Rats with hippocampal, perirhinal cortex and postrhinal cortex lesions were trained in a reference spatial memory task to determine whether these structures contribute differentially to the acquisition and retention of spatial information. The results of Experiment 1 indicated that hippocampal lesions profoundly impaired the acquisition of the task. However, postrhinal lesions produced only a mild deficit and perirhinal lesions produced no deficit whatsoever in the learning of the task. During acquisition, hippocampus-damaged rats committed more perseverative errors than postrhinal rats, suggesting that the nature of the operations performed by each of these structures is different. The results of Experiment 2 showed a profound deficit in retention in hippocampal and postrhinal-lesioned animals tested 24 days after training. Perirhinal-lesioned animals, however, executed the task just as well as the control subjects did. These functional data, in consonance with existing connectivity data, suggest that each of these medial temporal lobe regions makes a different contribution to allocentric spatial learning and memory.
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