The role of prelimbic cortex in instrumental conditioning

Abstract

Numerous studies have implicated human and primate prefrontal cortex in the ability to hold and manipulate goal or outcome-related information in working memory to guide the performance of forthcoming actions. Here we report that cell-body lesions of prelimbic cortex impair the ability of rats to select an action based on previously encoded action–outcome associations. Rats were food deprived and trained to press two levers, one delivering food pellets and the other a sucrose solution. All rats acquired the lever-press response although the initial acquisition in the prelimbic rats was significantly slower than in sham controls. Furthermore, whereas in sham-lesioned rats, post-training devaluation of one of the two outcomes using a specific satiety procedure produced a selective reduction in performance on the lever that in training delivered the prefed outcome, prelimbic rats failed to show a selective devaluation effect and appeared to reduce performance on both levers non-selectively. Importantly, this impairment only emerged in extinction; in subsequent experiments it was found that, when a specific action–outcome association was cued either by presentation of the outcome itself or by presenting a stimulus previously paired with the outcome, rats demonstrated an ability to select the associated action. These results suggest that action–outcome encoding may be intact in prelimbic rats and that the lesion impaired their ability to retain this learning in working memory in order to establish a course of action. Alternatively, the lesion may have altered the relative contribution of action–outcome and outcome–action associations to instrumental performance. On this account, prelimbic lesions affect action–outcome encoding but leave outcome–action associations intact providing the basis for outcome-mediated initiation of an action sufficient, perhaps, to support acquisition and performance in the lesioned rats.