Lesions of the perirhinal and parahippocampal cortices in the monkey produce long-lasting memory impairment in the visual and tactual modalities.

Compared to normal animals, monkeys with bilateral lesions of the perirhinal and parahippocampal cortices (PRPH lesion) were impaired on both a visual and a tactual version of the delayed nonmatching to sample task. In addition, the memory deficit was long-lasting, as indicated by the finding of a significant deficit when the visual version of the delayed nonmatching to sample task was readministered approximately 2 years after surgery. Animals with PRPH lesions performed normally on discrimination tasks in the visual and tactual modalities. Multimodal and long-lasting memory impairments are defining characteristics of human medial temporal lobe amnesia. Accordingly, these results demonstrate important parallels between the memory deficit associated with PRPH lesions and human medial temporal lobe amnesia. These data, taken together with previous findings, suggest that the perirhinal and parahippocampal cortices play an important role in memory function and that these cortical areas are critical components of the medial temporal lobe memory system.