Beta transcranial alternating current stimulation over the dorsal premotor area impairs response initiation but not inhibition in humans.

BACKGROUND: Response initiation and inhibition are core components of movement control, supported by a distributed frontal network including the dorsal premotor cortex (PMd) and inferior frontal gyrus (IFG). Converging evidence suggests that neural oscillations, particularly in the β- and γ bands, contribute to both response initiation and inhibitory control. Transcranial alternating current stimulation (tACS) enables non-invasive, frequency-specific modulation of cortical oscillations, offering a tool to causally probe these mechanisms. This study investigated whether β- and γ-tACS applied over PMd or IFG affect response initiation and inhibition in healthy participants. MATERIALS AND METHODS: Twenty healthy right-handed participants performed a Stop Signal Task (SST) during online β (20 Hz) and γ (70 Hz) tACS applied bilaterally, over either the PMd or IFG, in randomised, separate sessions. Behavioural measures of response initiation included accuracy, reaction times (RTs) and RT variability. Response inhibition was measured using the probability of responding on Stop trials (p[R]) and stop-signal reaction time (SSRT). RESULTS: β-tACS, but not γ-tACS, over the PMd but not over the IFG, significantly reduced response accuracy, suggesting a disruption of response initiation processes. For response inhibition, neither β- nor γ-tACS over IFG or PMd significantly modulated p[R] or SSRT. CONCLUSIONS: PMd β-tACS selectively deteriorated response initiation in healthy participants. This finding implies that β-oscillations would play a key physiological role in response initiation. SIGNIFICANCE: Applying β-tACS over the PMd selectively deteriorated response initiation, but not inhibition, in healthy humans.