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 in 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. We find that hit trials are characterized by a behavioral state with increased arousal and improved eye position stability. During hit trials, target stimuli evoke stronger responses in V4, and excitatory neurons in the superficial layers, the primary feed-forward output of the cortical column, exhibit lower variability. Hit trials are characterized by greater synchrony between the output layers of the cortex during spontaneous activity, while the stimulus evoked period shows 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.