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

Lesions placed in the rostral perirhinal cortex (rPRh) after fear conditioning interfere with the expression of conditioned fear responses elicited 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 effects when animals are tested in the conditioning context. Two days after male rats received classical fear conditioning, involving the pairing of an auditory conditioned stimulus (CS) with footshock, bilateral electrolytic lesions were produced in the rPRh. Five days later conditioned freezing behavior was measured during a 60-s exposure to the CS in a novel context and then 1 hr later in the conditioning context. There were 3 major findings. First, rPRh-lesioned animals froze significantly less than controls to the CS in the novel context, thus confirming previously reported findings. Second, rPRh-lesioned animals also froze less than controls to the CS in the conditioning context, but froze significantly more to the CS in the conditioning than in the novel context, suggesting that at least part of the deficit in the novel context is due to the absence of contextual cues. Third, animals with rPRh lesions froze significantly less than controls to the conditioning context itself. This latter finding suggests that rPRh lesions interfere 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 results support the hypothesis that the perirhinal cortex is an important brain region for memory processes and may be especially involved in the use of contextual cues as retrieval aids.