SignificanceWhether the population activity in neuronal networks can be understood as the sum of individual activities or neurons jointly determine the state of populations is a fundamental question of neuroscience. Spike count correlations reflect coordination between pairs of neurons and therefore can be regarded as a signature of joint computations. So far, a majority of experimental and theoretical analyses considered these correlations noise and ignored stimulus-dependent aspects. Based on theoretical considerations, we argue that spike count correlations are stimulus dependent and variations in their structure can be predicted by stimulus content. Recording the activity of neurons from primary visual cortex in task-engaged monkeys, we confirm these predictions. These results provide insight into the computations performed by populations of cortical neurons.
When a visual stimulus is repeated, average neuronal responses typically decrease, yet they might maintain or even increase their impact through increased synchronization. Previous work has found that many repetitions of a grating lead to increasing gamma-band synchronization. Here we show in awake macaque area V1 that both, repetition-related reductions in firing rate and increases in gamma are specific to the repeated stimulus. These effects showed some persistence on the timescale of minutes. Further, gamma increases were specific to the presented stimulus location. Importantly, repetition effects on gamma and on firing rates generalized to natural images. These findings suggest that gamma-band synchronization subserves the adaptive processing of repeated stimulus encounters, both for generating efficient stimulus responses and possibly for memory formation.
Summary
When a visual stimulus is repeated, average neuronal responses typically decrease, yet they might maintain or even increase their impact through increased synchronization. Previous work has found that many repetitions of a grating lead to increasing gamma-band synchronization. Here, we show in awake macaque area V1 that both repetition-related reductions in firing rate and increases in gamma are specific to the repeated stimulus. These effects show some persistence on the timescale of minutes. Gamma increases are specific to the presented stimulus location. Further, repetition effects on gamma and on firing rates generalize to images of natural objects. These findings support the notion that gamma-band synchronization subserves the adaptive processing of repeated stimulus encounters.
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