A neural circuit analysis of visual recognition memory: Role of perirhinal, medial, and lateral entorhinal cortex

Using a continuous recognition memory procedure for visual object informati on, we sequentially presented rats with eight novel objects and four repeat ed objects (chosen from the 8). These were selected from 120 different thre e-dimensional objects of varying sizes, shapes, textures, and degree of bri ghtness. Repeated objects had lags ranging from 0 to 4 (from 0 to 4 differe nt objects between the first and repeated presentation). An object was pres ented on one side of a lone; table divided in half by an opaque Plexiglas g uillotine door, and the latency between opening the door and the rat moving the object was measured. The first presentation of an object resulted in r einforcement, but repeated presentations did not result in a reinforcement. ,After completion of acquisition training (significantly longer latencies f or repeated presentation compared with the first presentation of an object) , rats received lesions of the perirhinal, medial, or lateral entorhinal co rtex or served as sham operated controls. On the basis of postsurgery testi ng and additional tests, the results indicated that rats with perirhinal co rtex lesions had a sustained impairment in performing the task. There were no sustained deficits with medial or lateral entorhinal cortex lesions. The data suggest that recognition memory for visual object information is medi ated primarily by the perirhinal cortex but not by the medial or lateral en torhinal cortex.