Areas V1 and V2 show microsaccade-related 3-4 Hz covariation in gamma power and frequency

Neuronal gamma-band synchronization (25-90 Hz) in visual cortex appears sustained and stable during prolonged visual stimulation when investigated with conventional averages across trials. Yet, recent studies in macaque visual cortex have used single-trial analyses to show that both power and frequency of gamma oscillations exhibit substantial moment-by-moment variation. This has raised the question whether these apparently random variations might limit the functional role of gamma-band synchronization for neural processing. Here, we studied the moment-by-moment variation of gamma oscillation power and frequency, as well as inter-areal gamma synchronization by simultaneously recording local field potentials in V1 and V2 of two macaque monkeys. We additionally analyzed electrocorticographic (ECoG) V1 data from a third monkey. Our analyses confirm that gamma-band synchronization is not stationary and sustained but undergoes moment-by-moment variations in power and frequency. However, those variations are neither random and nor a possible obstacle to neural communication. Instead, the gamma power and frequency variations are highly structured, shared between areas, and shaped by a microsaccade-related 3-4 Hz theta rhythm. Our findings provide experimental support for the suggestion that cross-frequency coupling might structure and facilitate the information flow between brain regions. This article is protected by copyright. All rights reserved