SUBTOTAL PERIRHINAL CORTEX LESIONS INCREASE EXPLORATORY-BEHAVIOR IN THE RAT WITHOUT PRODUCING DEFICITS IN THE MORRIS WATER MAZE

Rats with bilateral, subtotal lesions of the superficial layers of per irhinal cortex were tested in a reaction-to-novelty procedure and in t he Morris water maze. Lesioned rats spent significantly more time than did control animals in exploring objects in the reaction-to-novelty t est apparatus. In addition, lesioned rats exhibited increased rearing, both in the exploration procedure and in an open field test. Locomoto r and grooming activity in lesioned rats was not significantly differe nt from that of control animals. These results suggest that, in the ra t, the perirhinal cortex may be involved in the modulation of explorat ory behavior, possibly via links with the amygdala. Lesioned rats were not impaired in the Morris water maze; rather, their latencies to fin d the hidden platform were significantly lower than those of control a nimals during initial place navigation testing. The latter finding con trasts with the results of our previous work, which demonstrates that more extensive lesions of perirhinal cortex produce water maze deficit s.