Enhancement of object representations in primate perirhinal cortex during a visual working-memory task.

We compared single-cell activities in perirhinal cortex (PRh) as well as adjacent visual cortex (area TE) across two tasks. One task required the monkey to identify any stimulus repetition within a sequence of object stimuli. In the other task, the same stimuli were presented, but the monkey didn't have to remember them. PRh responses during the object-memory task were elevated relative to those during the second task. In TE, on the other hand, there were no significant task-related differences in responses. We did not observe task-related differences related to repetition effects in either brain area. The onset of the enhanced signal in PRh during the object-memory task occurred with a latency of 80 ms after the onset of the stimulus response, suggesting that it was the result of top-down feedback.