Phase-amplitude coupling between θ and γ oscillations during nociception in rat electroencephalography.

In electroencephalography (EEG) study, gamma oscillations were reported to participate in pain processing; theta oscillations were also involved in pain processing. Moreover, theta always modulated gamma activity by phase-amplitude coupling in event-related oscillations. Whether theta modulate gamma by phase-amplitude coupling in pain processing is of interest. In the present study, using EEG of rats after laser nociceptive stimulation, we investigated gamma activity and phase-amplitude coupling between theta and gamma. It was found that induced gamma power increased starting 200 ms after nociceptive stimulation onset. Moreover, significant coupling between theta phase and gamma amplitude was found over frontal and parietal region after nociceptive stimulation. Our results for the first time suggest that coupling between theta and gamma is involved in nociception processing.