Frequency-band coupling in surface EEG reflects spiking activity in monkey V1 during passive fixation

Abstract

Although EEG is one of the most widely used tools to study brain activity in humans, its neurophysiological constituents are not well understood. We recently showed that during the presentation of movie stimuli, the multi unit activity (MUA) in V1 could be accurately modeled by using the EEG modulations in low frequency (2-4 Hz) phase and high frequency (>30 Hz) power. However, whether this relationship also holds for situations without direct visual stimulation remains unanswered. Therefore, we present data from simultaneous recordings of surface EEG and MUA in area V1 of one behaving monkey during a simple fixation task (trials consisted of a 9 second fixation period). In each trial, we first filtered the data into the delta (2-4Hz) and gamma (>30Hz) band, and found that changes in MUA were positively correlated to gamma power (R=0.12±0.03), and significantly tuned to the phase of the delta oscillation (rayliegh test, p<<0.001). Furthermore, we found that MUA responses were greatest when an increase in gamma power coincided with the negative-going (~ 0.8π) phase of the delta oscillation, suggesting that the strength of MUA in V1 is directly related to the precise interaction of low frequency phase and high frequency power (frequency-band coupling or FBC). These results resemble our earlier findings during the presentation of movie stimuli, and suggest that the relationship between FBC and MUA holds true in both stimulus and stimulus-free conditions