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

In order to investigate the respective roles of dorsal and ventral parts of the medial prefrontal cortex (mPFC) on a delayed alternation task, the acq uisition of which is disrupted by large mPFC lesions (Winocur, 1991), rats with circumscribed lesions to the anterior cingulate (ACd) or the prelimbic -infralimbic (PL-IL) cortex were compared. As was predicted, ACd lesions se verely impaired performance, and an analysis of the results suggests an inv olvement of this region in sequencing temporally ordered behavior. On the o ther 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 dif ference between the tasks related to the scheduling of critical delays. Whe reas in the previous experiment, delay intervals were increased progressive ly 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 proce dure that required less response adjustment. Under these conditions, the PL -IL group performed normally, as in Experiment 1. Taken together, the resul ts provide evidence that the PL-IL cortex is implicated in processes that s upport attentional mechanisms and behavioral flexibility. Overall, the pres ent results support the general hypothesis of subregionalization of mPFC fu nctions.