Biology subjects

Nandy, A. S.

Publications and source records attributed to Nandy, A. S..

2 recordsLinked to original sources

bioRxiv2021

Brain state and cortical layer-specific mechanisms underlying perception at threshold

Identical stimuli can be perceived or go unnoticed across successive presentations, producing divergent behavioral outcomes despite similarities in sensory input. We sought to understand how fluctuations in behavioral state and cortical layer and cell-class specific neural activity underlie this perceptual variability. We analyzed physiological measurements of state and laminar electrophysiological activity in visual area V4 while monkeys were rewarded for correctly reporting a stimulus change at perceptual threshold. Hit trials were characterized by a behavioral state with heightened arousal, greater eye position stability, and enhanced decoding performance of stimulus identity from neural activity. Target stimuli evoked stronger responses in V4 in hit trials, and excitatory neurons in the superficial layers, the primary feed-forward output of the cortical column, exhibited lower variability. Feed-forward interlaminar population correlations were stronger in hits. Hit trials were further characterized by greater synchrony between the output layers of the cortex during spontaneous activity, while the stimulus-evoked period showed elevated synchrony in the feed-forward pathway. Taken together, these results suggest that a state of elevated arousal and stable retinal images allow enhanced processing of sensory stimuli, which contributes to hits at perceptual threshold.

neuroscience↗

bioRxiv2021

Canonical retinotopic shifts under an inverse force field explain predictive remapping

Predictive remapping -- the ability of cells in retinotopic brain areas to transiently exhibit spatio-temporal retinotopic shifts beyond the spatial extent of their classical receptive fields -- has been proposed as a primary mechanism that stabilizes our percept of the visual world around the time of saccadic eye movements. Despite the well documented effects of predictive remapping, no study to date has been able to provide a mechanistic account of the neural computations and architecture that actively mediate this ubiquitous phenomenon. We propose a novel neurobiologically inspired general model of predictive remapping in which the underlying pre-saccadic attentional and oculomotor signals manifest as three temporally overlapping forces that act on retinotopic brain areas. These three forces - a centripetal one toward the center of gaze, a convergent one toward the saccade target and a translational one parallel to the saccade trajectory - act in an inverse force field and govern the spatio-temporal dynamics of predictive remapping of population receptive fields. The predictions of our model are borne out by the spatio-temporal changes in sensitivity to probe stimuli in human subjects around the time of an eye movement and are consistent with findings of predictive shifts in the receptive fields of cells in the superior colliculus, frontal eye fields, lateral intraparietal area, and visual area V4.

systems biology↗