Gamma-cycle duration predicts instantaneous amplitude, spike rate and synchrony in macaque V1.

Communication among visual cortical areas depends on gamma oscillations. Respective gamma cycles vary substantially in amplitude and duration, yet it is unclear how those fundamental parameters relate to each other and to spiking activity. We recorded local-field-potentials (LFPs) and spiking activity from awake macaque area V1 and detected amplitude, duration and spiking activity per gamma cycle. Longer durations predicted larger amplitudes and stronger spike synchrony, yet lower spike rates. These findings suggest that spontaneous gamma-variability reflects inhibitory mechanisms that reduce spike rates, increase synchronization, and prolong the cycle duration. The classical LFP power-spectrum, estimated on longer time scales, was most strongly predicted from how often certain gamma-cycle durations occurred, rather than by their associated instantaneous amplitudes.