R/M BA x y z BSR TRs active Frontal        Mid-insula L 13 -40 2 16 -6.36 2, 3*, 4 Mid-cingulate cortex M 24 -6 4 36 -4.55 3* Supplementary motor area L 6 -8 -4 60 -4.76 2* Supplementary motor area R 6 14 -8 56 -3.68 3* Temporal        Hippocampus (body) L - -16 -34 -8 -3.57 3* Subcortical        Mediodorsal thalamus M - 2 -12 8 -3.60 3*, 4 Head of caudate L - -16 18 16 -3.24 3* Head of caudate R - 16 22 0 -3.55 3*, 4 Anterior cerebellum  L - -32 -68 -28 -3.62 2, 3, 4* Anterior cerebellum R - 28 -62 -20 -4.81 3*, 4 Posterior cerebellum L - -32 -66 -32 -4.23 3* Posterior cerebellum R - 48 -64 -34 -2.97 2*, 3, 4 Note. For each cluster, the TRs of activation are noted, and the peak of activation (from which the bootstrap ratio and coordinates were taken) is indicated by an asterisk. All clusters had bootstrap ratios (BSR) greater than +/- 1.96 (equivalent to p < .05) and had a spatial extent of at least 50 voxels. 64  Discussion Experiment 2 examined which of the brain regions and networks consistently implicated in spontaneous thought contribute specifically to its subsequent elaboration. To do so, the study compared spontaneous thought elaboration events (i.e., when a second thought followed an initial thought) with spontaneous thought dissolution events (i.e., when no thought followed an initial thought). Spontaneous thought elaboration was associated with preferential recruitment of the anterior component of the default network (MPFC), whereas spontaneous thought dissolution was associated with relatively greater activation in MTL memory structures (HPC and PHC). However, extracted time courses revealed that this was due to increased activation in the MPFC and decreased activation in the MTL during spontaneous thought elaboration but almost no change in activation in the MPFC and MTL during spontaneous thought dissolution. In addition, whole-brain network analysis showed that spontaneous thought elaboration corresponded with correlated activity in default network areas (MPFC, TPJ, and PCC), executive network regions (RLPFC and DLPFC), and the TPC, as well as the MTL but only at the beginning. On the other hand, spontaneous thought dissolution corresponded with correlated activity in the MTL and several subcortical relay structures, including the mediodorsal thalamus, head of caudate, and mid-insula. Specifying hours of meditation experience as a covariate of no interest showed recruitment of the same brain networks and regions as the original analyses, suggesting that the results were independent of meditation experience.  Elaborative processing in the MPFC  The recruitment of the MPFC when a second thought followed an initial thought in Experiment 2 suggests it may be central to the subsequent elaboration of spontaneous thought. 65  The ventral MPFC has been linked to the spontaneous appraisal of internally generated states and processes (Andrews-Hanna et al., 2010; Ochsner & Gross, 2008), as well as the processing and assignment of value during decision making (Gottfried, O'Doherty, & Dolan, 2003; Kahnt, Park, Haynes, & Tobler, 2014; Park, Kahnt, Rieskamp, & Heekeren, 2011; Plassmann, O'Doherty, & Rangel, 2010). Meanwhile, the rostral and dorsal MPFC have been associated with explicit reflection on thoughts and emotions related to both the self and others (Amodio & Frith, 2006; Andrews-Hanna et al., 2010; Jenkins & Mitchell, 2011; Lane, Fink, Chau, & Dolan, 1997; Schmitz & Johnson, 2007). In addition, the MPFC has been proposed to support spontaneous, affective forms of evaluative processing during creative thought (Ellamil et al., 2012). The present results thus expand upon a number of previous studies that have linked the MPFC to the first-pass, affective evaluation of self-generated mental content, which may result in the elaboration or continuation of spontaneous thought. Metacognitive processing in the LPFC The standard SPM analysis did not show differential recruitment of the LPFC during spontaneous thought elaboration and spontaneous thought dissolution. However, the PLS whole-brain network analysis showed correlated activity between the LPFC and other regions that may support spontaneous thought elaboration such as the MPFC. This discrepancy may be due to the low power of the univariate SPM analysis to detect effects with a small number of spontaneous thought elaboration events and/or the greater sensitivity of the multivariate PLS analysis.  However, in combination with the results from Experiment 1, the pattern of RLPFC and DLPFC recruitment in Experiment 2 suggests they may contribute to further metacognitive processing, and thus the continuation, of spontaneously generated mental content. This is 66  consistent with previous studies that have linked these regions to intentional, metacognitive evaluation and control functions, such as judgments regarding the occurrence and quality of spontaneous thoughts. For example, the RLPFC has been associated with introspection, or intentionally directing attention towards one’s thoughts (Fleming et al., 2010; McCaig et al., 2011). In addition, the DLPFC has shown activation during the intentional processing of common spontaneous thought content, such as autobiographical plans (Spreng et al., 2010), future event construction (Addis et al., 2007), and theory of mind inferences (Mar, 2011). The RLPFC and DLPFC have also been proposed to support deliberate, analytical forms of evaluative processing during creative thought (Ellamil et al., 2012). However, determining whether the LPFC contributes to the spontaneous elaboration or deliberate evaluation of self-generated thought content remains a task for future research. Suppression of generative processing in the MTL The MTL and MPFC showed correlated activity only at the start of spontaneous thought elaboration but not during spontaneous thought dissolution or during the later stages of spontaneous thought elaboration, when the MTL displayed decreased activity after increased MPFC activity. This pattern of neural recruitment suggests that spontaneous thought elaboration may involve the suppression of MTL activity by the MPFC, which is in line with previous research demonstrating the regulatory (though mostly inhibitory) influence of MPFC regions over MTL functions. For example, spontaneous confabulation, or the involuntary production or recollection of fictitious stories or memories, has been attributed to the MPFC’s unsuccessful suppression of presently irrelevant associations or memories retrieved or constructed by the MTL (Nieuwenhuis & Takashima, 2011; Schacter, Norman, & Koutstaal, 1998; Schnider, 2003; 67  Schnider & Ptak, 1999). In addition, creative production may be facilitated by the minimization of interference between generative processes supported by the MTL and affective evaluative processes supported by the MPFC (Finke, Ward, & Smith, 1992; Gabora, 2010; Howard-Jones & Murray, 2003). This requires engaging in each type of processing separately (e.g., brainstorming or generating ideas while deferring their evaluation) (Basadur, Graen, & Green, 1982; Parnes & Meadow, 1959) and/or alternating between the two types of processing (Ansburg & Hill, 2003; Dorfman, Martindale, Gassimova, & Vartanian, 2008; Rawlings, 1985; Vartanian, Martindale, & Kwiatkowski, 2007). Thus, the flow of spontaneous thought may depend on the regulation or inhibition of MTL generative processes by MPFC evaluative regions (via subcortical relay structures such as the thalamus and basal ganglia), leading to the continuation of current thought content and/or hindering the development of new thought content. Intermediary spontaneous thought processes In Experiment 2, the finding that the PCC did not display increased activation when a second thought followed an initial thought suggests that it may not be central to the elaboration of spontaneous thought. By contrast, in Experiment 1, the PCC showed early recruitment during spontaneous thought along with the MTL and before the MPFC and LPFC, suggesting that it may contribute to the generation of spontaneous thought. However, whole-brain network analysis in Experiment 1 revealed that PCC activity did not correlate with initial MTL recruitment but correlated with later MPFC and LPFC activity. Thus, it is possible that PCC activation is not specific to either the generation or elaboration of spontaneous thought.  The pattern of PCC recruitment in Experiments 1 and 2 suggests that the PCC may instead facilitate switching between the generative and elaborative components of a larger neural 68  network that supports spontaneous thought. This is consistent with proposals stating that the PCC transfers information between neural systems that support bottom-up processing of salient externally and internally generated information (e.g., MTL) and other systems supporting top-down processes that attach meaning to and modulate such bottom-up processes (e.g., MPFC) (Andrews-Hanna et al., 2010; Leech et al., 2012; Vogt & Laureys, 2005). Using a faster fMRI data acquisition sequence (e.g., TR < 2 s) and other neuroimaging modalities in future studies may enable the examination of whether the PCC is indeed engaged after MTL generative processes but before MPFC elaborative processes during spontaneous thought flow. Similarly, the finding that the TPC did not display increased activation when a second thought followed an initial thought in Experiment 2 suggests that it may not be central to the elaboration of spontaneous thought. However, in Experiment 1, the TPC showed late recruitment during spontaneous thought along with the MPFC and LPFC and after the MTL, suggesting that it may contribute to the elaboration of spontaneous thought. In addition, whole-brain network analysis in Experiment 1 revealed that TPC activity did not correlate with initial MTL recruitment but correlated with later MPFC and LPFC activity. Thus, it is not clear whether or not TPC activation supports the elaboration of spontaneous thought. The pattern of TPC recruitment in Experiments 1 and 2 suggests that the TPC may instead support lower-level visceroceptive and/or conceptual elaborative processes that occur between the initial generation and subsequent elaboration of spontaneous thought. As previously mentioned, the TPC has been proposed to bind output from memory processes (e.g., from the MTL) and complex perceptual input (e.g., from the TPJ) to visceral, emotional input from the anterior insula and amygdala (Olson et al., 2007). However, the TPC has also been proposed to integrate conceptual knowledge from semantic memory with autobiographical details from 69  episodic memory during memory retrieval (Graham et al., 2003). During spontaneous thought, the TPC may thus support additional visceroceptive and conceptual processing of MTL output before relaying the information to the MPFC for higher-level elaborative processing. Using a faster fMRI data acquisition sequence (e.g., TR < 2 s) and other neuroimaging modalities in future studies may allow the assessment of whether the TPC is recruited after MTL generative processes but before MPFC elaborative processes during spontaneous thought flow.  Although many questions remain, information about the occurrence and progression of spontaneous thoughts collected in Experiments 1 and 2 helped to reveal the temporal dynamics of neural recruitment during spontaneous thought flow. It also helped to reveal the distinct functional contributions of the various brain regions and networks consistently implicated in spontaneous thought. However, it remains to be investigated if real-time activity changes in these brain regions and networks reflect actual spontaneous thought dynamics. Thus, a third exploratory experiment was conducted to examine whether the occurrence of spontaneous thought could be predicted by real-time fluctuations in the activity of one of these brain regions.  70  CHAPTER 4 – EXPERIMENT 3: REAL-TIME FMRI EXPERIENCE SAMPLING Information about the occurrence and progression of spontaneous thoughts collected in Experiments 1 and 2 helped to provide empirical support for the theorized sequence of neural processes during spontaneous thought flow. It also helped to reveal a more detailed account of how various brain regions and networks contribute to the generation and elaboration of spontaneous thoughts. However, it remains to be investigated if real-time activity changes in brain regions frequently associated with spontaneous thought reflect actual spontaneous thought dynamics. Thus, a third exploratory experiment aimed to examine whether the occurrence of spontaneous thought could be predicted by real-time fluctuations in the activation level of a particular brain region.  Recent technological advances in fMRI data acquisition and processing have led to the development of real-time fMRI, which allows brain activation to be observed during the scanning session and thus has been used to provide neurofeedback in fMRI training procedures (deCharms, 2007, 2008). However, in Experiment 3, real-time fMRI was used instead to deliver probes for spontaneous thought occurrence based on the level of activity in the right anterior hippocampus (RAH). This approach enabled the examination of whether activity in a certain brain region (e.g., RAH) is associated with a particular cognitive process (e.g., spontaneous thought), providing a more direct test of the causal link between brain recruitment and mental experience compared to delivering thought probes at random, predetermined time points. In addition, subjects reported their mental experience at the time of the probes using an MRI-compatible writing tablet (Tam, Churchill, Strother, & Graham, 2010), which allowed the collection of more detailed subjective information during fMRI scanning compared to a series of button presses or offline verbal interviews.  71  The RAH has been associated with increased recruitment during the construction of mental simulations, especially about future events (e.g., Addis et al., 2009; Addis et al., 2007; Weiler et al., 2010), which form a large part of spontaneous thought content (Smallwood et al., 2009). It has also shown increased activation during creative idea generation (Ellamil et al., 2012) and spontaneous thought generation (as in Experiment 1). Thus, it was predicted that probing during high levels of activity in the RAH would be associated with more reports of spontaneous thoughts compared to probing during low levels of activity in the RAH. Methods Subjects Five subjects (after 1 exclusion; 4 male and 1 female; M = 53.63 years old, SD = 3.08, range = 50.17 – 58.49) from Experiment 1 also participated in Experiment 3. Due to a host of technical issues with the MRI scanner and real-time fMRI software, we were only able to collect data from 5 out of the 10 subjects that were recruited for Experiment 3. One subject was excluded from the analyses because the experiment software did not record her responses.   The subjects were long-term, expert mindfulness meditators with more than 3,000 hours of lifetime meditation experience and at least 1 hour of daily practice in the Mahasi Vipassana tradition (M = 12,578.60 hours, SD = 9,147.62, range = 3,174 – 23,700). The same meditation experience questionnaire (Appendix A) and phone interview procedures as in Experiment 1 were administered to ensure consistency of the meditation technique across subjects and attainment of extensive knowledge of and experience with the meditation technique through regular practice and attendance of several long-term intensive retreats. The subjects were recruited from Vipassana meditation communities in Vancouver (BC, Canada), Vancouver Island (BC, 72  Canada), Boulder (CO, USA), San Francisco (CA, USA), and Seattle (WA, USA).  All subjects had normal or corrected-to-normal vision with no MRI contraindications or current psychiatric medication use. Four were right-handed and one was left-handed, and all used their dominant hand to write their responses during the experiment. All protocols were approved by the UBC Clinical Research Ethics Board and the UBC MRI Research Center. All subjects gave informed written consent prior to participating and received payment as compensation. Real-time fMRI data acquisition Functional and structural MRI data were collected using a 3.0 Tesla Philips Intera MRI scanner (Best, Netherlands) with a standard head coil. Head movement was restricted using foam padding around the head. T2*-weighted functional images were acquired parallel to the AC/PC line using a single-shot gradient EPI sequence (TR = 1 s, TE = 30 ms, FA = 90°, FOV = 240 × 240 × 132 mm, matrix size = 80 × 78, SENSE factor = 1.0). A total of 610 functional volumes were acquired for each run, each including 19 interleaved axial slices (6 mm thick with 1 mm skip) covering the entire brain. Before functional imaging, an inversion recovery prepared T1-weighted structural volume was acquired in the same slice locations and orientation as the functional images using a fast spin-echo sequence (TR = 2 s, TE = 10 ms, FA = 90°, FOV = 240 × 240 × 132 mm, acquisition matrix size = 256 × 255, reconstructed matrix size = 512 × 512, IR = 800 ms, spin-echo turbo factor = 5). Task procedure  As in Experiments 1 and 2, one to two days prior to the actual scanning session, subjects engaged in a practice session identical to the actual scanning procedure in a mock scanner environment to become acclimatized to the task, writing tablet, and scanner noises. While 73  viewing a gray fixation cross on a black background, subjects carefully but non-reactively observed thoughts that arose until they changed or disappeared and then returned their attention back to their breath (Sayadaw, 1985, 2002). Thoughts were defined as mental events that took attention away from or became more prominent in attention than the breath during mindfulness meditation. Whenever the screen flashed white for 500 ms, subjects used a custom-built MRI-compatible writing tablet (Tam et al., 2010) to briefly describe their mental experience just before the flash or probe. To signal that they had finished writing, subjects drew a line across the bottom of the screen. If the subjects did not have thoughts to report, they simply drew a line across the screen. Immediately after a line was drawn, the subjects resumed their meditation while the screen was cleared and the gray fixation cross on a black background was displayed again. (See Appendix B for the complete task instructions.) Three subjects completed two 10-minute task runs, one subject completed 3 task runs, and one subject completed 1 task run. The task was implemented and presented using E-Prime 2.0 (Psychology Software Tools, Sharpsburg, PA).  Real-time fMRI procedure  During the scanning session, the real-time fMRI analysis computer communicated with the MRI scanner through custom-built software developed in C and C++, which reconstructed BOLD contrast images with approximately a 1 s delay following acquisition (Figure 4.1a) (McCaig et al., 2011). The ROI – the RAH (Figure 4.1b) – was localized using anatomical landmarks, which were referenced from the Duvernoy Human Brain Atlas (Duvernoy, 1999). The RAH was identified on each subject’s unprocessed, high-resolution structural images acquired prior to the functional task runs, and was then interpolated onto the corresponding slices 74  of the subject’s sample functional volume. A “negative” mask, which included all brain voxels except for the target ROI, was generated and used to control for global modulation effects. Signal from the individually localized ROI and negative mask was motion corrected, extracted, averaged, and temporally filtered (first-order band-pass, 0.0125Hz – 0.08Hz) to produce continuously updated (every 1 s) time courses for the ROI and negative mask.  The first 60 s of each 10-minute task run, during which no probes were delivered, was used to obtain initial measures of the means and standard deviations of activity levels in the ROI and negative mask. For the remainder of the task run, fluctuations in activity levels in the ROI and negative mask were calculated as the number of standard deviations (S) above or below their corresponding mean activations, based on the continuously updated (every 1 s) means and standard deviations from the current task run. Thought probes were represented by 500 ms white screen flashes, which prompted the subjects to briefly describe their mental experience just before the probes using the writing tablet. Thought probes were triggered when the RAH showed high activity (SROI > 1) or low activity (SROI < –1) for at least 3 s. However, no thought probes were delivered when the negative mask or global signal also showed high (SNEG > 1) or low (SNEG < –1) activity because it meant that the activity change was not specific to the RAH. In addition, no thought probes were delivered 30 s after the previous thought probe. Comparing the number of spontaneous thought reports during high-activity and low-activity probes allowed the examination of whether real-time fluctuations in RAH activity could predict the occurrence of spontaneous thought. 75   Figure 4.1. Real-time fMRI display viewed by the experimenter during scanning. (a) The main upper panel showed the levels of activation in the target ROI (i.e., the RAH, in blue) and the negative mask (i.e., the rest of the brain, in green). The bottom panel showed fluctuations in activity levels in the ROI and negative mask, which were calculated as the number of standard deviations (S) above or below their corresponding mean activations, based on the continuously updated (every 1 s) means and standard deviations from the current task run. The upper-left panel showed a fluctuating line that displayed whether activation in the ROI was above (i.e., SROI > 1, in pink in the top-right quadrant) or below (i.e., SROI < -1, in pink in the bottom-left quadrant) the threshold for triggering thought probes. Blue lines were displayed when ROI activation did not pass the threshold, and yellow lines were displayed when the negative mask also showed high (SNEG > 1) or low (SNEG < –1) activation. (b) The ROI – the RAH – was localized using anatomical landmarks, which were referenced from the Duvernoy Human Brain Atlas. The RAH was identified on each subject’s unprocessed, high-resolution structural images acquired prior to the functional task runs, and was then interpolated onto the corresponding slices of the subject’s sample functional volume. a) b) 76  Offline fMRI data analysis Data for Experiment 3 were preprocessed and analyzed using the same SPM8 procedures as in Experiment 1. In Experiment 3, the regressor functions were constructed to model each of the events (i.e., highthought, highno-thought, lowthought, and lowno-thought) and were compared using pairwise contrasts for each subject. Onsets for the high-activity and low-activity events were specified at 4 s before the corresponding probe display times. Because of the small sample size, group fixed-effects analyses were performed for each contrast. The resulting T maps were transformed to the unit normal Z distribution to create a statistical parametric map for each contrast. The threshold for significance was set at p < 0.001 uncorrected and extent threshold k > 20 voxels. Results Behavioral results Thought probes were delivered an average of 13.00 times (SD = 7.81) throughout all scanning sessions with an average of 6.50 probes (SD = 1.43) per task run. To determine if probing during increased RAH activity resulted in more reports and different qualities of spontaneous thought than probing during decreased RAH activity, the number and type of spontaneous thought reports and no-thought reports during high-activity and low-activity probes were compared for each subject (Table 4.1, Figure 4.2). Instances of no thought were defined as reports containing only a line across the screen as per the task instructions, whereas the rest of the reports were counted as instances of spontaneous thought. After the scanning sessions, without knowing the study’s hypotheses or which conditions (i.e., probe types) their thought reports belonged to, the subjects were asked to describe their reports in more detail and any 77  patterns they saw between one set of reports (i.e., during high RAH activity) and another set (i.e., during low RAH activity).    Subject 1 described events before high-activity probes as “primarily visual and narrative” (e.g., thinking about a “previous meeting,” “[future] Dhamma talk,” and “[future] experiment”), whereas events before low-activity probes were “mainly somatic with a little narrative” (e.g., noticing “the heart beating” and “a pressure in the chest”). Subject 2 noted that events before high-activity probes were “[mental commentary] about present…stimuli [and] planning for an…action” (e.g., thinking about “the [fixation] cross starting to look like Gumby,” “the sound of the scanner and likening it to music,” and “inviting [a person] afterwards for a beer or dinner”), whereas events before low-activity probes were “telling [him]self what to do [regarding the meditation]” (e.g., thinking about “concentrating back on the breath” and being “attentive to everything in the here and now”). Subject 3, however, did not offer to describe patterns in her thought reports, but she appeared to report more narrative thoughts before high-activity probes (e.g., “reminding [her]self to…[focus] on meditation” and “remembering the sensation [she] experienced…earlier”) and more body sensations before low-activity probes (e.g., “noting the sensation of vibration in [her] leg” and “noticing the noise and the process of hearing”). Subject 4 observed that events before high-activity probes “involv[ed] thinking [but] the awareness of thinking was weak or almost non-existent until the prompt/probe” (e.g., “remembering painful experience at lab” and “thinking about the word non-ferrous magnetic”), whereas events before low-activity probes were “about the awareness of events only” (e.g., “awareness of physical sensations” and “awareness of an emotional event”). Subject 5 also did not offer to describe patterns in his thought reports, but he appeared to report more present-centered focus before low-activity probes (e.g., “feeling absorbed,” “feeling blissful,” and “feeling that [he] was in flow 78  state”) than before high-activity probes (e.g., “thinking [he’d] like to drink some coffee” and “thinking something about electronics”).  Thus, it appears that for subjects increased RAH activity and decreased RAH activity were associated with different qualities, but not necessarily different quantities, of spontaneous thought events (Figure 4.3). Increased RAH activity seemed to correspond to thoughts with a meaning-making focus (i.e., narrative, temporally-extended, and conceptual), whereas decreased RAH activity seemed to correspond to thoughts with a present-centered focus (i.e., experiential, immediate-moment, and sensory/emotional). However, the small sample size and number of thought probes did not allow formal statistical comparisons of the number and quality of spontaneous thought and no-thought reports during high and low RAH activity (e.g., two-way repeated measures ANOVA). 79  Table 4.1. Individual thought reports during high-activity and low-activity probes.  Subject 1: High RAH Activity Subject 1: Low RAH Activity Visual-Narrative Thought Somatic-Narrative Thought Visual-Narrative Thought Somatic-Narrative Thought Previous meeting with my  practicum supervisors  Clinic where my practicum is Some tension and need to relax parts of the body Dhamma talk I have given or will give  Presentation Heart beating and slight tension in the area Need to take a deep breath in  Triviality of most of human activity Pressure in the chest Discussion…with my supervisor regarding client participation and buy-in at the clinic  Ten more minutes Pressure in the chest area or pressure in the voice Discussion…in the MRI control room  Dad Heart racing Participation in an MRI experiment…later this summer  Eyepiece Bowel    Butterfly      Subject 2: High RAH Activity Subject 2: Low RAH Activity Mental Commentary and Planning Present-Centered Focus Mental Commentary and Planning Present-Centered Focus Inviting…afterwards for a beer or dinner to catch up Feeling of joy  Strong feelings of joy and metta Cross is starting to look like Gumby and finding it funny   Calm down by concentrating back on the breath Sound of the scanner and likening it to music   Being present and attentive to everything in the here and now Cross looks like a little bird flying overhead        Subject 3: High RAH Activity Subject 3: Low RAH Activity Narrative Thought Body Sensation Narrative Thought Body Sensation Reminding myself to settle down and focusing on meditation Noting the hearing sensation  Keeping track of different body sensations…some vibration in my left calf, coolness on my hand Remembering the sensation I experienced a few minutes earlier   Noting the sensation of vibration in my leg    Noticing the noise and the process of hearing 80  Subject 4: High RAH Activity Subject 4: Low RAH Activity Thought without Awareness Thought with Awareness Thought without Awareness Thought with Awareness Remembering painful experience at lab  Visual perception plus mental commentary… concepts of shadow, cross, and screen ‘Exhale’ is awareness of physical sensations Thinking about the word ‘non-ferrous magnetic’   ‘Inhale” is awareness of physical sensations    ‘Aversion’ is awareness of an emotional event     Subject 5: High RAH Activity Subject 5: Low RAH Activity Mental Commentary and Planning Present-Centered Focus Mental Commentary and Planning Present-Centered Focus Thinking I'd like to drink some coffee Feeling relaxed Remembered something Feeling blissful Thinking something about electronics  Remembered something Feeling that I was in flow state    Feeling fatigued    Feeling absorbed      81   Figure 4.2. Individual thought reports during high-activity and low-activity probes. The bar graphs represent the number of spontaneous thought and no-thought reports during high RAH and low RAH activity for individual subjects. Based on the subject-specified thought categories, it appears that increased RAH activity and decreased RAH activity were associated with different qualities, but not necessarily different quantities, of spontaneous thought events. Increased RAH activity seemed to correspond to thoughts with a meaning-making focus (i.e., narrative, temporally-extended, and conceptual), whereas decreased RAH activity seemed to correspond to thoughts with a present-centered focus (i.e., experiential, immediate-moment, and sensory/emotional). 82          Figure 4.3. Averaged thought reports during high-activity and low-activity probes. The bar graphs represent the mean number of spontaneous thought and no-thought reports during high RAH and low RAH activity across subjects. Error bars represent the standard error of the mean. (a) High or low RAH activity did not appear to predict the occurrence or absence of spontaneous thought, (b) but might instead correspond to different qualities of spontaneous thought (i.e., meaning-making versus present-centered).  83  SPM results  To identify the brain regions that demonstrated relatively increased recruitment along with increased RAH activation during spontaneous thought, thought events during high RAH activity probes were compared to thought events during low RAH activity probes (highthought > lowthought). There was greater activation during spontaneous thought when RAH activity was high (Figure 4.4a, Table 4.2) in the PCC / precuneus (BA 31; peak x, y, z = -2, -58, 34) and left TPJ (BA 39; peak x, y, z = -56, -62, 20). Other increases in activation were observed in the left VLPFC (pars opercularis), left DLPFC, right posterior insula, bilateral superior parietal lobule (SPL), bilateral middle occipital gyrus (MOG), bilateral middle temporal gyrus (MTG), left fusiform gyrus, right inferior temporal gyrus (ITG), and bilateral cerebellum.           To identify the brain regions that demonstrated relatively increased recruitment along with decreased RAH activation during spontaneous thought, thought events during low RAH activity probes were compared to thought events during high RAH activity probes (lowthought > highthought). There was greater activation during spontaneous thought when RAH activity was low (Figure 4.4b, Table 4.3) in the RMPFC (BA 10; peak x, y, z = 2, 56, 20), left RLPFC (BA 10; peak x, y, z = -18, 64, 20), and right RLPFC (BA 10; peak x, y, z = 32, 64, -2). Other increases in activation were observed in the right VLPFC (pars orbitalis), bilateral posterior insula, right postcentral gyrus (S2), bilateral supplementary motor area (SMA), right premotor area (PMA), left inferior temporal gyrus (ITG), left transverse temporal gyrus (A1), and vermis of cerebellum. Thus, spontaneous thought during high RAH activity corresponded with increased engagement of brain areas associated with initial spontaneous thought generation in Experiment 1 (e.g., PCC and TPJ). In contrast, spontaneous thought during low RAH activity corresponded with 84  preferential recruitment of brain areas associated with subsequent spontaneous thought elaboration in Experiment 2 (e.g., MPFC and LPFC). 85   Figure 4.4. Activation maps for thought events during high and low RAH activity. (a) Spontaneous thought events during high RAH activity (highthought > lowthought) were associated with activation in the PCC / precuneus (PREC) and left TPJ. Activations were also observed in the left VLPFC (pars opercularis), SPL, MOG, MTG, right ITG, and cerebellum (CBLM). (b) Spontaneous thought events during low RAH activity (lowthought > highthought) were associated with activation in the MPFC and RLPFC. Activations were also observed in the posterior insula (INS), postcentral gyrus (S2), SMA, and left ITG. Thus, spontaneous thought during increased RAH activation was associated with the recruitment of brain regions previously implicated in the generation of spontaneous thought in Experiment 1. In contrast, spontaneous thought during decreased RAH activation was associated with the recruitment of brain areas that may support the elaboration of spontaneous thought from Experiment 2. Results are displayed in neurological orientation on the experiment-specific average brain. All activations were significant at p < .001 uncorrected and k > 20. 86  Table 4.2. Activation peaks for thought events during high RAH activity (highthought > lowthought).   MNI coordinates   Region L/R/M BA x y z Voxels Z value Frontal        Inferior frontal gyrus  (pars opercularis)  L 44 -48 20 18 530 5.36 Middle frontal gyrus (DLPFC) L 9 -18 36 48 45 4.23 Posterior insula R 13 48 -12 4 74 5.54 Parietal        Angular gyrus L 39 -56 -62 20 123 4.45 PCC / Precuneus M 31 -2 -58 34 960 5.74 Superior parietal lobule M 7 0 -74 44 32 4.25 Temporal        Fusiform gyrus L 37 -38 -42 -20 377 4.45 Inferior temporal gyrus R 21 40 4 -26 95 4.85 Middle temporal gyrus L 21 -62 -44 -2 46 3.86 Middle temporal gyrus R 21 62 -44 0 96 3.97 Occipital        Middle occipital gyrus L 18 -4 -82 -12 1684 6.12 Middle occipital gyrus R 18 14 -76 -8 210 5.01         87    MNI coordinates   Region L/R/M BA x y z Voxels Z value Subcortical        Anterior cerebellum L - -48 -70 -22 78 4.69 Anterior cerebellum R - 26 -72 -30 311 4.22 Posterior cerebellum L - -36 -58 -50 195 4.70 Note. All activations were significant at p < .001 uncorrected and k > 20.  88  Table 4.3. Activation peaks for thought events during low RAH activity (lowthought > highthought).   MNI coordinates   Region L/R/M BA x y z Voxels Z value Frontal        Superior frontal gyrus (RMPFC) M 10 2 56 20 121 5.23 Middle frontal gyrus (RLPFC) L 10 -18 64 20 43 4.11 Middle frontal gyrus (RLPFC) R 10 32 64 -2 288 5.58 Inferior frontal gyrus  (pars orbitalis)  R 47 42 32 -14 151 4.69 Posterior insula L 13 -44 -14 -4 109 5.10 Posterior insula R 13 48 -6 -8 45 3.84 Supplementary motor area M 6 0 -2 52 210 5.41 Premotor area R 6 38 0 32 103 4.01 Parietal        Postcentral gyrus (S2) R 43 62 -8 18 122 4.19 Temporal        Inferior temporal gyrus L 20 -44 -8 -32 331 5.01 Transverse temporal gyrus L 41 -48 -22 12 119 4.77 Subcortical        Vermis of cerebellum M - -6 -76 -48 90 4.57 Note. All activations were significant at p < .001 uncorrected and k > 20.  89  Discussion Experiment 3 examined whether the occurrence of spontaneous thought could be predicted by real-time fluctuations in the activation level of a particular brain region. To do so, the study compared online, written thought reports when activity in the right anterior hippocampus (RAH) was high and when it was low as determined by real-time fMRI software. The level of RAH activity did not appear to predict the occurrence or absence of spontaneous thoughts. However, high RAH activity seemed to correspond to thoughts with a meaning-making focus (i.e., narrative, temporally-extended, and conceptual), whereas low RAH activity seemed to correspond to thoughts with a present-centered focus (i.e., experiential, immediate-moment, and sensory/emotional). Thus, the level of RAH activity may reflect different qualities, but not necessarily different quantities, of spontaneous thought. In addition, spontaneous thought reports during high RAH activity were associated with preferential recruitment of the PCC and TPJ, which were also engaged during the generation of spontaneous thoughts in Experiment 1. In contrast, spontaneous thought reports during low RAH activity were associated with preferential recruitment of the MPFC and LPFC, which were also engaged during the elaboration of spontaneous thoughts in Experiment 2. Meaning-making and present-centered spontaneous thought processes Increased MTL activity, specifically in the RAH, along with recruitment of the PCC and TPJ appeared to correspond to spontaneous thoughts with a meaning-making focus. These narrative, temporally-extended, and conceptual thoughts included remembering past events, planning future events, and linking concepts to incoming sensory information. This pattern of neural recruitment is consistent with results from Experiment 1, which suggested an important 90  role for the MTL, PCC, and TPJ in spontaneous thought generation. Thus, the MTL, PCC, and TPJ may contribute to the generation of spontaneous thought content via meaning-making processes, such as the retrieval and recombination of stored associations and details to construct episodic simulations of past, future, or novel events (e.g., Buckner et al., 2008; Cabeza et al., 2008; Schacter & Addis, 2009).  In contrast, decreased MTL activity along with recruitment of the RMPFC and RLPFC appeared to correspond to spontaneous thoughts with an experiential, present-centered focus. These included thoughts related to body sensations and emotions, as well as awareness of and absorption in the current mental experience. This pattern of neural recruitment is consistent with results from Experiment 2, which suggested the suppression of MTL activity by the MPFC during spontaneous thought elaboration. However, it appears to contradict the proposed roles of the MPFC and LPFC in the subsequent affective evaluation and further metacognitive processing, respectively, of spontaneously generated thought content in Experiments 1 and 2. Nonetheless, it has been suggested that such affective evaluation is supported by the VMPFC, which has been linked to the spontaneous appraisal of internally-generated information (e.g., Andrews-Hanna et al., 2010; Ochsner & Gross, 2008). Experiment 3, in contrast, showed recruitment of the RMPFC, which has been linked to explicit reflection on self-generated mental content (e.g., Andrews-Hanna et al., 2010; Jenkins & Mitchell, 2011). In addition, the RLPFC has been associated with introspection, or intentionally directing attention towards one’s thoughts (e.g., Fleming et al., 2010; McCaig et al., 2011). Thus, the RMPFC and RLPFC may support the regulation of spontaneous thought flow in order to maintain present-centered focus via the monitoring of mental experiences and the suppression of meaning-making retrieval and associative processes. 91  Thought probe thresholds The absence of correspondence between spontaneous thought occurrence and RAH activation may reflect limitations in how the experience sampling probes were delivered. The lack of differential RAH recruitment in the offline fMRI analysis between spontaneous thoughts reported during high RAH activity and those reported during low RAH activity suggests that the threshold for delivering thought probes was too low to detect actual changes in RAH activation and thus predict spontaneous thought occurrence. Increasing the threshold for delivering thought probes might reduce noise in the responses collected and better reflect standard, offline measures of brain activity fluctuation. However, a more stringent threshold would further decrease the number of responses collected and thus the ability to perform meaningful behavioral and fMRI statistical analyses of the data. In addition, with the delay in the BOLD response (Buxton & Frank, 1997; Hu, Le, & Ugurbil, 1997), it is possible that by the time increased RAH activation had been registered by the real-time fMRI software and had triggered a thought probe, the corresponding spontaneous thought had already passed. It might be useful for future studies to train and instruct subjects to report their mental experience further back in time than just prior to the thought probe. Moreover, based on the little change in MTL (including the RAH) activation when no thought followed an initial spontaneous thought in Experiment 2, delivering three types of probes – high activity, low activity, and no activity change – might enable better prediction of spontaneous thought occurrence than using only two types of probes. Both high and low RAH activity might be associated with more instances but different qualities of spontaneous thought, whereas no activity change in the RAH might be associated with fewer instances of spontaneous thought. 92  Region of interest definitions  The inability to predict spontaneous thought occurrence based on real-time fluctuations in RAH activity may also stem from limitations in how the ROI was defined. Although the MTL (including the RAH) has been repeatedly implicated in the generation phase of several cognitive processes, such as episodic memory (e.g., Addis et al., 2007), creative thinking (e.g., Ellamil et al., 2012), and spontaneous thought (e.g., Experiment 1), it certainly does not act in isolation. In light of the increased MTL, TPJ, and PCC recruitment during spontaneous thought generation in Experiment 1, using activation information from these regions simultaneously to determine when thought probes are delivered might allow better prediction of spontaneous thought occurrence compared to using activation information from only the RAH. Furthermore, based on increased MPFC recruitment during spontaneous thought elaboration in Experiment 2, using activation information from the MPFC to trigger thought probes might enable prediction of the later stages of spontaneous thought flow. Alternatively, functional connectivity or multi-voxel pattern analysis techniques could be used to provide network-related activity measures, rather than simply averaging activations over multiple voxels and regions, for better sensitivity to and prediction of such subtle and transient cognitive processes. The challenge would then be to adapt correlation measures and pattern classification algorithms for implementation during real-time fMRI processing without introducing delay. Subject-specified response categories  Finally, the pattern of responses described by the subjects points to the value of using first-person data to detect and interpret neural processes. Although the occurrence of spontaneous thought could not be predicted by real-time changes in RAH activation, the detailed, 93  free-form, first-person reports of thought processes collected enabled a more specific and informed method of classifying and analyzing cognitive and neural responses compared to strictly experimenter-determined conditions. Indeed, using electroencephalogram (EEG), one previous study found distinct patterns of brain activity between trials for a three-dimensional illusion task, which were categorized according to the subjects’ level of readiness extracted from their first-person verbal reports (Lutz, Lachaux, Martinerie, & Varela, 2002). The use of real-time fMRI experience sampling in combination with subject-determined response categories would allow a more direct test of the causal link between brain activation and subjective experience, as well as better spatial localization of brain activation, compared to the aforementioned study. In addition, the response categories identified by experienced meditators, who are better able to monitor the occurrence and progression of mental events than non-meditators, could help determine the types of experience sampling probes to use in future studies with both meditator and non-meditator subjects. Thus, the detailed, free-form, introspective data collected in the present experiment provide valuable information for the development of future real-time and standard fMRI experience sampling procedures to further examine the neural correlates of spontaneous thought.  94  CHAPTER 5 – GENERAL DISCUSSION Summary of main findings The present dissertation investigated the neural basis of spontaneous thought processes by integrating first-person reports from expert mindfulness meditators with third-person neural measures from fMRI experience sampling procedures. Experiment 1 examined the temporal dynamics of brain activity during spontaneous thought generation by comparing subject- or self-caught spontaneous thought events with prompted, deliberate thought events (i.e., processing words of the same type as the thoughts that were reported). Time courses of brain activation and temporal patterns of neural network recruitment revealed that MTL memory structures (HPC and PHC) were recruited first, followed by default network areas (especially the MPFC) and then executive network regions (especially the LPFC). These results suggest the engagement of different levels of generative and elaborative processing during the flow of spontaneous thought.  Experiment 2 examined which brain regions contributed specifically to spontaneous thought elaboration and to spontaneous thought dissolution. To do so, the experiment compared spontaneous thought elaboration events (i.e., when a second thought followed an initial thought) with spontaneous thought dissolution events (i.e., when no thought followed an initial thought). Spontaneous thought elaboration was associated with preferential recruitment of the anterior component of the default network (MPFC) and decreased activation of MTL memory structures (HPC and PHC). Spontaneous thought elaboration may thus engage affective evaluation processes while suppressing associative generation processes. Spontaneous thought dissolution, on the other hand, was associated with almost no change in activation in the MTL and MPFC. Spontaneous thought dissolution may thus reflect the return of generative and elaborative neural processes back to baseline levels of activation.  95  Experiment 3 examined whether the occurrence of spontaneous thought could be predicted by real-time fluctuations in the activation of the right anterior hippocampus (RAH). To do so, the experiment compared online, written thought reports when RAH activity was high and when it was low as determined by real-time fMRI software. The level of RAH activity did not appear to predict the occurrence or absence of spontaneous thoughts. However, high RAH activity was associated with thoughts containing a meaning-making focus (e.g., remembering, planning, and linking concepts), whereas low RAH activity was associated with thoughts containing a present-centered focus (e.g., body sensations, emotions, awareness, and concentration). In addition, the predominantly meaning-making thoughts reported during high RAH activity were associated with preferential recruitment of the PCC and TPJ, which were also engaged during spontaneous thought generation in Experiment 1. Meanwhile, the largely present-centered thoughts reported during low RAH activity were associated with preferential recruitment of the MPFC and LPFC, which were also engaged during spontaneous thought elaboration in Experiment 2. The level of RAH activity may thus reflect different qualities, but not necessarily different quantities, of spontaneous thought. Contributions and neuroscientific implications The integration of first-person reports from individuals with great introspective expertise (i.e., highly experienced mindfulness meditators) with third-person neural measures from fMRI experience sampling procedures revealed a number of novel findings about neural recruitment during spontaneous thought. First, compared to previous studies, results from the present experiments reflected neural recruitment more specific to spontaneous thought processes. Second, the present results provided empirical support for the hypothesized sequence of neural 96  processes during spontaneous thought. Third, the sequence of neural processes during spontaneous thought identified in the present experiments helped to distinguish the functional contributions of the various brain regions consistently implicated in spontaneous thought to its component processes. Finally, the progression of neural recruitment during spontaneous thought elaboration revealed in the present experiments showed that the flow of spontaneous thought may depend on the regulation of MTL generative processes by MPFC evaluative regions. Neural recruitment specific to spontaneous thought Compared to previous studies, results from the present experiments reflected neural recruitment more specific to spontaneous thought processes. Because most previous studies of spontaneous thought did not ask subjects about their mental experience during resting state sessions (e.g., D'Argembeau et al., 2005; Gorgolewski et al., 2014; Kucyi & Davis, 2014), it was not clear how much and when spontaneous versus deliberate thoughts occurred during the experiments. Thus, the reported brain activations might have corresponded to a combination of spontaneous and deliberate mental processes. Moreover, although some studies of spontaneous thought had asked subjects about their mental experience during resting state sessions (e.g., Tusche et al., 2014), subjects were only asked about the content of their thoughts and not whether their thoughts were spontaneous or deliberate. Thus, it was difficult to determine whether the reported brain activations represented spontaneous mental processes or simply thought content. The comparison of subject- or self-caught spontaneous thought events with prompted, deliberate thought events (i.e., processing words of the same type as the thoughts reported) in the present experiments enabled a more stringent assessment of neural recruitment during spontaneous thought. This more specific information about neural recruitment during 97  spontaneous thought could help in the development of future studies to examine why brain regions that support deliberate, goal-directed cognitive processes are sometimes activated along with brain regions that contribute to spontaneous, undirected mental processes (e.g., the amount of intentional or effortful processing a thought involves).       Sequence of neural processes during spontaneous thought One of the key findings of the present work is the precise sequence of neural recruitment during spontaneous thought flow, which was revealed using temporal data collected during the occurrence and progression of spontaneous mental events. Because the onset and development of spontaneous thoughts were not directly assessed in past neuroimaging studies, it was previously difficult to determine whether the brain regions frequently associated with spontaneous thought were engaged simultaneously and/or consistently during periods of spontaneous thought. The examination of the temporal progression of brain activation and neural network recruitment during spontaneous thoughts in the present experiments showed important differences in the timing with which these brain regions and networks were engaged. The temporal dynamics of neural recruitment identified may correspond to the different levels of processing involved in spontaneous thought, as well as the flow or transfer of information between brain regions and networks associated with spontaneous thought. Instead of a single, homogenous process, spontaneous thought flow may start with “lower-order” associative processes supported by MTL memory structures (HPC and PHC) and may continue as information is relayed to “higher-order” evaluative processes supported by default network areas (especially the MPFC) and executive network regions (especially the LPFC). This information about the sequence of neural processes 98  during spontaneous thought could help in the development of models of neural recruitment that more closely reflect spontaneous thought dynamics. Neural contributions to component processes of spontaneous thought The sequence of neural processes during spontaneous thought identified in the present experiments also revealed that different phases of the spontaneous thought process engaged distinct neural systems that make up a larger network of brain regions consistently implicated in spontaneous thought. Compared to previous studies, information collected about when a thought first started in the present experiments allowed the examination of neural recruitment during initial spontaneous thought generation. In addition, information collected about when a thought continued in the present experiments enabled the assessment of neural recruitment during subsequent spontaneous thought elaboration. The pattern of neural recruitment in the present experiments suggests that the MTL (HPC and PHC) may be central to the generation of spontaneous thought, whereas default network regions (especially the MPFC) may be important for the first-pass affective elaboration of or reaction to a spontaneously generated thought. Executive network regions (especially the LPFC) may contribute to further cognitive elaboration or evaluation of a spontaneously generated thought and may monitor and guide the course and content of spontaneous thought flow. Results from the present experiments thus provided empirical support for the theorized contributions of these brain regions to spontaneous thought, which had previously only been inferred indirectly from studies that investigated deliberate mental processes (e.g., memory retrieval, emotion judgment, and complex reasoning). 99  Suppression of generative processes by elaborative processes Findings from Experiment 2 also revealed that spontaneous thought elaboration involves the suppression of neural processes involved in spontaneous thought generation. The examination of neural recruitment during the continuation or linking of spontaneous thoughts revealed correlated activity between the MPFC and MTL only at the beginning of spontaneous thought elaboration. However, the MPFC showed increased activity while the MTL displayed decreased activity during the later stages of spontaneous thought elaboration. These results suggest that spontaneous thought elaboration may involve the suppression of the MTL by the MPFC, providing empirical support for the proposed inhibitory influence of MPFC regions on the retrieval or construction of associations or memories in MTL memory structures. The flow of spontaneous thought may thus depend on the regulation of MTL generative processes by MPFC evaluative regions, leading to the continuation of the current thought content and/or hindering the development of a new stream of thought content. The results from Experiment 2 have important implications for the study and enhancement of creative thinking, which may be facilitated by the minimization of interference between generative processes supported by the MTL and affective evaluative processes supported by the MPFC. Clinical and educational implications In addition to the theoretical and basic neuroscientific implications outlined above, the present findings also bear significance for fields such as clinical neuroscience and education. Spontaneous thought appears to underlie the symptoms of several psychiatric conditions such as depression, but it also helps to promote adaptive cognitive processes such as creativity. Consistent with this, the brain regions and networks implicated in spontaneous thought show 100  disrupted activation in a number of clinical disorders as well as enhanced recruitment during some deliberate, goal-directed mental processes. Balanced interaction between the generative and elaborative neural systems involved in spontaneous thought, as revealed by the present work, may contribute to the treatment of these psychiatric conditions as well as the training of adaptive cognitive processes. Psychiatric disorders The specific characterization of the contributions of various brain regions to spontaneous thought, as revealed in the present experiments, could help improve our understanding of the dysfunctional cognitive processes associated with spontaneous thought, as well as how they could be treated. Several psychiatric conditions are accompanied by disrupted patterns of spontaneous thought, including repetitive, involuntary, negative rumination in depression (Giambra et al., 1994; Nolen-Hoeksema, 2000; Watkins, 2008), recurrent, spontaneous, traumatic memories in PTSD (Berntsen & Rubin, 2008; Ehlers, Hackmann, & Michael, 2004), and excessive distractibility and mind wandering in ADHD (Mooneyham & Schooler, 2013; Smallwood et al., 2007). These conditions also exhibit altered activation in brain areas frequently associated with spontaneous thought (Andrews-Hanna et al., 2014).  Repetitive, spontaneous, and negative cognitions (i.e., rumination) in depression involve self-generated mental events that proliferate or persist because of continuous negative evaluations of the mental events (Grabovac, Lau, & Willett, 2011; Nolen-Hoeksema, Wisco, & Lyubomirsky, 2008; Segal, Williams, & Teasdale, 2002). The excessive, involuntary negative thinking that characterizes depressive rumination may thus reflect aberrant recruitment of brain regions that contribute to the initial affective elaboration of spontaneously generated thoughts 101  (e.g., default network areas, especially the MPFC). It may also reflect decreased recruitment of brain regions that support the cognitive evaluation, monitoring, and control of spontaneous thought flow and content (e.g., executive network areas, especially the LPFC). Mindfulness-based clinical interventions for depression, which train “moment-to-moment, non-judgmental awareness” (Kabat-Zinn, 1990; Segal et al., 2002), may help reduce depressive rumination through promoting a more balanced interaction between brain regions that support the spontaneous affective evaluation of self-generated thoughts (e.g., default network areas, especially the MPFC) and those that contribute to the monitoring and guidance of spontaneous thought flow and content (e.g., executive network areas, especially the LPFC).    Creative thinking A detailed account of the contributions of different brain regions and networks to spontaneous thought, as suggested by the present experiments, could also help increase our understanding of the adaptive cognitive processes associated with spontaneous thought, as well as how they could be enhanced. Spontaneous thought processes have been shown to facilitate several goal-directed cognitive processes, such as memory consolidation and reconsolidation (Ellenbogen et al., 2007; Smallwood et al., 2011), insight and creativity (Baird et al., 2012; Dijksterhuis & Meurs, 2006), and decision making and planning (Dijksterhuis, 2004; Smallwood, Ruby, & Singer, 2013). These cognitive processes have also been associated with activation in brain regions consistently implicated in spontaneous thought (Christoff, 2013).  It has been proposed that creativity involves a twofold process characterized by a generative component facilitating the production of novel ideas or solutions and an evaluative component enabling the assessment of their appropriateness or usefulness (Basadur et al., 1982; 102  Campbell, 1960; Finke et al., 1992; Israeli, 1962). The generation of creative ideas has been associated with the engagement of MTL memory structures, while the evaluation of creative ideas has been associated with the recruitment of both default network regions and executive network areas (Ellamil et al., 2012). However, results from the present experiments suggest that the elaboration of spontaneous thought, which may engage affective evaluation processes in the MPFC, may suppress activation of the MTL, which appears to be central to the generation of spontaneous thought content. Creative thinking may thus be enhanced by engaging in idea generation and idea evaluation separately in order to minimize the interference of elaborative mental processes supported by the MPFC with generative mental processes supported by the MTL. Consistent with this, the practice of brainstorming, which involves the generation of ideas while deferring their evaluation, is known to increase the creativity of outputs (Basadur et al., 1982; Parnes & Meadow, 1959). Thus, switching between associative processes – which may be supported by brain regions linked to the generation of spontaneous thought (e.g., MTL) – and evaluative processes – which may be supported by brain regions linked to the affective elaboration and metacognitive evaluation of spontaneous thought (e.g., MPFC and LPFC) – may promote insight and creativity. Limitations Although the present experiments revealed important information about the sequence and contributions of neural processes during spontaneous thought, it is possible that the results reflect neural recruitment specific to the highly experienced mindfulness meditators recruited as subjects or correspond to the metacognitive awareness required during mindfulness meditation practice. The present experiments recruited mindfulness meditators because observing subtle and 103  transient mental events requires a high level of attention and meta-awareness that meditators have been shown to engage in more successfully than non-meditators (Gruberger et al., 2011). Although this provided a theoretical advantage with respect to the introspective accuracy with which our subjects were able to identify and report on their spontaneous thoughts, it also poses a potential limitation to the present work: it is possible that the pattern of neural recruitment during spontaneous thought identified in the present experiments may not be representative of the population as a whole, due to the unique characteristics of our sample of participants. In addition, the present experiments used mindfulness meditation as the background task to more specifically examine thoughts as they spontaneously arose while keeping the level of metacognitive awareness constant across the different conditions and throughout the experimental sessions. It is possible, however, that the pattern of neural recruitment identified during the present experiments might correspond to the metacognitive awareness involved during mindfulness meditation instead of spontaneous thought processes. While these possibilities cannot be ruled out based on the present work, it should be noted that the pattern of results obtained in the present experiments is highly similar to the activation of default network regions, executive network areas, and MTL memory structures identified in previous studies of spontaneous thought that recruited subjects without extensive mindfulness meditation training (i.e., non-meditators) and used conditions that did not require a high level metacognitive awareness (i.e., rest periods or thought probes during easy tasks) (e.g., Christoff et al., 2009b). In addition, the finding that the MTL may support the spontaneous generation of thought is consistent with a number of previous studies that showed spontaneous neural replay of recent experiences during periods of quiet wakefulness even in the rat MTL (Foster & Wilson, 2006; Sutherland & McNaughton, 2000).  104  Moreover, to examine the extent of these limitations, we specified the number of thoughts reported and hours of meditation experience as covariates of no interest in Experiments 1 and 2. These analyses showed recruitment of the same brain networks and regions during spontaneous thought, suggesting that the pattern of brain activation identified in the present experiments may be independent of meditation experience and likely reflect neural processes that support spontaneous thought. Thus, it is possible that meditation training may result in quantitative changes in brain function (i.e., which areas function and communicate more efficiently), but not necessarily in qualitative changes in the neural mechanisms that support thought (i.e., which structures contribute to the generation and elaboration of thought). However, future research with subjects who do not have introspective training (e.g., non-meditators) could provide further support for and extend the results from these present experiments with subjects that have extensive introspective training. Future directions   Although subjective reports from experienced meditators provided valuable information about the sequence of neural processes during spontaneous thought and their specific contributions to its component processes, a number of questions remain to be answered by future research. It is important for future research to investigate whether a population of participants with little to no meditation training would yield similar results to those from the present experiments. A few studies have shown that mindfulness training and inductions were associated with reduced occurrence of mind wandering (Brewer et al., 2011; Mrazek et al., 2013; Mrazek, Smallwood, & Schooler, 2012), which has been proposed to reflect decreased activation of default network areas as a result of mindfulness meditation (Bærentsen et al., 2010; Brewer et 105  al., 2011). However, it remains to be examined whether greater incidence and chaining of spontaneous thoughts in non-meditator subjects would result in more pronounced default network activation, especially in the MPFC, during similar experience sampling of spontaneous thought as in the present experiments. Some studies have also suggested that the sustained awareness and cognitive control needed for mindfulness meditation are associated with the recruitment of executive network areas (Brefczynski-Lewis et al., 2007; Lazar et al., 2000; Newberg et al., 2001). Again, however, it remains to be examined whether the greater effort that would be required by non-meditator subjects to monitor their thoughts would result in earlier and more constant engagement of the executive network, especially the DLPFC, in the same experience sampling tasks. Such future studies would increase our knowledge of the extent to which meditators and non-meditators differ and are similar in terms of the quantitative (i.e., which brain regions communicate and function more efficiently) versus qualitative (i.e., which brain structures support particular component processes of spontaneous thought) aspects of the neural mechanisms that support spontaneous thought. It would also be beneficial for future research to continue and extend the use of meditator subjects’ introspective or first-person expertise to further study the neural mechanisms of spontaneous thought. Future studies could assess the extent to which neural recruitment during spontaneous thought overlaps with and is modulated by the neural processes that support mind wandering and stimulus-independent thought. First-person reports from meditator subjects with extensive introspective training would allow the examination of the relationship between brain regions and networks that contribute to the process by which a thought occurs (i.e., spontaneously versus deliberately) and those that determine the content of a thought (i.e., its relationship to the current task or sensory information). In addition, the neural mechanisms that 106  correspond to the direction in which a spontaneous thought proceeds (i.e., away from a task or towards a topic of current concern) and the degree of connection between segments of spontaneous thought (i.e., how linked or disparate the thoughts are) remain to be investigated. First-person reports from meditator subjects with great introspective experience could allow the examination of neural recruitment associated with various antecedents and consequents of spontaneous thought segments. Such future studies would enhance our understanding of the interaction between the neural mechanisms that support component processes of spontaneous thought and those that determine the content of spontaneous thought. The present fMRI experiments attempted to strike a balance between sufficient spatial resolution to assess neural recruitment in subcortical regions (e.g., MTL) and adequate temporal resolution to examine the sequence of neural processes during spontaneous thought events. However, the low temporal resolution and inherently correlational nature of fMRI measures make it difficult to draw definitive conclusions regarding the direction of information flow between MTL memory structures, default network regions, and executive network areas as spontaneous thoughts arise and develop. Using modalities with higher temporal resolution than fMRI, such as electroencephalography (EEG) and magnetoencephalography (MEG), may enable a more fine-grained examination of the temporal dynamics of neural recruitment during spontaneous thought, as well as the intermediate neural processes between the initial generation and subsequent elaboration of spontaneous thought (e.g., PCC and TPC recruitment). In addition, real-time fMRI experience sampling procedures using three-way thought probe thresholds (i.e., high activity, low activity, and no activity change), network ROI definitions (e.g., functional connectivity measures or MVPA algorithms), and subject-specified conditions (versus strictly experimenter-determined conditions), as suggested by results from Experiment 3, can provide a 107  more direct test of the causal link between the MTL and spontaneous generation processes, between the MPFC and spontaneous affective elaboration, and the LPFC and higher level, metacognitive evaluation of spontaneous thought. Conclusions The integration of first-person reports from expert mindfulness meditators with third-person neural measures from fMRI experience sampling procedures helped to not only reveal the sequence of neural recruitment during spontaneous thought flow but also to refine current accounts of how brain regions frequently associated with spontaneous thought specifically contribute to its component processes. First-person, introspective information about the timing, sequence, and content of spontaneous thoughts collected in the present experiments indicated that the initial generation and subsequent elaboration of spontaneous thought recruited distinct neural systems, the balanced interaction of which may contribute to recovery from psychiatric conditions such as depression as well as the enhancement of cognitive processes such as creativity. 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Cerebral Cortex, 18, 230-242.  126  APPENDICES Appendix A: Meditation experience questionnaire  T H E  U N I V E R S I T Y  O F  B R I T I S H  C O L U M B I A   xxxxxxxxx xxxxxxxxxxxx xx xxxxxxx xxxxxxxxxx #### – #### xxxx xxxx, xxxxxxxxx, xx, xxxxxx x#x #x# Phone: (###) ### ####   Email: xxxxxxx@xxxxx.xxx.xx  Participant Information  Name  Email  Phone    Demographics  Address (CITY, PROV/STATE, COUNTRY)  Date of Birth (MM/DD/YYYY)  Sex (MALE / FEMALE)  Hand (RIGHT- / LEFT-HANDED)  Vision (NORMAL / GLASSES / CONTACTS)  Occupation & Education (HIGHEST LEVEL/DEGREE)  English (FLUENT / NOT)    Scanner Compatibility  I am claustrophobic. (YES / NO)  I am unable to lie still for extended periods (at least 1 hour). (YES / NO)  I have a psychiatric history. (YES / NO)  I am taking psychiatric medications at the moment. (YES / NO)  I have been a metal worker (grinding, machining, or welding). (YES / NO)    Meditation Experience: MAHASI / VIPASSANA / MINDFULNESS When did you first begin meditating? (MM/YYYY)     127  Retreats (MAHASI / VIPASSANA / MINDFULNESS)  Start Date (MM/YYYY) Length (DAYS/MONTHS) Sitting meditation daily duration Walking meditation daily duration (SPECIFY) Other activities daily duration 1            2            3            4            5             Regular Practice (MAHASI / VIPASSANA  / MINDFULNESS) How many years have you had a regular practice?      Meditation activity  (SITTING, WALKING, etc.) Frequency  (DAYS PER WEEK) Daily duration  (MINUTES/HOURS) 1    2    3    4    5     Other Practices (e.g., ZEN, TM, GOENKA, MANTRA, YOGA, QI GONG, TAI CHI)   Meditation type Frequency  (DAYS PER WEEK) Daily duration  (MINUTES/HOURS) 1    2    3    4    5     128  Appendix B: Task instructions Experiment 1 – Spontaneous thought generation Watch the rising and falling of the stomach or breath throughout the whole task, making sure to keep your eyes open and looking at the screen. Press for the first time with your index finger whenever a thought arises (including in between words) and whenever a word shows up (after reading it). Press for the second time with your: Index finger = if the thought/word was an image Middle finger = if it was a story or verbal Ring finger = if it was about an emotion Pinky finger = if it was about a body sensation 1 star will appear to let you know the first press went through. 2 stars will appear to let you know the second press went through.  Experiment 2 – Spontaneous thought elaboration Watch the rising and falling of the stomach or breath throughout the whole task, making sure to keep your eyes open and looking at the screen. Press with your index finger only when no thought/word comes 1 to 2 seconds after the first thought/word. 1 star will appear to let you know the press went through. Press with your middle finger only when a second thought/word comes 1 to 2 seconds after the first thought/word. 2 stars will appear to let you know the press went through.  Experiment 3 – Real-time fMRI experience sampling Watch the rising and falling of the stomach or breath throughout the whole task, making sure to keep your eyes open and looking at the screen. Whenever the screen flashes white, write down a brief description of your thoughts just before the flash. Draw a line across the bottom of the screen to signal that you are done writing. Draw a line across the blank screen to signal that you do not have any thoughts to report. 129  Appendix C: Word lists Image Narrative Emotion Body Sensation Apple Beach Bed Book Car Cloud Coffee Flower Forest Island Landscape Mountain Newspaper Ocean Pet Phone Picture Rain Sea Smile Ski Sky Snow Sun Tea Trash Tree Umbrella Water Window Home Food Job Work Task Vacation Goals Deadlines Partner Love Family Parents Relatives Friends Interaction Study School Knowledge Mind Self Health Well-being Medicine Illness Death Hobbies Leisure Business Problems Concerns Happy Content Glad Joyful Pleased Calm Sad Unhappy Downcast Glum Upset Angry Mad Annoyed Irate Frustrated Surprised Excited Astonished Startled Afraid Fearful Frightened Worried Anxious Scared Disgusted Shocked Repulsed Ashamed Warmth Heat Hot Cool Cold Heaviness Lightness Numb Vibration Tickle Itch Scratch Pinch Prick Pressure Pain Ache Sore Heartbeat Nerves Knots Tension Stiff Fatigue Tired Hunger Touch Sound Smell Taste  

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