Phase-Specific Dual-Site Beta Transcranial Alternating Current Stimulation Differentially Influences Functional Connectivity Associated With Motor Inhibition Performance.

Inhibitory control relies on coordinated beta-band activity within a fronto-basal ganglia network, which implements inhibition via downstream effects on (pre)motor areas. However, the causal role of beta synchrony in motor inhibition remains unclear. In this study, we employed dual-site transcranial alternating current stimulation (tACS) targeting the right inferior frontal gyrus (rIFG) and left primary motor cortex (lM1) to directly manipulate phase relationships in the beta band and assess their effects on both functional connectivity and motor inhibition. Fifty-two healthy participants received in-phase, anti-phase, and sham stimulation while performing a stop-signal task. Connectivity between rIFG and lM1 increased following in-phase stimulation and decreased after anti-phase stimulation. No significant group-level effects on stop-signal task performance were observed. Exploratory Δ-Δ correlations indicated that individuals with larger connectivity increases during in-phase stimulation tended to show greater improvements in inhibitory performance, whereas greater connectivity decreases during anti-phase stimulation were associated with faster go responses. Crucially, ANCOVA analyses revealed significant stimulation-dependent changes in the slope of the connectivity-behavior relationship, demonstrating that tACS altered how beta synchrony predicted inhibitory and motor performance despite unchanged mean behavior. These findings suggest that dual-site beta-tACS can bidirectionally modulate rIFG-M1 connectivity in a phase-dependent manner and selectively alter how beta synchrony predicts stopping and motor execution. This mechanistic insight may inform future research exploring dual-site beta-tACS as a tool to probe or potentially normalize inhibitory network dynamics in disorders characterized by impaired inhibition.