Motor Cortical Gamma Oscillations: What Have We Learnt and Where Are We Headed?

An increase in oscillatory activity in the -frequency band (approximately 50-100 Hz) has long been noted during human movement. However, its functional role has been difficult to elucidate. The advent of novel techniques, particularly transcranial alternating current stimulation (tACS), has dramatically increased our ability to study oscillations. Here, we review our current understanding of the role of oscillations in the human motor cortex, with reference to activity outside the motor system, and evidence from animal models. Evidence for the neurophysiological basis of human oscillations is beginning to emerge. Multimodal studies, essential given the necessarily indirect measurements acquired in humans, are beginning to provide convergent evidence for the role of oscillations in movement, and their relationship to plasticity. Human motor cortical oscillations appear to play a key role in movement, and relate to learning. However, there are still major questions to be answered about their physiological basis and precise role in human plasticity. It is to be hoped that future research will take advantage of recent technical advances and the physiological basis and functional significance of this intriguing and important brain rhythm will be fully elucidated.