Effects of selective perirhinal and postrhinal lesions on acquisition and retention of a visual discrimination task in rats.

The hippocampal region along with rhinal structures seems to support learning and memory in an important manner. Structures adjacent to the rhinal fissure in the rat have recently been suggested to be divided into the perirhinal and postrhinal cortices. Some effects of perirhinal lesions on cognitive processing are known, whereas effects of postrhinal lesions appear to be unknown. The purpose of the present study was to examine the relative effects of perirhinal and postrhinal lesions in a three-choice visual discrimination test. The results show that both types of lesions impaired acquisition of the task, but only perirhinal lesions impeded subsequent retention. Because the initial phase of acquisition was unaffected by both lesions, it is suggested that the deficits observed may be of mnemonic nature. The apparent differential involvement of the perirhinal cortex and postrhinal cortex in cognition may be associated with differences in anatomical connectivity among these structures.