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Brock M Carlson, Michele A Cox, Kacie Dogherty, Alexander Maier; V1 Laminar Activation during Binocular Rivalry Flash Suppression. Journal of Vision 2019;19(10):64. doi: https://doi.org/10.1167/19.10.64.
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© ARVO (1962-2015); The Authors (2016-present)
When observers continuously view a stimulus in one eye and then an incompatible second stimulus appears in the other eye, their perception invariably switches from the initial stimulus to the second stimulus. Curiously, reversing the presentation order of the two stimuli in this phenomenon (termed binocular rivalry flash suppression) reliably causes an entirely different perceptual state, despite identical retinal stimulation. fMRI studies have found large congruence between primary visual cortex (V1) responses and perceptual state. In contrast, neurophysiology studies have found only a small fraction of V1 neurons that correlate with the perceptual outcome of flash suppression. This apparent discrepancy could be explained if flash suppression evokes a dissociation between neuronal inputs (synaptic activity) and neuronal outputs (spiking). To test this hypothesis, we recorded laminar neuronal responses in V1 of two awake behaving macaques that we exposed to stimulus sequences evoking binocular rivalry flash suppression. We specifically focused on estimating the laminar build-up and decay of synaptic activity using Current Source Density (CSD), a quantitative measurement of localized net depolarization. We found that binocular rivalry flash suppression profoundly affects the laminar profile of CSD. This modulation included the initial volley of activation in the granular layers, which receive the bulk of geniculate inputs. Both matching binocular stimuli, which do not elicit binocular rivalry flash suppression, and incongruent binocular stimuli, which can evoke flash suppression, evoked larger activity than monocular stimulation. However, binocularly incongruent stimuli yielded a larger magnitude of CSD response compared to binocularly congruent stimuli, suggesting that stimulus conflict between the two eyes increases V1 synaptic activation. We show that V1’s laminar profile of synaptic activity is significantly altered during flash suppression, providing important clues as to the underlying mechanisms that lead to perceptual effect during flash suppression.
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