tACS induces state-dependent shifts in inhibitory phase preference consistent with phase precession

Phase-dependent modulation of motor inhibition suggests that oscillatory timing plays a key role in inhibitory control. Here we show that rhythmic brain stimulation can selectively alter this timing in a manner consistent with phase precession. Participants performed an anticipatory stop-signal task while receiving 20 Hz transcranial alternating current stimulation (tACS) over the pre-supplementary motor area, with stop signals presented at defined phases of the stimulation waveform. An additional control experiment with no tACS was conducted, in which the stop signal phase was derived post-hoc from the ongoing EEG. In both tACS and control sessions, stopping efficacy varied sinusoidally with beta phase, confirming that inhibitory control is intrinsically phase-dependent. During tACS, however, the phase associated with the strongest inhibition advanced progressively across the session by about 180{degrees}, and this effect was specific to failed-stop trials. No comparable shift occurred without stimulation. These findings indicate that rhythmic drive can bias the temporal phase at which inhibition is most effective when the brain is in an error-prone state, revealing a state-dependent, precession-like reorganization of inhibitory timing. We propose that tACS interacts with error-related plasticity to promote gradual phase advancement, placing the system within spike-timing-dependent learning windows, whereas intrinsic fluctuations alone appear insufficient to facilitate cumulative precession. More broadly, these results suggest that phase precession may represent a general coding principle extending beyond hippocampal circuits, enabling the motor system to adaptively adjust inhibitory control through oscillatory timing mechanisms. HighlightsO_LIBeta tACS over preSMA induces shifts in phase preference during motor inhibition C_LIO_LIPrecession-like phase shifts emerge selectively during failed but not successful stops C_LIO_LIPhase precession was absent in a control experiment without tACS C_LIO_LItACS might provide a method to probe phase precession mechanisms in cognition C_LI