Deficits in executive processing, defined as the ability to adjust behavior based upon goals and context, have severe consequences for human thought and behavior. In drug abusers, executive processing impairments are manifest in problems with representing the consequences for actions and with inhibiting responses to inappropriate stimuli. This proposal uses functional neuroimaging to investigate the brain mechanisms of executive processing, including how people form and maintain plans for behavior and how they change those plans based upon new information. The proposed experiments will use a novel task designed to separate components of executive processing. The stimulus set will consist of shapes that vary in color and pattern. Subjects will learn rules (e.g., """"""""red items"""""""") that partition the set into targets and non-targets. As in the common Wisconsin Card Sorting Task (WCST), the task rules will change infrequently, so that subjects must form new representations of the task rules. However, unlike in the WCST, subjects will not respond to every stimulus, so that selecting which rule to follow can be dissociated from selecting a response. A combination of neuroimaging measures will be employed, within the same task, to investigate the location and timing of activity associated with different aspects of executive processing. Functional magnetic resonance imaging (fMRI) will be used to identify brain regions associated with learning rules, maintaining learned rules, selecting a new rule, and selecting responses. Scalp-recorded ERP measures will serve to constrain the fMRI results while providing information about the timing of neural events. This research program will inform studies of executive processing, while providing proof-of-concept data for future applications for research support.
