Combined lesions of perirhinal and entorhinal cortex impair rats' performance in two versions of the spatially guided radial-arm maze.

The present study examined the effects of combined lesions of the entorhinal and perirhinal cortex (PRER) on performance of two versions of the spatially guided eigh-tarm radial maze. In the first version, all arms were baited and in each session the rats were allowed to explore the maze freely until they retrieved all of the reinforcers. PRER subjects were profoundly impaired in performance of this task, making fewer correct choices and more total errors than control subjects. In the second task, a delayed nonmatching to sample version of the radial-arm maze, each daily session was separated into two phases. In the first, predelay phase, four arms were open and the remaining four arms were blocked with clear Plexiglas barriers; subjects were permitted to visit each of the four arms and retrieve the reinforcers. In the second, postdelay phase, the subject was placed on the maze with free access to all eight of the arms, but only those arms that were blocked in the predelay phase contained reinforcers. Delays of either 10 min or 30 s separated the pre- and postdelay phases. PRER subjects were significantly impaired in their performance of this task at both delays, making fewer correct choices and more errors than controls; the magnitude of this deficit was not dependent on length of delay. These data suggest that, along with the hippocampal formation, the entorhinal and perirhinal cortices actively participate in the acquisition and performance of appetitively motivated spatial memory tasks.