β-Bursts Reveal the Trial-to-Trial Dynamics of Movement Initiation and Cancellation

The neurophysiological basis of motor control is of substantial interest to basic researchers and clinicians alike. Motor processes are accompanied by prominent field potential changes in the beta-frequency band (15-29 Hz): in trial-averages, movement initiation is accompanied by beta-band desynchronization over sensorimotor areas, whereas movement cancellation is accompanied by beta -power increases over , (pre)frontal areas. However, averaging misrepresents the true nature of the beta-signal. Unaveraged beta-band activity is characterized by short-lasting, burst-like events, rather than by steady modulations. Therefore, averaging-based quantifications may miss important brain-behavior relationships. To investigate how beta-bursts relate to movement in male and female humans (N = 234), we investigated scalp-recorded beta-band activity during the stop-signal task, which operationalizes both movement initiation and cancellation. Both processes were indexed by systematic spatiotemporal changes in beta-burst rates. Before movement initiation, beta-bursting was prominent at bilateral sensorimotor sites. These burst-rates predicted reaction time (a relationship that was absent in trial-average data), suggesting that sensorimotor beta-bursting signifies an inhibited motor system, which has to be overcome to initiate movements. Indeed, during movement initiation, sensorimotor burst-rates steadily decreased, lateralizing just before movement execution. In contrast, successful movement cancellation was signified by increased phasic beta-bursting over fronto-central sites. Such beta-bursts were followed by short latency increases of bilateral sensorimotor beta-burst rates, suggesting that motor inhibition can be rapidly re-instantiated by frontal areas when movements have to be rapidly cancelled. Together, these findings suggest that beta-bursting is a fundamental signature of the motor system, used by both sensorimotor and frontal areas involved in the trial-by-trial control of behavior.