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

Neurophysiological data from V1 recordings in awake monkeys were examined in light of 2 general classes of visual awareness (VA)models. In model type 1, VA 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 limited, as the mere activity of V1 cells seems insufficient to mediate VA. In model type 2, VA is hypothesized to be mediated by a global mechanism, i.e. a specific kind of activity not linked to a particular area or cell type. Two separate versions 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 synchrony cannot be a direct neural correlate of conscious percepts. However, the rate of spike discharges of V1 neurons is strongly modulated by perceptual context, and these modulations correlate very well with aspects of perceptual organization, VA, and attention. If these modulations serve as a neural correlate of VA, then V1 contributes to that neural correlate. Whether V1 plays a role in the neural correlate of VA thus strongly depends on the way VA is hypothesized to be implemented in the brain.