Perirhinal cortex neuronal activity is actively related to working memory in the macaque

Lesion studies suggest that the perirhinal cortex plays a role in object recognition memory. To analyze its role, we recorded the activity of single neurons in the perirhinal cortex in a rhesus monkey (Macaca mulatta) performing a delayed matching-to-sample task with up to four intervening stimuli. Certain neurons (40 of 90 analyzed) showed a smaller response to an image when it was shown the second time within a trial (as a match image) than when it had been shown (as a sample image) the first time. A new finding was that the perirhinal cortex neurons were actively reset between trials: when a particular image was shown as a sample on a succeeding trial, the response was much larger than when it had been shown as a match image a short time previously on the previous trial. This resetting between trials appears to reflect the operation of an active working memory process rather than a passive temporal decay in a neuronal response. The results thus provide evidence that the perirhinal cortex plays an active role in visual working memory, perhaps in association with other brain areas such as the prefrontal cortex.