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要旨:
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.
