UBC Theses and Dissertations
The lateral prefrontal cortex supports an integrated representation of task-rules and expected rewards : evidence from fMRI-adaptation Dixon, Matt Luke
Our capacity for self-control is supported by the use of behaviour-guiding rules. A fundamental question is how we decide which one of out of many potential rules to follow. If different rules were integrated with their expected reward-value, they could be compared, and the one with the highest value selected. However, it currently remains unknown whether any areas of the brain perform this integrative function. To address this question, we took advantage of functional magnetic resonance imaging (fMRI)-adaptation—the ubiquitous finding that repeated as compared to novel stimuli elicit a change in the magnitude of neural activity in areas of the brain that are sensitive to that stimulus. We created a novel fMRI-adaptation paradigm in which instruction cues signaled novel or repeated task-rules and expected rewards. We found that the inferior frontal sulcus (IFS)—a sub-region of the lateral prefrontal cortex—exhibited fMRI-adaptation uniquely when both rule and reward information repeated as compared to when it was novel. fMRI-adaptation was not observed when either factor repeated in isolation, providing strong evidence that the IFS supports an integrated representation of task-rules and rewards. Consistent with an integrative role, the IFS exhibited correlated activity with numerous rule-related and reward-related areas of the brain across the entire experimental time-course. Additionally, the correlation strength between the IFS and a subset of these regions changed as a function of the novelty of rule and reward information presented during the instruction cue period. Our results provide novel evidence that the IFS integrates rules with their expected reward-value, which in turn can guide complex decision making.
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