Feedback processing in monkey visual cortex

Our perception is an inherently active process. We dynamically select information that is behaviorally relevant for us at given moments in time, enabling us to interact effectively with the world around us. This ability is thought to depend on feedback from higher cortical areas to early sensory areas, but this process remains poorly understood. One issue in investigating feedback processing is that it is generally activated at the same time as feedforward processing, making it hard to distinguish one from the other. However, feedforward and feedback connections target separate layers in the cortex, providing a way to disentangle the two processing streams.
We trained monkeys on different cognitive tasks and recorded simultaneously in the different layers of monkey primary visual cortex (V1). First, we found a robust effect of both attention and working memory on spiking activity in V1. The working memory signal could be abolished with a mask, but reappeared at a later point in time. This suggests that V1 is not only involved in the selection of task relevant information, but also in the maintenance of that information when the stimulus is no longer present. Furthermore, we found that attention and working memory gave rise to feedback signatures corresponding to the modulation of spiking activity and synaptic input to V1. Finally, we trained monkeys to recognize a pattern of visual stimuli. This will allow us to investigate the effect on different cortical layers when a stimulus was expected to arrive, and the error signals when this expectation was violated.
These findings provide new insights in the laminar circuits involved in top-down modulation of activity in early visual cortex when a visual stimulus is present, when a stimulus was present, and when a stimulus is expected to appear.