Modulation of neuronal responses in macaque primary visual cortex in a memory task.

The primary visual cortex, a relatively early station in the visual pathway, has long been considered mainly as a site of basic feature detection but evidence is emerging that is consistent with the existence of feedback influences from higher cortical areas. We show that in a delayed match-to-sample memory task, where the monkey needs to remember both the visual pattern and its location, there is significant modulation of neuronal activity in the primary visual cortex suggestive of a feedback signal. Responses to identical patterns are remarkably different depending upon their place in the memory task. These modulatory influences are significantly less when the same visual patterns are shown during a simple fixation task, where these stimuli can be ignored and not attended to. The results indicate that neural processing specific to attentional and mnemonic functions can involve even primary sensory areas.