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Neurogenetic variations in norepinephrine availability enhance perceptual vividness Todd, Rebecca M.; Ehlers, Mana R.; Müller, Daniel J.; Robertson, Amanda; Palombo, Daniela J.; Freeman, Natalie; Levine, Brian; Anderson, Adam K. Apr 22, 2015

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Behavioral/CognitiveNeurogenetic Variations in Norepinephrine AvailabilityEnhance Perceptual VividnessRebecca M. Todd,1 XMana R. Ehlers,1Daniel J. Mu¨ller,2 Amanda Robertson,3 XDaniela J. Palombo,3,4Natalie Freeman,2Brian Levine,3,4 and AdamK. Anderson51Department of Psychology, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada, 2Department of Psychiatry, University ofToronto and Neurogenetics Section, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R8, Canada, 3Department of Psychology, Universityof Toronto, Toronto, Ontario, M5S 3G3, Canada, 4Rotman Research Institute, Baycrest Health Sciences, Toronto, Ontario, M6A 2E1, Canada, and5Department of Human Development, Cornell University, Ithaca, New York 1485Emotionally salient aspects of the world are experienced with greater perceptual vividness thanmundane ones; however, such emotion-ally enhanced vividness (EEV) may be experienced to different degrees for different people. We examined whether BOLD activityassociated with a deletion variant of the ADRA2b gene coding for the !2b adrenoceptor modulates EEV in humans. Relative to noncar-riers,ADRA2b deletion carriers showed higher levels of perceptual vividness, with the ventromedial prefrontal cortex (VMPFC) showinggreatermodulation by EEV. Deletion carriers were alsomore sensitive to the featural salience of the images, suggesting amore pervasiverole of norepinephrine inperceptual encoding. Path analysis revealed that,whereas a simplemodel bywhich the amygdalamodulated thelateral occipital complex best characterized EEV-related activity in noncarriers, contributions of an additional VMPFC pathway bestcharacterized deletion carriers. Thus, common norepinephrine-related neurogenetic differences enhance the subjective vividness ofperceptual experience and its emotional enhancement.Key words: ADRA2b; attention; emotion; emotionally enhanced vividness; fMRI; neurogeneticsIntroductionEmotionally salient stimuli typically evoke enhanced attentionand memory compared with more mundane ones (Pourtois etal., 2013). Yet such emotional enhancement of cognition may becharacterized by individual differences that are influenced by ge-notype (Hamann and Canli, 2004). A deletion variant of theADRA2b gene, which codes for the !2b adrenoceptor, is thoughtto be linked to similar effects to those of an !2b receptor antag-onist (de Quervain et al., 2007). ADRA2b has been found to in-fluence emotional enhancement of perception and memory (deQuervain et al., 2007; Rasch et al., 2009; Todd et al., 2013).When salient stimuli are encountered, norepinephrine (NE)release from the locus ceruleus (LC) is associated with alteredperceptual cortical activity (Jones andMoore, 1977; Aston-Jonesand Cohen, 2005; Yu and Dayan, 2005; Donner and Nieuwen-huis, 2013). One potential consequence is altered salience of per-ceptual experience.We recently reported that emotionally salientstimuli are subjectively experienced with greater perceptual viv-idness (Todd et al., 2012), a phenomenon we call emotionallyenhanced vividness (EEV). EEV has been linked to greater acti-vation of object-sensitive regions of visual cortex, an effect medi-ated by amygdala activity (Todd et al., 2012). However, it is notknown whether such interactions are related to NE availability.The goal of the present study was to examine whetherADRA2b genotype influences neural activity linked to EEV. fMRIdata were collected from previously genotyped participants(Todd et al., 2013) while they performed amagnitude estimationtask in which they estimated the relative amount of Gaussiannoise overlaid on emotionally salient and neutral images (Fig. 1;Todd et al., 2012).Higher levels of subjective perceptual vividnessare reflected in ratings of lower relative levels of noise. EEV isobserved when emotionally salient images are rated as more per-ceptually vivid than neutral images.The biased attention by NE (BANE) model (Markovic et al.,2014) stresses the role of NE in affective biases in attention, em-phasizing reciprocal interactions between brain regions that playa key role in valuation networks— specifically the amygdala andventromedial prefrontal cortices (VMPFC; Markovic et al.,2014; Fig. 2). According to this model, the LC/NE can modu-late visual cortex activity both directly and via the amygdalaand VMPFC (for review, see Andrews-Hanna et al., 2010; Pes-soa, 2010; Chikazoe et al., 2014; Markovic et al., 2014). Thus,differences in NE activity may lead to greater activation ofvaluation network nodes and a greater influence of these re-Received Oct. 29, 2014; revised March 13, 2015; accepted March 16, 2015.Author contributions: R.M.T., D.J.M., D.J.P., B.L., and A.K.A. designed research; R.M.T., M.R.E., and A.R. per-formed research; R.M.T., M.R.E., D.J.M., and N.F. analyzed data; R.M.T., M.R.E., and A.K.A. wrote the paper.This researchwas supported by Canadian Institutes for Health Research (CIHR) Operating Grant 491746. D.J.M. isthe recipient of a CIHR Michael Smith New Investigator Salary Prize and an OMHF New Investigator Fellowship. WethankMatthew Dixon for his generous and insightful comments and Sajid Shaikh, David Irwin, and Tayler Eaton fortheir contributions to the research.The authors declare no competing financial interests.Correspondence should be addressed to Rebecca Todd, PhD, Department of Psychology, University of BritishColumbia, 2136 West Mall, Vancouver, BC, V6T 1Z4, Canada. E-mail: becket.todd@psych.ubc.ca.D.J. Palombo’s present address: VA Boston Healthcare System, 150 South Huntington Avenue, Boston,MA 02130.DOI:10.1523/JNEUROSCI.4489-14.2015Copyright©2015 the authors 0270-6474/15/356506-11$15.00/06506 • The Journal of Neuroscience, April 22, 2015 • 35(16):6506–6516gions on visual cortex activity. By combining genotyping withfMRI, we aimed to assess differences in EEV-related blood-oxygenation-level-dependent (BOLD) activation patterns linked tocommon differences in NE activity. We predicted thatADRA2b deletion carriers would show higher levels of EEVthan noncarriers. We further predicted that ADRA2b-relateddifferences in EEV would be associated with greater activationin the amygdala/VMPFC and a stronger pattern of coactiva-Figure 1. Task design for Noise Estimation fMRI experiment. A standard, created by phase scrambling the comparison image, was overlaid with 10%, 15%, or 20% noise. The standard wasfollowed by the target image overlaid with 15% noise. Following image offset, participants moved a cursor on a scale to indicate noise for the image relative to the standard from “a lot less noise”to “same as standard” to “a lot more noise.”Figure 2. Key pathways emphasized by the BANEmodel (Markovic et al., 2014). Green dashed lines indicate norepinephrine (NE) pathways. Red lines indicate projections to the locus coeruleus(LC). Thicker lines indicate direct modulation of visual cortex activity in affect-biased attention. Norepinephrine (NE) activity is implicated in both stimulus encoding and selective attention (Sara,2009). A salient stimulus activates LC neurons, which project widely to cortical and subcortical regions. OFC/VMPFC, Orbitofrontal/ventromedial prefrontal cortex. Reprinted from Behavioral andBrain Research. Copyright (2014), with permission from Elsevier.Todd et al. • ADRA2b Enhances Perceptual Vividness J. Neurosci., April 22, 2015 • 35(16):6506–6516 • 6507tion between these regions and visual cortex activity linked toEEV.Materials andMethodsParticipantsfMRI data were collected from39 healthy, Caucasian young adult humanparticipants (age: 18–35 years, 25 female) with normal or corrected-to-normal vision. These participants had been previously genotyped as partof a related study based at University of Toronto. Participants were ex-cluded if they reported a history of psychiatric disorders, depression, andanxiety. Psychological health was confirmed by scores on the six itemKessler Psychological Distress scale (Kessler et al., 2002). All participantsscores fell above the cutoff score of 14 (Cornelius et al., 2013). Partici-pants were selected for equal numbers of each ADRA2b genotype andgrouped intoADRA2b deletion carriers (homozygous and heterozygous,N! 21) and noncarriers (N! 18) who were matched for sex and work-ing memory performance as measured by a visuospatial working mem-ory task (Todd et al., 2014).Variations in twoother genes have also been associatedwith individualdifferences in affective biases. Carrying a short allele of the 5HTTLPRregion of the serotonin transporter gene has been associated with traitneuroticism (Canli, 2008) and attentional biases and enhanced amygdalaactivation for threatening stimuli (Hariri andWeinberger, 2003;Munafo`et al., 2008). A val158met polymorphism in the COMT gene influencingprefrontal dopamine metabolism is also associated with greateramygdala activation (Smolka et al., 2005) and startle responses to aver-sive stimuli (Montag et al., 2008). Given a high degree of reciprocalactivity between NE, dopaminergic, and serotonergic systems (Sara andBouret, 2012), we also examined these polymorphisms to control fortheir influence on EEV and associated fMRI activation. This allowed usgreater ability to identify the extent to which observed effects areuniquely due to the influence of NE, and allowed us to conduct explor-atory analyses probing effects of these genes on EEV. To the extent pos-sible, ADRA2b deletion carriers and noncarriers were matched forwhether they carried the COMT met and 5HTTLPR short alleles. How-ever, given the limitations of our genotyped participant pool, there weresome inequalities in the distribution of 5HTTLPR genotype betweenADRA2b groups: among participants who did not carry the ADRA2bdeletion variant there were substantially fewer 5HTTLPR long allele car-riers than short allele carriers. In contrast, among ADRA2b deletion car-riers there were equal numbers of participants with and without the5HTTLPR short allele (Table 1).MaterialsTwenty-five negative and 25 positive photos were taken from the Inter-national Affective Picture System (IAPS). Twenty-five neutral photoswere retrieved from the Internet as well as the IAPS. Positive, negative,and neutral images were selected to be equivalent across conditions onbasic low-level image statistics, equated in log luminance (F(2,72) " 1)and RMS contrast (F(2,72) " 1). Positive and negative images were se-lected to be equivalent in ratings of arousal or emotional salience. Basedon ratings by a separate set of participants (Todd et al., 2012), negative,positive, and neutral images did not differ in whether they containedsingle versus multiple objects (F(2,72) " 1, p # 0.1), difficulty of figureground discrimination (scale of 1–7; F(2,72)" 1, p# 0.5), scene complex-ity (scale of 1–7; F(2,72)" 1, p! 0.5), or number of human figures (F(2,72)" 1, p# 0.6).Gaussian all-color noise was superimposed over each image usingAdobe Photoshop 7.0. To minimize variance associated with differencesin luminance and contrast across images, the “standard” image used formagnitude estimation was created tomatch each corresponding “target”image. To create standards that varied as little as possible from pairedimages in featural characteristics, each image was phase scrambled andoverlaid with 10%, 15%, or 20% noise. Both standard and comparisonimages subtended a visual angle of 13$ 9.5°.fMRI proceduresLocalizer task. Our previous research has found that ratings of EEVmod-ulate object-sensitive regions of lateral occipital complex (LOC; Todd etal., 2012). To independently localize category-selective regions of visualcortex, we used a block design task that alternated blocks of line drawingsof objects and scrambled line drawings to localize object-selective regionsof the LOC—an early stage in the ventral object-processing stream (Grill-Spector et al., 1998). The task also included blocks of faces and places tolocalize other category-selective regions of visual cortex. Each 20 s blockcontained five images presented for 4000 ms each. Blocks alternatedrandomly to minimize category predictability with six blocks of eachimage category. In each block participants performed a one-back task.We further used the contrast between object drawings (easy) versusscrambled drawings (difficult) as a measure of working memory loadused to localize frontoparietal regions.Noise estimation task.We used the visual noise magnitude estimation(NsEst) task to (1) elicit subjective ratings of the perceptual vividness ofimages overlaid with Gaussian noise and (2) measure trial-by-trial mod-ulation of BOLD activity by behavioral indices of perceptual vividness. Inthe NsEst task, images and standards were presented in five separate runsof 30 trials. Each image was presented twice at two of three levels ofstandard noise (10, 15, and 20%) for a total of 150 trials (50 negative, 50positive, and 50 neutral). In each 12 s trial (Fig. 1) a standard was pre-sented for 1500ms, followed by a 500ms interstimulus interval, followedby the picture, which was presented for 1500 ms. After a randomly jit-tered interval of 1500ms, 2000ms, or 2500ms, the sliding scale responsemeter appeared for 4000 ms, followed by a randomly jittered intertrialinterval of 2000 ms, 2500 ms, or 3000 ms. Participants used index andmiddle fingers to move a cursor along a 14-point sliding scale to rate thedegree of noisiness of the image relative to the standard. Ratings rangedfrom “A lot less noisy” (1) to “A lot more noisy,” (14) with “The same asstandard” (8) in the center of the scale. Fifty null trials (1/3), consisting of12 s of fixation, were included at randomized intervals. Before enteringthe scanner participants completed a series of 12 practice trials usingneutral stimuli.After data were collected, the following transformations were per-formed on behavioral responses to theNsEst task to serve as indices of (1)perceptual vividness for behavioral data analysis and (2) EEV for fMRIanalysis. First, we mean-centered noise estimation ratings (between 1and 14) and multiplied them by %1 so they reflected the inverse ofnoisiness (NsEst%1)—a positive measure of vividness. This served as ameasure of (1) perceptual vividness for each noise level and emotionalcategory.NsEst%1" (XNsEst# X! NsEst)$ (#1)For item analyses, we calculated a metric of the average perceptual viv-idness for each image used in the task by averaging NsEst%1 for eachimage across all participants in each genotype group. To generate anNsEst%1 regressor that reflected (2) EEV for fMRI analysis, we furtherregressed the objective noise level of the standard (StanNoise; less than,same as, or more than the target) on NsEst%1 for each image used in thetask. The residuals, or residualized NsEst%1 (ResNsEst%1), indexed thevariance in perceptual vividness associated with emotional salience aftercontrolling for accurate identification of objective noise level. This mea-sure of ResNsEst%1 was used as a trial-by-trial parametric modulator inthe fMRI analysis.Oneweek after the scan, participants logged onto awebsite, where theyperformed a surprise recognition memory task (not reported here) andrated each image for emotional salience by rating how “emotionallyarousing” each imagewas. Each of the 75 photoswas randomly presentedwithout noise. Participants were asked to use a numerical scale from 1(the image was not emotionally arousing) to 7 (the image was extremelyemotionally arousing).Table 1. Distribution of COMT and 5HTTLPR genotypes among ADRA2b deletioncarriers and noncarriersADRA2b COMT Val COMT No Val 5HTTLPR Short 5HTTLPR Long TotalDel 14 7 10 11 21No Del 13 5 12 6 18Total 27 12 22 17 39Del, deletion carriers; No Del, deletion noncarriers.6508 • J. Neurosci., April 22, 2015 • 35(16):6506–6516 Todd et al. • ADRA2b Enhances Perceptual VividnessfMRI acquisition. Imaging data were collected with a 3 Tesla Siemensscanner using a 12-channel head coil. Both the localizer and experimen-tal tasks were programmed in E-prime Version 1.2 (Psychology SoftwareTools). Stimuli were presented on a rear-mounted projection screen setat a resolution of 1024$ 758. For each subject, a 3DMPRAGE was usedto acquire a high-resolution T1-weighted structural volume: TR! 1760ms; TE! 2.2 ms; FOV! 256$ 256; slice thickness! 1 mm; 176 slices;total acquisition time! 7:32 min.3D field maps (coplanar with the fMRI slices) were acquired on eachsubject by measuring the phase of non- EPI gradient-echo images at twoecho times (Jezzard and Balaban, 1995; Jenkinson, 2003). Parameters forthe field mapping series were as follows: TR ! 793 ms; TE1 ! 5.19 msand TE2 ! 7.65 ms; flip angle ! 60; FOV ! 211 mm. Thirty-five sliceswere acquiredwith a voxel size of 3.3$ 3.3$ 3.5mm. EPI parameters forthe two functional tasks were as follows: TR! 2000ms; TE! 25ms; flipangle! 78°; FOV! 211 mm.Preprocessing. Functional activation was determined from the BOLDsignal (Friston et al., 1995) using the software Statistical ParametricMap-ping (SPM8; University College London, UK). The first five time pointswere removed from each functional run to allow for BOLD equilibration.After image reconstruction of the time series, slice-timing correction andmotion correction using spatial realignment were performed. We nextapplied the 3D field maps to unwarp the time series, thereby correctingfor EPI image distortions caused by inhomogeneities in the magneticfield and subsequently coregistering individuals’ time series with their T1weighted structural image. The T1 image was bias corrected and seg-mented using template (ICBM) tissue probability maps for gray/whitematter and CSF. Normalization parameters were obtained from thetissue-segmentation procedure and subsequently applied to the time se-ries data (resampling to 3 mm3 voxels). Finally, time series data weresmoothed with a 6 mm full-width half-maximum Gaussian kernel.First-level statistical models. Procedures were identical to those re-ported previously (Todd et al., 2012). For each subject, first-level generallinear models were applied to localizer data and data from the noiseestimation task. Each model included within-session global scaling (de-fault), high-pass filtering to remove low-frequency signal drift (period!128 s), and the AR1 method of estimating temporal autocorrelation.For the localizer data, boxcar stimulus functions were convolved withthe canonical haemodynamic response function (HRF). Condition-specific regressors were included that modeled objects (line drawings)and scrambled objects as well as faces and places.For the experimental data, a delta function regressor was modeled forimage onset and convolvedwith the canonical HRF for each trial. To bestcharacterize our behavioral results, we examined trial-by-trial paramet-ric modulation of BOLD by the full range of our behavioral measure ofEEV across all emotion categories and objective noise levels. Such ananalysis recapitulates the image-by-image item analysis used in the be-havioral data, while allowing comparison with our previous findingsusing this task (Todd et al., 2012). Moreover, ADRA2b may influencesensitivity to low-level perceptual features such as contrast, color, andscene complexity. This design also allowed us to extract contrast files forparametric modulation by EEV after controlling for low-level visual fea-tures. We included five parametric modulators for image onsets, de-scribed by order of entry into themodel as follows: (1) scene complexity,(2) hue, (3) contrast, (4) mean visual saliency, and (5) inverse noiseestimation (NsEst%1). The inverse noise estimation rating (NsEst%1)served as a measure of perceptual vividness. SPM treats the ordering ofregressors such that any shared variance is accounted for by the regres-sors entered first. Thus, this fifth regressor of interest was orthogonalizedwith respect to the featural salience regressors (1–4). Calculation of re-gressors 1–4 for each image was as follows. Objective image statisticswere computed using the Image Processing Toolbox packaged withMATLAB 7.0. Luminance statistics were derived from the average logluminance (Reinhard et al., 2002). Hue was calculated using MATLAB’srgb2hsv function. Edges were detected using a Canny edge detector witha threshold of 0.5. Lines were detected by using a Hough transform andthe number of detected lines was calculated for each image. Visual sa-lience has been defined as those basic visual properties, such as color,intensity, and orientation, that preferentially bias competition for rapid,bottom-up attentional selection (Itti and Koch, 2001). While visual sa-lience has been used to predict sequential attentional selection of regionswithin a single image, we derived a measure of mean global saliency foreach image to control for visual salience differences between images. Toderive image-specific salience magnitudes, visual saliency was computedby averaging the saliency values across all image pixels using the SaliencyToolbox (Walther and Koch, 2006).ResNsEst%1 regressor. Our goal was to compare differences in BOLDresponse reflecting EEV in each group. As reported below, behavioraldata in noncarriers at the group level did not show statistically significantdifferences between arousing and neutral stimuli, they showed the samedirection of response as deletion carriers. Because there was a similartrend in the noncarriers, we expected to be able to pick up on neuraldifferences in noncarriers between the two conditions. Thus, to generatea ResNsEst%1 regressor, after averaging NsEst%1 across participants im-age by image, we calculated standardized residual NsEst%1 values aftercontrolling for the objective noise level of the standard. We did this forADRA2b deletion carriers and noncarriers separately to probe brain ac-tivation specifically associated with the aspect of perceptual vividnesslinked to emotional salience. The standardized residuals thus served as anindex of EEV that could be examined trial by trial across the task. Becausethis regressor was entered into the regression last, variance shared withlow-level features was partialed out and ResNsEst%1 accounted for onlythe unique remaining variance. This approach also allowed us to furtherexamine regions modulated by low-level features.Second-level statistical models. Regions of interest for key regions spec-ified by previous research and by the BANE model were defined usingfunctional and anatomical templates. The functional localizer task wasused to define visual cortex regions expected to be modulated by EEV aswell as frontoparietal regions implicated in executive attention. For thelocalizer task,T contrast files for each condition (object drawings, scram-bled objects, and places and faces) fromeach individualwere entered intoa one-way ANOVA, with condition as the single factor. The contrast for[objects# scrambled objects] was used to specify shape-selective activa-tion in the LOC. Functionally defined masks were created using 10 mmspheres around maxima activations in the group maps (MNI coordi-nates: 51, %76, 1 and %45, %79, 1) thresholded at p " 0.05 (FWE).Similarly, activation in parietal regions associated with the one-back taskyielded the center coordinates for the corresponding masks (%33,%55,49 and 36,%55, 43) also with a threshold of p" 0.05 (FWE). Anatomicalmasks for right and left amygdala and VMPFC were created from auto-mated anatomical labeling (AAL) templates (Tzourio-Mazoyer et al.,2002) based on a spatially normalized high-resolution T1 single-subjectdataset using theMarsBaR toolbox (Brett et al., 2002). AAL templates forleft rectal gyrus andmedial orbitofrontal cortex (OFC)were combined tocreate the VMPFC mask. Together, these ROIs were used for small vol-ume correction for the noise estimation task.For the noise-estimation task our primary goal was to examine therelationship between ADRA2b genotype and BOLD activation modu-lated by EEV. A two-sample t test based on the contrast files for ResNs-Est%1 from the first-level parametric analysis was performed to directlycompare ADRA2b deletion carriers and noncarriers. Although our pri-mary focus was on ADRA2b, because of group differences in the ratio of5HTTLPR short allele carriers to noncarriers, we wanted to statisticallycontrol for the potential influence of 5HTTLPR on our results. Second-arily, we also wanted to examine potential main effects and interactionswithADRA2b. Thus, 5HTTLPRwas included as a covariate in the group-level analysis. As the distribution of COMT genotype was equal acrossADRA2b groups, and preliminary analyses revealed no effects of COMT,COMT was not included in this analysis. Results of the omnibus test forthis analysis, thresholded at p " 0.05 after controlling for FWE, arereported in Table 2.Path analysis.To further probe results of our voxelwise examination ofEEV-related activation, we next used path analysis to examine potentialcoactivation patterns between regions associated with trial-by-trial sub-jective ratings of EEV. This approach was optimal for examining resultsof our parametric modulation because, unlike other approaches tomod-eling coactivation patterns (e.g., dynamic causal modeling), it did notrequire a full factorial design. To extract time series information for theTodd et al. • ADRA2b Enhances Perceptual Vividness J. Neurosci., April 22, 2015 • 35(16):6506–6516 • 6509path analysis, a separate first-level analysis including six regressors foremotion category (positive, negative, and neutral) and noise level (10, 15,and 20% noise) was performed. The delta function regressors were usedto model stimulus onset for emotion category and standard noise level.Unadjusted signal was extracted from the first eigenvariate of a 3 mmradius spherical volume of interest (VOI). The VOI was centered on thecoordinates of the local maximum within an anatomically bounded re-gion defined by AAL templates for left amygdala and VMPFC, respec-tively. Peak activation in these regions was based on the first-levelcontrast [emotionally arousing# neutral]. For the functional ROI “leftLOC,” the sphere was centered on the coordinates of the local maximum(%51,%67, 16) resulting from the second-level analysis of the functionallocalizer. To obtain comparable time series data, ResNsEst%1 was con-volved with the hemodynamic response function. Both ROI time seriesdata and ResNsEst%1 ratings were averaged separately for the twoADRA2b variants at each time point. We thus obtained time point bytime point ResNsEst%1). The SPSS add-on module AMOS (IBM SPSSAmos, Version 21.0) was used to confirm the results and to obtain dif-ferent indices for model fit.Model fit can be assessed by various fit indices. The parsimonygoodness-of-fit index (PGFI) calculates the proportion of variance ac-counted for by the estimated population covariance; hence, better modelfit is indicated by larger values (Mulaik et al., 1989). The standardizedroot mean square residual (SRMR), with values smaller than 0.05 indi-cating good fit (Byrne, 1998), is based on the square root of the differencebetween the residuals of the sample covariance matrix and the hypothe-sized covariance model (Hooper et al., 2008). The corrected Akaike in-formation criterion (AICc) is a relative goodness-of-fit index consideringmodel complexity and allowing direct comparison of models. SmallerAICc values are an indicator for a better fit (Akaike, 1974). Finally, themost commonly used index is % 2, which relies on the difference betweensample andmodel covariance matrix (Hu and Bentler, 1999). A small % 2and a p value bigger than 0.05 suggest a good fit of the model (Barrett,2007). We report all of these values in the results of the model compari-son below.GenotypingGenotyping was performed by the Neurogenetics Laboratory at the Cen-tre for Addiction and Mental Health in Toronto, Canada. For this pur-pose, a 2 ml sample of saliva had been collected from each participantusing an Oragene OG-500 DNA kit (DNA Genotek). DNA was ex-tracted as per manufacturer’s instructions and diluted to 20 ng/&lworking concentration.For the ADRA2b 9 bp deletion locus, total genomic DNA (60 ng) wascombined with 1$MBI Fermentas PCR buffer containing KCl, 1.5 mMMgCl2 (MBI Fermentas), 0.0325 &g of each primer (forward primersequence: 5& HEX-CAGAAGGAGGGTGTTTGTGG; reverse primer se-quence: 5& CCACTGCCCACCTATAGCAC), 0.2 mM each dNTP (MBIFermentas), and 0.6 U Taq polymerase (MBI Fermentas) to a total vol-ume of 15&l in a 96-well PCRplate. The PCRswere subjected to an initialdenaturation for 5 min at 95°C, followed by 30 cycles of amplification inan AB 2720 thermal cycler: denaturing for 30 s at 95°C, annealing for 30 sat 60°C and extension for 30 s at 72°C, and a final extension at 72°C for 10min. Similarly for the SLC6A4 LPR (5HTTLPR), 40 ng total genomicDNA was combined with 1$ MBI Fermentas PCR buffer containing(NH4)2SO4, 1.5 mM MgCl2 (MBI Fermentas), 0.0325 &g of each primer(forward primer labeled with 5& HEX fluorescent tag), 0.16 mM eachdNTP (MBI Fermentas), and 1 U Taq polymerase (MBI Fermentas) to atotal volume of 25&l in a 96-well PCR plate. The PCRs were subjected toan initial denaturation for 3 min at 95°C, followed by 40 cycles of ampli-fication in an Eppendorf Mastercycler Pro S thermal cycler: denaturingfor 30 s at 95°C, annealing for 30 s at 61°C and extension for 1 min at71°C, and a final extension at 72°C for 10min. Fivemicroliters of the PCRproduct was combined with 1$New England BioLabs Buffer 2 and 10 UMspI restriction enzyme (New England BioLabs) in a total volume of 30&l was digested overnight at 37°C. For both ADRA2b and the LPR, thefinal products were electrophoresed on an AB 3130-Avant Genetic Ana-lyzer as per manufacturer’s directions, and product sizes determined bycomparison to GeneScan 500 ROX size standard using GeneMapper(version 4.0).For COMT, an SNP was genotyped using TaqMan predesigned assays(Life Technologies): Val158Met in the COMT gene (rs4680; assay IDC_25746809_50). Twenty nanograms of genomic DNA were amplifiedas permanufacturer’s directions scaled to a total volumeof 10&l in anAB2720 thermal cycler. Postamplification products were analyzed on theABI Prism 7500 Sequence Detection System using the allelic discrimina-tion option, and genotype calls were determined manually by compari-son to six No Template Controls.Genotyping of 10% of samples from each run was replicated for qual-ity control purposed for each marker.ResultsFor all analyses, based on previous research (de Quervain et al.,2007; Rasch et al., 2009), homozygote and heterozygote ADRA2bdeletion carriers were treated as a single group due to the lownumber of homozygotes. Similarly, homozygous and heterozy-gous carriers of the 5HTTLPR short allele (Canli and Lesch, 2007)and the COMT val allele were also treated as a single group.Twenty-two participants carried the 5HTTLPR short allele and17were homozygous long allele carriers; 27 carried theCOMT valallele and 12 were homozygous met carriers.Behavioral resultsNoise estimation taskBecause our focuswas on EEV as our dependentmeasure, we firstcalculated NsEst%1 as a measure of perceptual vividness in eachcondition. Thus NsEst%1 served as an index of the vividness ofthe signal of the underlying image in relation to the overlaidnoise. To examine genotype-related differences in NsEst%1 re-lated to the emotional salience of the stimulus and the objectivelevel of standard noise, we performed a three-way repeated-measuresANOVAwith emotion category (negative, positive, andneutral) and standard noise level (10, 15, and 20%) as within-subject factors. Genotype groups (ADRA2b, 5HTTLPR, andCOMT) were between-subject factors. All results were Green-house–Geisser corrected for violations of sphericity when neces-sary and contrasts were Bonferroni corrected for multiplecomparisons.Within-subject effectsResults revealed a main effect of noise level (F(2,66)! 76.05, p"0.001, 'p2! 0.70). Linear contrasts revealed that participants ac-curately rated the comparison pictures as less noisy relative to theTable 2. fMRI omnibus test resultsBrain region BA x y z Voxelsa F z pLeft middle occipital gyrus 19 %48 %79 4 81 20.28 5.61 0.001Right inferior occipital gyrus 19 45 %76 %5 52 19.17 5.49 0.001Right Fusiform/parahippocampal gyrus 30 30 %40 %8 450 18.55 5.43 0.001Left middle orbitofrontal/rectal gyrus 11 %12 32 %11 52 17.62 5.32 0.003Left fusiform gyrus 37 %30 %49 %8 245 15.52 5.04 0.011aCluster size at p" 0.001 uncorrected. Regions parametrically modulated by emotionally enhanced vividness (EEV) by genotype after controlling for objective salience; x, y, z, coordinates are in MNI space. P values are FWE corrected formultiple comparisons.6510 • J. Neurosci., April 22, 2015 • 35(16):6506–6516 Todd et al. • ADRA2b Enhances Perceptual Vividnessstandards with increasing standard noise levels (F(1,33) ! 82.12,p " 0.001). Thus, participants were reliably sensitive to differ-ences in levels of objective noise. There was also a main effect ofemotion category (F(2,66)! 21.36, p" 0.001, 'p2! 0.39). Despitecontaining identical levels of noise, contrasts showed that bothpositive and negative images were perceived asmore perceptuallyvivid relative to the standards than neutral images (F(1,33) !39.89, p " 0.001). Negative and positive pictures were rated asmore vivid than neutral pictures at all noise levels (ps " 0.05).Vividness ratings for positive and negative images did not differfrom each other at any noise level (ps# 0.9). There was also aninteraction between noise and emotion category (F(4,132)! 3.67,p! 0.007,'p2! 0.10), showing themain effects reported above tobe greatest at the lowest level of standard noise and reducing withstandard noise level. Whereas vividness ratings for both positiveand negative images were higher than for neutral images at noiselevels 1 and 2, at noise level 3 only negative images were rated asmore vivid than neutral (ps " 0.05). Thus, although noise esti-mation was overall accurate, there was a pronounced effect ofEEV, with participants rating emotionally salient images as lessnoisy, or more perceptually vivid, than neutral images. This ef-fect, which replicates previous findings (Todd et al., 2012), wasmore pronounced at lower levels of standard noise.Between-subject effectsTherewas amain effect ofADRA2b (F(1,33)! 4.51, p! 0.04,'p2!0.12), showing that deletion carriers rated all images as noisier, oroverall lower in vividness than noncarriers. Crucially, the maineffect of ADRA2b was qualified by an interaction with emotioncategory (F(2,66) ! 6.49, p ! 0.003, 'p2 ! 0.16; Fig. 3a), withdeletion carriers showing more of an effect of EEV than noncar-riers. That is, deletion carriers indicated higher levels of percep-tual vividness for negative and positive relative to neutral imagesthan noncarriers, and contrasts between emotionally salient andneutral images were significant in deletion carriers (ps " 0.05)but not noncarriers (ps# 0.2). Aside from ADRA2b, there wereno significant main effects of genotype, and there were no inter-actions with emotional category or noise level (ps# 0.15) relatedto COMT or 5HTTLPR genotype (ps # 0.18). In summary, aspredicted, deletion carriers showed greater effects of emotioncategory on noise estimation ratings than noncarriers, indicatinghigher levels of EEV. Thus, the extent to which emotionally sa-lient relative to neutral pictures are experienced as more percep-tually vivid differs across individuals and is dependent on geneticvariation linked to NE.Arousal ratingsArousal ratings were missing from two participants who failed tolog on 1 week later (one deletion carrier and one noncarrier). Athree-way repeated-measures ANOVAwas performed on arousalratings with emotion category (negative, positive, and neutral)as the within-subject factor and genotype group (ADRA2b,5HTTLPR, and COMT) as between-subject factor. Resultsshowed a main effect of emotion category (F(2,60)! 126.63, p"0.001, 'p2 ! 0.81). Ratings for each emotion category differedfrom each of the others, with highest arousal ratings for negativeimages (mean! 4.72), next highest for positive images (mean!4.02), and lowest for neutral images (mean! 1.55; ps" 0.005).There were no main effects of genotype or interactions betweengenotype and emotion (ps # 0.24). Thus while arousal ratingsreflected normalized ratings of the stimulus categories, subjectiveratings of arousal did not differ by genotype group.Figure3. The influence ofADRA2b onbehavioral andneuralmeasures of emotionally enhanced vividness (EEV).a, Difference scores for ratings of inverse noise estimation (NsEst%1) for negativeand positive# neutral stimuli in noncarriers and carriers of theADRA2b deletion variant. Deletion carriers showgreater EEV than noncarriers.b, Statisticalmaps showing parametricmodulation byEEV in the ventromedial prefrontal cortex (VMPFC) for ADRA2b carriers# noncarriers, and in the lateral occipital complex (LOC) showing modulation by EEV across both groups (n! 37). c, d,Illustration of trial-by-trialmodulation of VMPFC (c) and left LOC (LLOC;d) by EEV over the time course of the hemodynamic response forADRA2bdeletion carriers (n! 21) andnoncarriers (n! 18).The trial axes are rank ordered (from right to left) from highest (1) to lowest (150) ratings of EEV.Todd et al. • ADRA2b Enhances Perceptual Vividness J. Neurosci., April 22, 2015 • 35(16):6506–6516 • 6511Item analysesIn a further step, we performed an item analysis to ascertainthe influence of emotional salience on perceptual vividness, im-age by image, in each group separately. For this analysis eachmeasure of interest, including measures of emotional salience,noise estimation, and measures of the low-level features of eachimage, was averaged across participants for each image used inthe experiment. To obtain our emotional salience measure, wecalculated the mean emotional arousal ratings for each imagefrom each participant and then averaged this value across partic-ipants for each image. To obtain a measure indexing perceptualvividness we calculated NsEst%1 (i.e., the inverse of the mean-centered noise estimation). As measures of featural salience, weobtained the metrics for each image, including number of edges,hue, and a global computationalmetric of visual salience (Itti andKoch, 2001). Separate correlation analyses in ADRA2b carriersand noncarriers revealed that, image by image, mean arousalratings and NsEst%1 were significantly correlated in deletion car-riers (r! 0.34, p! 0.003). The correlation between arousal andNsEst%1 was positive, but nonsignificant in noncarriers (r !0.18, p! 0.13). There was a significant correlation between Ns-Est%1 and visual salience for deletion carriers (r! 0.26, p! 0.01)and for noncarriers (r! 0.34, p! 0.001), indicating that withineach group, greater perceptual vividness was also influenced bylow-level featural salience. In a next step, hierarchical multipleregressions were performed for each group. Measures of featuralsalience (hue, scene complexity, and visual salience) were enteredat the first level. Arousal ratings (emotional salience) were en-tered at the second level. Results revealed that, after controllingfor low-level features, emotional salience predicted NsEst%1 indeletion carriers (R2'! 0.05, p! 0.04). Emotional salience didnot significantly predictNsEst%1 in noncarriers (R2'! 0.01, p!0.39). In contrast, featural salience contributed to perceptual viv-idness for both deletion carriers (R2' ! 0.11, p ! 0.04) andnoncarriers (R2' ! 0.14, p ! 0.02). Thus, item analyses per-formed for each group separately revealed that featural saliencehad similar effects on perceptual vividness in both ADRA2b car-riers and noncarriers. In contrast, only deletion carriers demon-strated a reliable influence of emotional salience on perceptualvividness.Although examination of the effects ofADRA2b on emotionalenhancement of memory (EEM) was not the focus of the presentstudy, for continuity with previous research we did examine theinfluence of ADRA2b on EEM. Analysis of memory vividnessratings and recognition memory accuracy revealed no influenceofADRA2b on overall memory or the effect of emotion onmem-ory (ps# 0.60).fMRI resultsUnless otherwise specified, all results are reported with FWE cor-rection for multiple comparisons either at the whole-brain levelor with small-volume correctionwithin prespecifiedmasks. All x,y, z coordinates are in MNI space.Omnibus effects of genotype on modulation by EEVContrast files for ResNsEst%1, indexing the trial-by-trial modu-lation of BOLD activity by EEV, after controlling for the contri-bution of low-level features of each image, were entered into atwo-sample t test with ADRA2b deletion carriers and noncarriersas independent groups. The 5HTTLPR genotype was included asa covariate. Regions significantly activated within this model at athreshold of p " 0.001, corrected for FWE, are summarized inTable 2. Specific contrasts characterizing activation at each locusare discussed below.Effects of ADRA2b genotype on modulation by EEVContrasts revealed that for both ADRA2b carriers and noncarri-ers, activation in the left LOC [(%48,%73, 7); t! 5.69, z! 4.76,FWE p " 0.001 svc], was modulated by ResNsEst%1. The samepattern was observed in right LOC [(54, %70, 7); t ! 3.86, z !3.50, FWE p ! 0.02 svc]. Thus, after controlling for featural sa-lience and 5HTTLPR allele, greater ratings of EEV were reflectedin greater LOC activation in both groups (Fig. 3b). This resultreplicates our previous finding of enhanced LOC activity withhigher levels of ResNsEst%1, suggesting that the subjective expe-rience of perceptual vividness, or enhanced seeing, is linked togreater activation in object-sensitive regions of the visual cortex.Importantly, it further indicates that this aspect of EEV is simi-larly mediated by visual cortex activity in both ADRA2b deletioncarriers and noncarriers alike. To a lesser degree, EEV modula-tion in our a priori-defined left amygdalar region was also ob-served across all participants [(%24,%1,%23); t! 1.98, z! 1.92,p ! 0.03 uncorrected], although contrasts revealed that activa-tion in the left amygdala was greater for deletion carriers thannoncarriers [(%27, %1, %23); t ! 2.01, z ! 1.95, p ! 0.03 un-corrected].In contrast, activity in the VMPFC unambiguously differenti-ated ADRA2b deletion carriers from noncarriers (Fig. 3b,d): De-letion carriers showed greater positive modulation by EEV thannoncarriers in the left VMPFC,with a peak activation in the rectalgyrus [(%12, 29, %14); t ! 3.84, z ! 3.48, FWE p ! 0.048 svc].Thus, emotional enhancement of vividness was associated withgreater VMPFC signal in deletion carriers versus noncarriers.Activation in the right intraparietal sulcus (IPS) (33,%58, 46) acti-vated by the attention localizer showed the opposite pattern: activa-tionwasnegatively associatedwithResNsEst%1 for deletion carriersbut not for noncarriers (t! 3.81, z! 3.46, FWE p! 0.02 svc). Indeletion carriers, activity in the IPS, associated with executiveattention, decreased when EEV increased. In summary, theADRA2b polymorphism-differentiated brain activity correlatedwith EEV in two regions.Deletion carriers showed greater activityin the VMPFC, a key BANE node implicated in salience evalua-tion, relative to noncarriers. At the same time, deletion carriersalso showed negatively correlated activation in a parietal regionmediating executive attention, suggesting fewer executive re-sources were recruited in trials that were higher in EEV.As tonic noradrenergic activity is sensitive to salience in gen-eral (Aston-Jones and Cohen, 2005), including low-level visualsalience, we performed a follow-up analysis on activity modu-lated by the regressor for image contrast included in the samefirst-level model. We investigated image contrast because it is afeature we have previously found to evoke activity in theamygdala and visual cortices. Results showed that VMPFC activ-ity was more sensitive to contrast in deletion carriers than non-carriers [(0, 41, %20); t ! 3.79, z ! 3.46, FWE p ! 0.03 svc],indicating an influence of ADRA2b on sensitivity to low-levelvisual salience in this region as well. It should be noted, however,that the VMPFC modulation by EEV we reported was based onfirst-level contrasts in which variance due to low-level featureswas partialed out. Thus these contrasts reflected variance that wasunique to EEV.Control analysis: effects of 5HTTLPR genotype on modulationby EEVHere we further examined contrasts indexing effects of the cova-riate modeling 5HTTLPR genotype, focusing on regions wheremodulation by ResNsEst%1 was greater for short allele carriers, aswell as contrasts modeling interactions between 5HTTLPR and6512 • J. Neurosci., April 22, 2015 • 35(16):6506–6516 Todd et al. • ADRA2b Enhances Perceptual VividnessADRA2b. Modulation by ResNsEst%1 was greater for short allelecarriers in the left VMPFC [(%12, 32, %14); t ! 6.12, z ! 5.01,FWE p " 0.001 svc], as well as in the right amygdala [(33, %7,%14); t! 3.59, z! 3.29, FWE p! 0.02 svc]. Thus, carrying theshort allele of 5HTTLPRwas linked to enhancedEEVmodulationin the same region of left VMPFC as carrying the ADRA2b dele-tion variant; however, in short allele carriers amygdala modula-tion by EEV was in the right hemisphere. It should be noted thatthe results we report for ADRA2b are significant after accountingfor the variance due to 5HTTLPR.InteractionsAlthough our sample size was too small to reliably test gene $gene interactions, exploratory examination of potential interac-tions revealed a cluster in the left VMPFC [(%12, 32, %14); t !5.95, z! 4.91, FWE p" 0.001 svc]. This cluster showed a patternof interaction between ADRA2b and 5HTTLPR genotype, suchthat there was greater modulation by EEV for noncarriers of theADRA2b deletion variant that carried the short 5HTTLPR allelethan deletion carriers who carried the short 5HTTLPR allele.Path analysisThe models selected for path analysis focused on statistical influ-ences among regions that have been implicated in EEV and areindicated by the BANE model, which emphasizes reciprocal in-teractions between the LC/NE system andthe amygdala, VMPFC, and visual corticesin enhancing attention to affectively sa-lient stimuli (Markovic et al., 2014). Theamygdala is a key target site for the NEsystem and is rich in NE receptors (JonesandMoore, 1977). Indirectmodulation ofvisual cortex activity by NE can be ob-served via LC modulation of VMPFC andamygdala activity, which in turn influ-ences visual cortex activity (Waterhouseet al., 1990; Gallagher and Holland, 1994;Roozendaal et al., 2009). Finally, the me-diating role of the amygdala and the con-tribution of the left LOC to EEVhave beendemonstrated previously (Todd et al.,2012), and the results of the parametricmodulation further revealed differentialVMPFC activation by ADRA2b genotype.We thus focused on two competingpath-analysis models to specify how be-havioral ratings of EEVmay be influencedby the contribution of VMPFC to previ-ouslymodeled LOCand amygdala activityin carriers and noncarriers of theADRA2bdeletion variant: a parsimoniousmodel inwhich the influence of the left LOC onEEV is directly modulated by the leftamygdala, and a secondmodel which is anextension of the simple model that adds adirect path fromVMPFC to EEV. Becauseof limitations in imaging the human LC(Astafiev et al., 2010), we did not includethe LC in either model.The parsimonious model (Fig. 4a) re-vealed a fit for both deletion carriers(%2(2)! 1.08, p! 0.60, SRMR! 0.0159,PGFI! 0.166, AICc! 36.62) andnoncar-riers (%2(2) ! 0.301, p ! 0.58, SRMR !0.0092, PGFI ! 0.167, AICc ! 35.85). As the overall model fitsuggests, activation of the left amygdala predicted left LOCactivity (deletion: b ! 0.6, p " 0.001; no deletion: b ! 0.318,p" 0.001), which in turn predicted EEV (deletion: b! 0.051,p ! 0.023; no deletion: b ! 0.05, p ! 0.039) for both geno-types. This suggests that the amygdala plays a key role in theemotional modulation of perceptual vividness regardless ofNE-related genotypic variation.The second model (Fig. 4b) models the high level of covari-ance between amygdala and VMPFC activity (r ! 0.46, p "0.001). This dual-route model did not predict EEV adequately innoncarriers (%2(1)! 10.63, p! 0.005, SRMR! 0.041, PGFI!0.198, AICc! 67.50). In contrast, the time series data of deletioncarriers fit the model well (%2(1) ! 5.64, p ! 0.06, SRMR !0.026, PGFI! 0.199, AICc! 62.52). The model implicates that,in deletion carriers, the amygdala (b! 0.51, p" 0.001) mediatesthe influence of left LOC on EEV (b ! 0.033, p ! 0.148); how-ever, in addition, VMPFCdirectly influences EEV (b! 0.047, p!0.018), evenwhen left amygdala and LOC serve as covariates (b!0.019, p" 0.001). In thismodel this pathway accounted formoreof the variance in EEV than the amygdala/LOC pathway. Thus,the two-path model best describes the contribution of brain re-gions to EEV in deletion carriers.Figure 4. a, Parsimonious model predicting emotionally enhanced vividness (EEV) in noncarriers (n! 18) of the ADRA2bpolymorphism by left lateral occipital complex (LLOC) activitymediated by the left amygdala (LAM). b, Complexmodel predictingEEV in deletion carriers (n! 21) of the ADRA2b polymorphism. The dual-route model demonstrates that the left amygdalamediates the effect of LLOC on EEV and simultaneously ventromedial prefrontal cortex (VMPFC) contributes to EEV. For bothmodels,(-estimates for each path are shown. Significant paths are indicated by solid lines, dashed lines indicate nonsignificance.Bidirectional arrows between left amygdala and VMPFC indicate covariance of these regions, which exhibited a high level ofcorrelated activity (r! 0.46, p" 0.001), and the covariance statistic indicating the relation between the two variables is shown.Todd et al. • ADRA2b Enhances Perceptual Vividness J. Neurosci., April 22, 2015 • 35(16):6506–6516 • 6513Amygdala response to arousalFinally, to link the present findings to previous studies, we usedthe factorial model reported above to examine differences inamygdala activation in ADRA2b carriers relative to noncarriersfor negative relative to neutral images. Contrast files for nega-tive # neutral trials revealed activation in the left amygdala[(%15, %4, %17); t ! 1.89, z ! 1.85, p ! 0.03 uncorrected],showing a similar pattern to those previously reported (Rasch etal., 2009) but only at an uncorrected threshold. Differences in thesize of the effect may reflect lower power due to the smaller sam-ple size used in this study. Differences in the extent of the effectmay also be due to differences in the experimental task (our taskrequired cognitive distraction fromaffective content, whereas thestudy by Rasch et al., 2009 required explicit focus on valence andarousal).DiscussionBehavioral results showed that, as predicted, carriers of theADRA2b deletion variant showed higher levels of subjectivelyexperienced perceptual vividness for emotionally salient images(EEV) than noncarriers. Deletion carriers perceived decreasedmagnitude of Gaussian noise embedded in emotionally arousingimages, indicating more vivid perceptual experience of the un-derlying image, and demonstrated greater coupling between re-ported emotional arousal and perceptual vividness.ADRA2b deletion carriers have been found to have greateremotional enhancement of memory and susceptibility to intru-sive memories following trauma (de Quervain et al., 2007), aswell as higher levels of amygdala activation at encoding (Rasch etal., 2009; Cousijn et al., 2010). Our previous research has foundthat deletion carriers show enhanced attentional tuning to emo-tionally salient stimuli (Todd et al., 2013), and a stronger linkbetween perceived arousal of stimuli at encoding and subsequentmemory (Todd et al., 2014). In the present study ADRA2b dele-tion carriers showed greater effects of EEV than noncarriers.These behavioral findings suggest that naturally occurring differ-ences in NE receptor function underlie individual differences inthe vividness with which we perceive emotionally relevant fea-tures of the environment.fMRI results revealed that both deletion carriers and noncar-riers showed modulation of LOC activation by EEV, suggestingthat for both groups the experience of enhanced perceptual viv-idness is linked to enhanced activation in regions of visual cortexassociatedwith object perception and extraction of semantic con-tent (Todd et al., 2012). In contrast, in the VMPFC, greater EEV-related activationwas found in deletion carriers than noncarriers.The finding that greater VMPFC activation modulates EEV forADRA2b deletion carriers is consistent with the proposal that, inhumans, NE plays a role inmodulating affective biases in percep-tual encoding via activation in important nodes of the BANEnetwork (Markovic et al., 2014). The findings of strong groupdifferences in activation in VMPFC support the hypothesis thatenhanced EEV is supported by a partially distinct mechanism innoncarriers.Anatomical data indicate that theVMPFC is closely connectedto regions associated with internally generated states rather thanthose appraising features of the external world (Andrews-Hannaet al., 2010). VMPFC is also linked to regions sensitive to ap-praisal of stimuli such as the amygdala and more lateral OFC(Carmichael and Price, 1996; Price et al., 1996; Rempel-ClowerandBarbas, 1998; Barbas et al., 1999; Cavada et al., 2000; Croxsonet al., 2005). A recent study using multivoxel pattern analysis(MVPA) in humans reported population activity in VMPFC thatwas sensitive to both positive and negative stimuli and indepen-dent of stimulus modality, reflecting a more subjective quality ofaffect (Chikazoe et al., 2014). These data suggest that, whereas theamygdala plays a role in appraising the salience of features of theexternal world, the VMPFC is more involved in aspects of emo-tional evaluation and experience that are internally generated.Deletion carriers also showed greater EEV-related decreases inIPS, a key region in frontoparietal control networks, than in non-carriers. IPS activity specifically modulates executive aspects ofworking memory (Rottschy et al., 2012; Nee et al., 2013) andincreases with attention to visual detail (Guerin et al., 2012). Wepreviously found this region to be negatively associatedwith EEV,suggesting increased task-related visual attention to images expe-rienced as less perceptually vivid, and indicating a trade-off be-tween attentional executive and affective salience networks(Todd et al., 2012). The present findings suggest that this trade-off can be observed in ADRA2b deletion carriers only, suggestingthat individual differences related to NE receptor activity play arole in this interaction between perceptual and attentionalsystems.The BANEmodel (Markovic et al., 2014) emphasizes the roleof NE in tuning valuation systems mediating enhanced encodingof emotionally salient aspects of the world. A salient stimulusactivates LC neurons, which project widely to cortical and sub-cortical regions (Sara, 2009; Sara and Bouret, 2012). In additionto directly altering the gating and tuning of neuronal activity inthe visual cortex, the LC modulates visual cortex activity indi-rectly via the amygdala and prefrontal cortices (Waterhouse et al.,1990; Gallagher and Holland, 1994; Roozendaal et al., 2009). De-scending influences from both the amygdala and OFC/VMPFCprovide information about contextually determined relevance(Aston-Jones and Cohen, 2005), which can then modulate thepattern of LC firing to reflect salience within the given context(Fig. 2).The goal of our path analysis was to elaborate on the trial-by-trial modulation of the BOLD response by subjective ratings ofEEV that reflected our behavioral findings. This analysis sup-ported a model in which deletion carriers recruit additionalnodes of valuation networks emphasized in the BANE model. Itsuggests that, for noncarriers, a simplemodel by which amygdalaactivation modulates the influence of visual cortex activation onEEV explains the data better than a more complex model thatincludes the VMPFC. Thus, for noncarriers, tagging of stimulussalience by the amygdala may heighten activity in the LOC that isdirectly related to processing of the visual stimulus. This in turnresults in the heightened experience of perceptual vividness. Incontrast, for deletion carriers the data were better explained by amodel that included a second pathway, bywhichVMPFCdirectlyinfluenced behavior, which accounted for a larger proportion ofthe variance in behavior than the amygdala/LOC pathway. Oneinterpretation is that, for deletion carriers, the emotionally tunedvividness of perception is more strongly informed by internallygenerated affective experience. We note that, based on this anal-ysis, it is not possible to infer the causal influence of activity in oneregion on another as we could with other methods such as dy-namic causal modeling (Wang et al., 2014).Although they showed greater EEV,ADRA2b deletion carriersrated all stimuli as higher in overall noise than noncarriers. Oneexplanation is that tonic NE activity, thought to be influenced byADRA2b, is sensitive to salience in general (Aston-Jones and Co-hen, 2005), including low-level visual salience. It is possible thatdeletion carriers are more perceptually sensitive to visual sa-lience, resulting in greater sensitivity to the task-relevant overlaid6514 • J. Neurosci., April 22, 2015 • 35(16):6506–6516 Todd et al. • ADRA2b Enhances Perceptual Vividnessnoise, especially when stimuli are not emotionally salient. Indeedour follow-up analysis revealed that deletion carriers showedgreater VMPFC activity in response to contrast. Nonetheless, theEEV results we report here showed activation that passed thresh-old after controlling for variance from visual salience. Thus, indeletion carriers, sensitivity to affective salience influencedVMPFC activation over and above variance accounted for bysensitivity to low-level salience. Thus, whereas deletion carriersmay show greater VMPFC sensitivity to low-level visual features,they also show greater VMPFC sensitivity to EEV.In this sample we found no effect of ADRA2b on emotionalmodulation of memory. This may reflect insufficient power todetect an effect. Previous smaller-N imaging studies have simi-larly failed to find effects of ADRA2b on emotional enhancementof memory (Rasch et al., 2009).5HTTLPRAlthough 5HTTLPR has been implicated in affective biases inattention (Canli, 2008), it did not influence behavioral indices ofEEV. This is consistent with our previous studies in which carry-ing the 5HTTLPR short allele failed to predict affective biases inperceptual encoding or links between encoding and memory(Todd et al., 2013).However, in the present studywe did not havesufficient power to detect any but the strongest behavioral results.Importantly, carrying the short 5HTTLPR allele was associatedwith EEVmodulation of activity in the same region of VMPFC asthat reported for theADRA2bdeletion variant. Carrying the shortallele influences serotonin activity and has been associated withgreater amygdala sensitivity to emotional salience (Munafo` et al.,2008) and altered patterns of connectivity between the amygdalaand ventral PFC (Heinz et al., 2005), which in turn have beenlinked to biases in affective processing. Our finding suggests that,like deletion carriers, short allele carriers’ subjective experience ofemotional stimuli is more intensely colored bymore abstract eval-uations of emotional value. Overall this finding is consistent withevidence that NE and serotonin systems mutually modulate eachother (Sara and Bouret, 2012). Future research can examine poten-tially distinct contributions of ADRA2b and 5HTTLPR to affectivebiasing of specific components of attention (e.g., orienting vs diffi-culty disengaging).One outstanding question concerns whether the enhancedtuning to emotionally salient stimuli that we have observed inADRA2b deletion carriers is due to faster or more intense emo-tional learning. Studies in rodents suggest that, in development,when !2b receptors mature, emotional learning is strongly re-duced (Sullivan and Wilson, 1994). These findings lead to thehypothesis that deletion carriers, who have reduced !2b inhibi-tory function, should show facilitated learning of emotional as-sociations. Future research can specifically test this hypothesis.In conclusion, ADRA2b deletion carriers perceive emotionalaspects of the world more vividly, an experience that is reflectedby overall greater activity in key hubs of valuation networks. Ourdata suggest that commongenetic differences influencingNE andserotonin activity—likely in conjunction with life experience—tune brain and behavior to what we learn to be emotionally impor-tant. Such emotionally enhanced perception may in part explainwhydeletioncarriers are susceptible to intrusivememories followingtrauma (de Quervain and Papassotiropoulos, 2006).NotesSupplemental material for this article is available at http://mclab.psych.ubc.ca/wp-content/uploads/2015/01/ToddEtAl_2015_S u p p l e m e n ta r y . p d f. The supplemental material contains additional results ob-tained from analyses of recognition memory data obtained on-line 1week after images were first encountered in the scanner. 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