CORTICAL FEEDBACK IMPROVES DISCRIMINATION BETWEEN FIGURE AND BACKGROUND BY V1, V2 AND V3 NEURONS

A single visual stimulus activates neurons in many different cortical areas. A major challenge in cortical physiology is to understand how t he neural activity in these numerous active zones leads to a unified p ercept of the visual sct ne. The anatomical basis for these interactio ns is the dense network of connections that link the visual areas. Wit hin this network, feedforward connections transmit signals from lower- order areas such as V1 or V2 to higher-order areas. In addition, there is a dense web of feedback connections which, despite their anatomica l prominence(1,4), remain functionally mysterious(5-8). Here we show, using reversible inactivation of a higher-order area (monkey area V5/M T), that feedback connections serve to amplify and focus activity of n eurons in lower-order areas, and that they are important in the differ entiation of figure from ground, particularly in the case of stimuli o f low visibility. More specifically, we show that feedback connections facilitate responses to objects moving within the classical receptive field; enhance suppression evoked by background stimuli in the surrou nding region; and have the strongest effects for stimuli of low salien ce.