RHINAL CORTEX LESIONS AND OBJECT RECOGNITION IN RATS

Rats with bilateral lesions of lateral entorhinal cortex and perirhina l cortex were tested on a nonrecurring-items delayed nonmatching-to-sa mple (DNMS) task resembling the one that is commonly used to study obj ect recognition in monkeys. The rats were tested at retention delays o f 4 s, 15 s, 60 s, 120 s, and 600 s before and after surgery. After su rgery, they displayed a delay-dependent deficit: They performed normal ly at the 4-s delay but were impaired at delays of 15 s or longer. The addition of bilateral amygdala lesions did not increase their DNMS de ficits. The present finding of a severe DNMS deficit following rhinal cortex damage is consistent with the authors' previous finding that bi lateral lesions of the hippocampus and amygdala cause only mild DNMS d eficits in rats unless there is also damage to rhinal cortex (D. G. Mu mby, E. R. Wood, and J. P. J. Pinel, 1992). These findings add to accu mulating evidence that the rhinal cortex, but not the amygdala, plays a critical role in object recognition.