The functional organization of directionally biassed feedback influences from MT to V1 and the LGN

In the brain the pathways transferring sensory information from the sense organs, such as the eyes, to higher centers are matched by feedback pathways that run in the opposite direction. Thus the input from the eyes is relayed via a structure called the visual thalamus to the visual cortex, but the visual cortex sends feedback connections back down to the visual thalamus. Indeed numerically these exceed those arising from the eyes. Why does this happen? What do these connections do? They seem to bring the knowledge from the processing at higher levels in the brain back to earlier levels and in some way use this to enhance our ability to perceive the world around us. Here we are probing the role of the higher cortical area concerned with processing motion in the visual world and the way this area is linked into a functional circuit with the primary visual cortex and thalamus. The suggestion is that the feed forward and feedback connections linking three levels in the visual system operate as an integrated whole rather than as separate steps in a sequence.

The objective of this proposal is to advance our understanding of the functional organisation of feedback effects from the motion area MT/V5 to the LGN via V1. It tests the hypothesis that feedback from MT exerts a potent and structured influence down the neuraxis on the way cells respond to moving stimuli and directional context. In so doing it proposes the further hypothesis that MT is an integral component of the circuitry determining the moment by moment dynamics of visual processing in an iterative process in the interplay between all levels in the system. We provide preliminary data that give strong evidence in support of both hypotheses and propose experiments that dissect the organization of the processes driven by MT.