Neurotoxic lesions of the perirhinal cortex do not mimic the behavioural effects of fornix transection in the rat

The effects of perirhinal (Prh) and fornix (Fx) lesions were compared on a series of spatial and nonspatial memory tests. These tests included delayed nonmatching-to-position in an operant chamber, a spatial (lever) discrimination and its subsequent reversals, delayed spatial alternation in a T-maze, and an object recognition memory test using both normal objects and 're configured' objects. As expected, the rats with fornix lesions were impaired on all of the spatial tests. Their performance on the recognition test was, however, left intact. The perirhinal lesions produced a quite different pattern of results. Animals with these lesions were unimpaired on all three spatial tasks, but displayed evidence of an impairment on the object recognition test. This impairment was restricted to the longer delay (15 min) and was only found with the normal objects. These findings suggest that the actions of the perirhinal cortex and the hippocampus can be dissociated from one another.