Entorhinal-perirhinal lesions impair performance of rats on two versions of place learning in the Morris water maze.

The effects of entorhinal-perirhinal lesions in rats were studied with 2 versions of a place learning task in the Morris water maze. These lesions impaired performance on a multiple-trial task (3 days of 6 trials and a probe trial). This assessment was followed by a task in which rats were repeatedly trained to find novel locations with a variable delay (30 s or 5 min) imposed between each sample trial and retention test. Entorhinal-perirhinal damage produced a delay-dependent deficit in spatial memory: Rats with lesions were impaired at the 5-min delay relative to the control group and to their own performance at 30 s. These findings are discussed in relationship to memory impairment after entorhinal damage and spatial learning deficits observed after hippocampal damage.