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Zusammenfassung:
Understanding the neural underpinnings of conscious perception has long intrigued the students of the brain from philosophers to modern neuroscientists. In the visual domain, the primary visual cortex (V1) is by far the most extensively studied cortical area. It entails the main gateway of visual information to higher cortical areas and we understand a lot about its function in sensory processing. Nevertheless, the role of V1 in perceptual awareness remains intensely debated. Under certain stimulus conditions perception alternates between two or multiple stimulus interpretations. Notably such perceptual alternations happen while the sensory input is kept constant, offering thus a clear dissociation of sensory stimulation and subjective awareness. A celebrated example of such a perceptual phenomenon is binocular rivalry (BR). It involves the dichoptic presentation of two different stimuli at corresponding retinal locations and results in the perceptual suppression of one of the two stimuli at different times. A slight variant of BR, binocular flash suppression (BFS), ensures excellent control over the subjects’ perceptual state by intermittent presentation of monocular and binocular stimuli. We have trained rhesus macaques to report their perception during BFS and BR to study the effects of perceptual suppression in V1. We have recorded the spiking activity of a large number of well isolated single units (SUA) and acquired simultaneous local field potentials (LFPs) during the dichoptic presentation of orthogonal orientation gratings. We found that during BFS, 20 of the single units modulated their activities in consonance with the perceptual state. Furthermore, the magnitude of the perceptual effect was small (15) in comparison to the sensory preference of the neurons. Analysis of the ocularity preferences demonstrated that both monocular and binocular classes of cells show perceptual modulations with equal probability. In addition, cells modulating during perceptual suppression encode information matching their sensory preferences and therefore can be used for decoding both the orientation and/or the eye of presentation of the perceived grating. Results of the LFPs were very similar to the single units showing a similar percentage of sites modulating with perception in all analyzed frequency bands. We conclude that footprints of perception are evident in both the SUA and LFP signals in V1 but in a much smaller degree than their corresponding sensory selectivity. Perceptual states might have a modulatory role on more intricate aspects of V1 firing patterns, not necessarily altering the firing rates of single cells or the LFP power dramatically.
