The role of primary visual cortex (V1) in visual awareness

In the search for the neural correlate of Visual awareness, much controvers y exists about the role of primary visual cortex. Here, the neurophysiologi cal data from VI recordings in awake monkeys are examined in light of two g eneral classes of models of visual awareness. In the first model type, visu al awareness is seen as being mediated either by a particular set of areas or pathways, or alternatively by a specific set of neurons. In these models , the role of V1 seems rather limited, as the mere activity of V1 cells see ms insufficient to mediate awareness. In the second model type, awareness i s hypothesized to be mediated by a global mechanism, i.e. a specific kind o f activity not linked to a particular area or cell type. Two separate versi ons of global models are discussed, synchronous oscillations and spike rate modulations. It is shown that V1 synchrony does not reflect perception but rather the horizontal connections between neurons, indicating that V1 sync hrony cannot be a direct neural correlate of conscious percepts. However, t he rate of spike discharges of V1 neurons is strongly modulated by perceptu al context, and these modulations correlate very well with aspects of perce ptual organization, visual awareness, and attention. If these modulations s erve as a neural correlate of visual awareness, then VI contributes to that neural correlate. Whether V1 plays a role in the neural correlate of visua l awareness thus strongly depends on the way visual awareness is hypothesiz ed to be implemented in the brain. (C) 2000 Elsevier Science Ltd. All right s reserved.