Effects of EEG-guided transcranial alternating current stimulation (tACS) of the cerebellum on motor behavior and electrophysiological activity.

The cerebellum plays a key role in motor control, yet its oscillatory dynamics remain poorly understood due to anatomical and methodological constraints. Transcranial alternating current stimulation (tACS) has emerged as a promising tool to modulate cerebellar activity, particularly when tailored to individual neural oscillations. This study examined the effects of EEG-guided gamma-frequency cerebellar tACS-matched to each participant's individual gamma frequency (IGF)-on motor performance and neurophysiological markers in healthy adults. Forty-four male and female participants completed a visuomotor task while undergoing either real or sham tACS across two sessions. Critically, EEG activity was recorded before and immediately after the stimulation while participants performed the visuomotor task to assess electrophysiological changes in power spectrum density. Measures of corticospinal excitability and inhibition were collected via transcranial magnetic stimulation (TMS) protocols following each stimulation session. tACS at IGF enhanced motor precision during challenging task conditions and reduced corticospinal inhibition, without affecting corticospinal excitability. EEG analyses revealed IGF-dependent increases in theta-band power post-stimulation in motor regions, suggesting cross-frequency interactions. These findings highlight the potential of personalized cerebellar tACS to enhance motor performance and modulate inhibitory cortical dynamics, supporting its use as a precision neuromodulation tool in both research and clinical settings.