Modulation of prefrontal cortex activity by information toward a decision rule.

We used fMRI to investigate how the information content of a stimulus influences activity in brain systems that support decision making. Subjects learned decision rules that were based upon the color, shape, or fill pattern of a series of stimuli. Each stimulus was classified by its information content, defined formally by the decision rules it excluded. While activity in dorsolateral prefrontal cortex (dlPFC) increased with increasing stimulus information, activity in the striatum did not. In contrast, within both the striatum and dlPFC, stimuli consistent with the rule evoked greater activity than stimuli inconsistent with the rule. This dissociation indicates that dlPFC supports modification of sets of stimulus-response contingencies while the striatum supports stimulus-specific learning.

Dynamic and strategic aspects of executive processing.

Executive cognitive functions have been postulated to include both dynamic behavioral selection and strategic goal-setting or response preparation. To investigate the relation between these aspects of executive processing, we embedded an event-related oddball paradigm within a blocked design. Subjects responded to infrequent targets presented within a series of standard stimuli that required no response; this task alternated with a visually similar nontask condition. Using functional magnetic resonance imaging (fMRI), we found that a set of brain regions including dorsolateral prefrontal cortex (dlPFC), insular cortex, cingular cortex, and the basal ganglia demonstrated transient activation both to target stimuli and to the onset of task blocks. Within the parietal cortex, there was a dissociation such that the supramarginal gyrus exhibited greater activity to the target stimuli than to block onsets, while the converse pattern was observed in the intraparietal sulcus. Sustained positive activity during task blocks was present in the caudate and supplementary motor area, while sustained negative activity was present in the precuneus and medial parietal cortex. We conclude that dlPFC and related brain regions mediate both dynamic and strategic processing, through the preparation and selection of rules for behavior.