Flexible perceptual encoding by discrete gamma events

Cognitive processes underlying behaviour are linked to specific spatiotemporal patterns of neural activity in the neocortex1-6. These patterns arise from synchronous synaptic activity7 and are often analysed as oscillations, but may also display aperiodic dynamics that are not well detected. Here we develop a novel analytical method decomposing patterned activity into discrete network events and use this approach to track gamma activity (30-80 Hz) in the mouse visual cortex (V1). We find that the gamma event rate varies with arousal and individual events can cluster in brief oscillatory bouts but also occur in isolation. Individual events synchronize neural firing across layers and promote enhanced visual encoding. V1 gamma events are evoked by patterned input from the dorsal lateral geniculate nucleus (dLGN) and suppressed by optogenetic modulation of the dLGN, suggesting that they support thalamocortical integration of visual information. In behaving mice, the gamma event rate increases steadily before visually cued behavioural responses, predicting trial-by-trial performance. Suppressing V1 gamma events impairs visual detection performance, whereas evoking them elicits a behavioural response. This relationship between gamma events and behaviour is sensory modality specific and rapidly modulated by changes in task objectives. Gamma events thus support a flexible encoding of visual information according to behavioural context.