Project 3: Neural Mechanisms for Executive Control of Recall

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During the previous funding period, our laboratory has made great progress identifying and characterizing neural correlates of the recall of stored memories. But an important facet of memory remains almost wholly unknown: the "executive control" over memory recall. Having identified candidate neural structures and mechanisms, we are now ready to address this issue. In our proposed project, we aim to address the most fundamental question about executive control of recall, its functional organization. To do so, we will compare and contrast the time-course of neural correlates of the recall of task demands with a behavioral measure of recall: switch costs. Switch costs are seen when subjects must flexibly alternate between performing different, often incompatible, judgments and thus must repeatedly recall and update their internal representations of task demands. Switch costs are increases in reaction time (RT) and errors whose magnitude depends on the time between a cue to switch tasks and task initiation. Thus, switch costs reflect the time needed for a set of rules to be recalled from memory and supplant a set of rules already held "on-line". By comparing neural dynamics of recall with switch costs, we can determine the relationship between this activity and its impact on behavior. We will examine neural activity in brain areas where we have previously identified neural correlates for the recall of task demands: the prefrontal cortex, premotor cortex, and basal ganglia. We found differences in latencies and other neural properties between these areas that suggest different roles in recall. Comparing these properties to a behavioral measure of recall will allow us to tease apart their respective contributions. Monkeys will switch between discriminating the color and orientation; we have already found switch costs in monkeys trained under a similar paradigm. Because executive control over recall and other brain processes is central to intelligent behavior, data from this project has the potential to impact on a wide range of behaviors and human disorders. Executive control is disrupted in a variety of neuropsychiatric disorders such as autism and schizophrenia. By identifying brain structures important for these abilities, discerning their relative roles, and uncovering their neural mechanisms, we can open a path to drug and behavioral therapies designed to alleviate dysfunctions of executive control.