DISRUPTIVE EFFECTS OF POSTTRAINING PERIRHINAL CORTEX LESIONS ON CONDITIONED FEAR - CONTRIBUTIONS OF CONTEXTUAL CUES

Lesions placed in the rostral perirhinal cortex (rPRh) after fear cond itioning interfere with the expression of conditioned fear responses e licited by auditory and visual conditioned stimuli when these stimuli are presented in a context that differs from the conditioning context. The present study examined whether lesions of the rPRh have similar e ffects when animals are tested in the conditioning context. Two days a fter male rats received classical fear conditioning, involving the pai ring of an auditory conditioned stimulus (CS) with footshock, bilatera l electrolytic lesions were produced in the rPRh. Five days later cond itioned freezing behavior was measured during a 60-s exposure to the C S in a novel context and then 1 hr later in the conditioning context. There were 3 major findings. First, rPRh-lesioned animals froze signif icantly less than controls to the CS in the novel context, thus confir ming previously reported findings. Second, rPRh-lesioned animals also froze less than controls to the CS in the conditioning context, but fr oze significantly more to the CS in the conditioning than in the novel context, suggesting that at least part of the deficit in the novel co ntext is due to the absence of contextual cues. Third, animals with rP Rh lesions froze significantly less than controls to the conditioning context itself. This latter finding suggests that rPRh lesions interfe re with contextual processing and that the improvement of performance in the conditioning context might have been even greater had lesioned animals been able to fully process contextual cues. Together, the resu lts support the hypothesis that the perirhinal cortex is an important brain region for memory processes and may be especially involved in th e use of contextual cues as retrieval aids.