Regulation of Motor Representation by Phase-Amplitude Coupling in the Sensorimotor Cortex

High-gamma amplitude (80-150 Hz) represents motor information, such as movement types, on the sensorimotor cortex. In several cortical areas, high-gamma amplitudes are coupled with low-frequency phases, e. g., alpha and theta (phase-amplitude coupling, PAC). However, such coupling has not been studied in the sensorimotor cortex; thus, its potential functional role has yet to be explored. We investigated PAC of high-gamma amplitude in the sensorimotor cortex during waiting for and the execution of movements using electrocorticographic (ECoG) recordings in humans. ECoG signals were recorded from the sensorimotor cortices of 4 epilepsy patients while they performed three different hand movements. A subset of electrodes showed high-gamma activity selective to movement type around the timing of motor execution, while the same electrodes showed nonselective high-gamma activity during the waiting period (>2 s before execution). Cross frequency coupling analysis revealed that the high-gamma amplitude during waiting was strongly coupled with the alpha phase (10-14 Hz) at the electrodes with movement-selective high-gamma amplitudes during execution. This coupling constituted the high-gamma amplitude peaking around the trough of the alpha oscillation, and its strength and phase were not predictive of movement type. As the coupling attenuated toward the timing of motor execution, the high-gamma amplitude appeared to be released from the alpha phase to build a motor representation with phase-independent activity. Our results suggest that PAC modulates motor representation in the sensorimotor cortex by holding and releasing high-gamma activity in movement-selective cortical regions.