The Role of Layer 6 Feedback Cells in the Primary Visual Cortex

Abstract

The abiding challenge in vision is to unravel the role of the extensive feedback systems that parallel the ascending feed-forward pathways. Feed-forward projections in the cerebral cortex, which transmit bottom-up information away from sensory receptors, are matched by feedback projections that can transmit top-down signals. The role of layer 6 feedback cells in visual processing is of particular appealing for those cells in the visual cortex sit in a crucial place in the circuitry involved in the early processing of the visual input in higher mammals such as cats and primates [1,2,3]. They make connections that straddle both the relay of information from retinal afferents to LGN cells and the transfer of information from LGN cells to layer 4 of the visual cortex. In simple numerical terms the connections from layer 6 cells to LGN and layer 4 of the visual cortex greatly exceed the contribution from the axons carrying the ascending input [5,4,6,7,8}. This suggests that layer 6 cells play a special role in controlling the access of the visual input to the cortex. The question is what is this role?