DISSOCIABLE FORMS OF INHIBITORY CONTROL WITHIN PREFRONTAL CORTEX WITHAN ANALOG OF THE WISCONSIN CARD SORT TEST - RESTRICTION TO NOVEL SITUATIONS AND INDEPENDENCE FROM ONLINE PROCESSING

Attentional set-shifting and discrimination reversal are sensitive to prefrontal damage in the marmoset in a manner qualitatively similar to that seen in man and Old World monkeys, respectively (Dias et al., 19 96b), Preliminary findings have demonstrated that although lateral but not orbital prefrontal cortex is the critical locus in shifting an at tentional set between perceptual dimensions, orbital but not lateral p refrontal cortex is the critical locus in reversing a stimulus-reward association within a particular perceptual dimension (Dias et al., 199 6a). The present study presents this analysis in full and extends the results in three main ways by demonstrating that (1) mechanisms of inh ibitory control and ''on-line'' processing are independent within the prefrontal cortex, (2) impairments in inhibitory control induced by pr efrontal damage are restricted to novel situations, and (3) those pref rontal areas involved in the suppression of previously established res ponse sets are not involved in the acquisition of such response sets. These findings suggest that inhibitory control is a general process th at operates across functionally distinct regions within the prefrontal cortex. Although damage to lateral prefrontal cortex causes a loss of inhibitory control in attentional selection, damage to orbitofrontal cortex causes a loss of inhibitory control in affective processing. Th ese findings provide an explanation for the apparent discrepancy betwe en human and nonhuman primate studies in which disinhibition as measur ed on the Wisconsin Card Sort Test is associated with dorsolateral pre frontal damage, whereas disinhibition as measured on discrimination re versal is associated with orbitofrontal damage.