Perisynaptic activity in the prefrontal cortex reflects spontaneous transitions in conscious visual perception

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 for a dissociation between sensory processing and conscious perception [1]. Previous imaging studies in humans have implicated the role of the fronto-parietal network in mediating perceptual alternations [2]. However, whether this frontal activation is indeed related to the percept, or, rather is confounded by, or reflects the consequences of perception viz. decision-making, introspection or motor-output, is still a matter of debate [3, 4]. Moreover, the degree of modulation in the frontal regions at the spiking and perisynaptic activity timescales is yet unclear. Because of the above-mentioned considerations, two male macaques were trained to maintain fixation within a window and follow the motion of the stimulus for up to 12 seconds in a specifically designed no-report paradigm. They were implanted with Utah Arrays (10 × 10) in the ventro-lateral prefrontal cortex. Spontaneous switches in the percept were identified from the Optokinetic Nystagmus traces. Trials where the stimulus was experimentally switched acted as a control. Sites on the array were sorted according to their preference for either an upwardmoving or a downward-moving stimulus based on the spiking activity. In the high-frequency regime, i.e. the Gamma band (80–150 Hz), the power followed the pattern of selectivity displayed by the neural discharges including adaptation as reported previously [4]. Activity preceding a spontaneous switch revealed epochs of power modulations in the low-frequencies, i.e. the Delta Band (1–4 Hz) and the Theta Band (4–8 Hz), whereas this activity manifested itself strongly post-switch during physical alternation, pointing towards a role of slow cortical states in refreshing the content of conscious visual perception. Moreover, this burst-like activity was stronger when a preferred stimulus switched to a non-preferred stimulus implicating these slow cortical states in specifically overcoming an energy barrier required to transition from a preferred to a non-preferred stimulus. Taken together, these results strongly suggest that oscillatory activity in the prefrontal cortex plays a central role in the spontaneous transitions in conscious visual perception