To investigate whether beta oscillations are causally related to motor inhibition thirty-six participants underwent two concurrent transcranial alternating current stimulation (tACS) and electroencephalography (EEG) sessions during which either beta (20Hz) or gamma (70Hz) stimulation was applied while participants performed a stop-signal task. In addition, we acquired magnetic resonance images to simulate the electric field during tACS.
20Hz stimulation targeted at the pre-supplementary motor area enhanced inhibition and increased beta oscillatory power around the time of the stop-signal in trials directly following stimulation. The increase in inhibition on stop trials followed a dose-response relationship with the strength of the individually simulated electric field. Computational modelling revealed that 20Hz and 70Hz stimulation had opposite effects on the braking process. These results highlight that the effects of tACS are state-dependent, and demonstrate that fronto-central beta activity is causally related to successful motor inhibition, supporting its use as a functional biomarker.