When is the perirhinal cortex necessary for the performance of spatial memory tasks?

The perirhinal cortex and hippocampus have close anatomical links and it has, therefore, been proposed that they have important, coordinated roles in memory. This review examines the relative role of these structures in spatial memory tasks that are known to be hippocampal-dependent. The published lesion data gives a mixed picture, as only some studies detect spatial deficits after perirhinal cortex lesions. The possible reasons for these inconsistencies are reviewed, along with electrophysiological data that indicate how perirhinal cortex lesions may alter neuronal activity in the hippocampus. Overall, the disruptive effects of perirhinal lesions on spatial memory performance are, when they occur, typically transient and never as severe as those seen after hippocampal lesions. It is argued that parallel cortical routes provide key, sensory data to the hippocampus such that in the absence of the perirhinal cortex alternative information is available. The deficits associated with perirhinal damage may then reflect difficulties that arise when task performance requires the use of ambiguous distal cues, for example, those containing overlapping visual features.