Functional dissociation between dorsal and ventral regions of the medial prefrontal cortex in rats

Abstract

In order to investigate the respective roles of dorsal and ventral parts of the medial prefrontal cortex (mPFC) on a delayed alternation task, the acquisition of which is disrupted by large mPFC lesions (Winocur, 1991), rats with circumscribed lesions to the anterior cingulate (ACd) or the prelimbicinfralimbic (PL-IL) cortex were compared. As was predicted, ACd lesions severely impaired performance, and an analysis of the results suggests an involvement of this region in sequencing temporally ordered behavior. On the other hand, PL-IL lesions had no effect, a finding that was in contrast with previous evidence that PL-IL lesions induced delay-dependent deficits on a similar task (Delatour & Gisquet-Verrier, 1999). However, an important difference between the tasks related to the scheduling of critical delays. Whereas in the previous experiment, delay intervals were increased progressively in a block design, variable intertrial intervals were a constant feature of training in the present Experiment 1. In Experiment 2, rats with PL-IL lesions were administered Delatour and Gisquet-Verrier’s (1999) alternation task, but modified to incorporate Winocur’s (1991) variable-interval procedure that required less response adjustment. Under these conditions, the PL-IL group performed normally, as in Experiment 1. Taken together, the results provide evidence that the PL-IL cortex is implicated in processes that support attentional mechanisms and behavioral flexibility. Overall, the present results support the general hypothesis of subregionalization of mPFC functions.