Movement-related coupling of human subthalamic nucleus spikes to cortical gamma.
People with Parkinson’s can find it difficult to move. To understand more about how movement is controlled by the brain, we studied nerve cell activity recorded in two brain regions of people doing hand grips. We discovered that the relative timing of nerve cell activity in the two regions carried information about the start of gripping, suggesting that changes in timing may help to control movements.
Cortico-basal ganglia interactions continuously shape the way we move. Ideas about how this circuit works are based largely on models those consider only firing rate as the mechanism of information transfer. A distinct feature of neural activity accompanying movement, however, is increased motor cortical and basal ganglia gamma synchrony. To investigate the relationship between neuronal firing in the basal ganglia and cortical gamma activity during movement, we analysed human ECoG and subthalamic nucleus (STN) unit activity during hand gripping. We found that fast reaction times were preceded by enhanced STN spike-to-cortical gamma phase coupling, indicating a role in motor preparation. Importantly, increased gamma phase coupling occurred independent of changes in mean STN firing rates, and the relative timing of STN spikes was offset by half a gamma cycle for ipsilateral vs. contralateral movements, indicating that relative spike timing is as relevant as firing rate for understanding cortico-basal ganglia information transfer.