Dissociation in retrograde memory for object discriminations and object recognition in rats with perirhinal cortex damage

This experiment examined the effects of perirhinal cortex (PeRh) lesions on rats' retrograde memory for object-discriminations and retrograde object recognition. Rats learned one discrimination problem or five concurrent discrimination problems 4 weeks before surgery, and a new problem or five new problems during the week preceding surgery. Each rat was also familiarized with a sample object in an open field, 5, 3, or 1 week before surgery. PeRh-lesioned rats displayed normal retention of the object discrimination problems, but on a test of novelty preference they showed evidence of impaired recognition of the sample objects. A similar dissociation was observed on anterograde tests of object-discrimination learning and object recognition. The findings suggest the perirhinal cortex plays an essential role in rats' ability to discriminate the familiarity of objects previously encountered either before or after surgery, but this ability may not be essential for accurate performance of a simple object-discrimination task.