Frequency-Specific tACS Differentially Modulates Cortical Oscillations and Motor Performance

Transcranial alternating current stimulation (tACS) is a non-invasive neuromodulation technique with potential applications in motor rehabilitation, yet its concurrent effects on brain activity remain poorly understood due to the large stimulation artifacts in electroencephalography (EEG) recordings. In this study, we implemented a novel artifact removal algorithm, combining empirical wavelet transform and blind source separation, to remove the artifacts and investigate the effects of 20Hz and 70Hz tACS on cortical oscillations and motor task performance. To this end, fifteen healthy young adults received tACS at 20Hz, 70Hz, or sham as control over the contralateral motor cortex region while performing a handgrip motor task. We assessed pre-movement Mu/Beta spectral power, event-related desynchronization (ERD), and behavioural metrics (reaction time and grip force rise time) across both stimulation and post-stimulation periods. Results showed that 20Hz tACS increased pre-movement Mu/Beta power, enhanced ERD amplitude, and prolonged grip force rise time, whereas 70Hz tACS decreased Mu/Beta power and ERD amplitude, facilitating faster force generation. Both effects remained statistically significant up to 15 minutes post-stimulation. To our knowledge, this is the first study to characterize tACS-induced modulation of movement-related ERD using artifact-suppressed EEG. These findings demonstrate that frequency-specific entrainment of cortical oscillations influences motor output and support the development of individualized, closed-loop neurorehabilitation systems in the future.