The role of the prefrontal cortex in stimulus guided behavior: An EEG study of young, older, and frontal brain damaged adults.

摘要

Prefrontal Cortex (PFCx) has been implicated in distinct executive control processes. In this study we examined the role of PFCx mediated processes in determining stimulus guided behavioral performance. We studied young (YC) and older (OC) adults as well as patients with either Lateral (LPFCx) or Orbital (OPFCx) Prefrontal Cortex damage in a letter discrimination task. Specifically, we used Electroencephalograpy (EEG) to observe changes in Event Related Potentials (ERPs) related to preparatory attention and action monitoring. The Contingent Negative Variation (CNV) was used to study preparatory attention while the Error Related Negativity (ERN) and Correct Related Negativity (CRN) were used to study action monitoring. Preparatory attention is defined as the process by which PFCx primes task relevant cortical areas for sensory processing and response selection. Action monitoring is the process that updates behavioral strategy.;In experiment one we investigated the role of the preparatory attention in determining response performance in young adults. Experiment two was designed to test the effects of normal aging on PFCx mediated processes and response performance. Finally, in experiment three we characterized the effects of LPFCx and OPFCx damage on PFCx mediated preparatory attention and action monitoring processes.;In summary, temporary lapses in preparatory attention lead to deficient sensory processing and incorrect responses. Similarly, defective action monitoring processes, like those observed in older adults, lead to dysfunction in top-down learning and decreased accuracy. Older adults engage bottom-up processes to compensate for their deficits in action monitoring and top-down learning. Dysfunction in both preparatory attention and action monitoring, as is the case with patients with LPFCx damage, leads to disorganized behavior and severe performance deficits. In addition, we found that the OPFCx, via connections to a bottom-up network, is responsible for reorienting attention to the most behaviorally relevant goal when conflict occurs due to added network activity associated with either an internal stimulus (activity associated an irrelevant thought) or an external stimulus (presentation of an unpredicted, irrelevant, arousing, emotional, or novel stimulus). We observed activation of this bottom-up network in young adults in the form of increased frontal polar potentials following an incorrect response; in OC as enhanced frontal potentials during early learning as well as in an absence of the correct versus error difference in preparatory attention at frontal sites during the prestimulus time interval; and in OPFCx patients in the form of increased action monitoring potentials. This OPFCx mediated bottom-up network determines response performance when top-down processes fail to effectively predict the anticipated stimulus. (Abstract shortened by UMI.)