The neural correlates of conscious visual perception in the frontal cortex of non-human primates

Abstract

In binocular rivalry, our perception alternates spontaneously between mutually exclusive or mixed interpretations, although the physical stimulus remains constant. This enables us to study visual consciousness, as it allows a dissociation of sensory processing and conscious perception. Previous BOLD fMRI studies in humans have implicated the role of the fronto-parietal network in mediating perceptual alternations. However, the extent and the nature of these modulations has been argued to reflect consequences of conscious perception, like introspection, monitoring and, decision making. To resolve this issue, we used a no-report binocular rivalry paradigm of vertically moving gratings, based on an Optokinetic Nystagmus (OKN) read-out of the content of consciousness. We show here for the first time that slow cortical states in the delta-theta (1-9Hz), and beta (20-40Hz) regimes in the prefrontal cortex coupled antagonistically are predictive of an upcoming change only when the percept switches spontaneously, but not physically. Physical transitions in the animal’s percept manifest themselves strongly post-switch in the same oscillatory range. Moreover, we also show a clear dissociation between the change in the polarity of the OKN and this slow-state activity preceding a spontaneous transition. Furthermore, we find robust modulation in the spiking activity of visually-selective simultaneously recorded neuronal ensembles contingent on the animal’s perception. The magnitude of these modulations was comparable to the activity elicited in response to presentation of monocular visual input. Taken together, these results strongly suggest that oscillatory activity in the prefrontal cortex plays a central role in refreshing the content of visual consciousness and spiking activity is modulated in accordance with conscious perception.