Simultaneously induced slow and fast gamma waves travel independently in primate primary visual cortex

Abstract

Travelling waves have been reported for multiple neuronal oscillations across the cortex. Within the primary visual cortex (V1), large visual stimuli (gratings) can induce two gamma oscillations - slow (20-35 Hz) and fast (40-60 Hz), potentially due to two different interneuronal classes. However, wave like behaviour of these rhythms and their relationship is unknown. We showed large gratings to monkeys that simultaneously induced slow and fast gamma while recording from V1 using microelectrode arrays. Both slow and fast gamma were organized as travelling waves that were not locked to stimulus onset. Direction of wave propagation was significantly different but showed no correlation, even in concurrent waves. Slow gamma waves lasted for longer durations than fast gamma. Wave direction varied with stimulus orientation and spatial frequency. Thus, slow and fast gamma oscillations in V1 show unique spatial and temporal wave dynamics signifying that these gamma rhythms are generated by distinct neural circuits.