Cerebellar Transcranial Alternating Current Stimulation: Frequency-Specific Modulation of Human Gait.

Coordinated locomotion depends on rhythmic neural interactions, with the cerebellum contributing to movement timing and scaling. However, how cerebellar oscillatory dynamics influence human gait remains unclear, despite its relevance for motor learning and rehabilitation. We hypothesized two frequency-dependent effects: (i) gait-matched cerebellar transcranial alternating current stimulation (c-tACS) would produce stronger phase alignment than sham and selectively affect temporal rather than spatial gait parameters; and (ii) higher-frequency stimulation would preferentially modulate spatial gait parameters without consistent phase alignment with the ongoing locomotor rhythm. To test this, fifteen healthy adults received randomized bilateral c-tACS at their individual gait-cycle frequency (iGCF), iGCF ± 10% offsets, individual step frequency (iSF), a harmonic in alpha range (iGCF×10), 50 Hz (gamma), and sham. Head-mounted accelerometry recorded kinematics of continuous walking and a stop-and-go task. Phase synchrony between stimulation and gait periodicity was quantified using the debiased phase-locking value (dPLV). 50 Hz c-tACS increased gait velocity and stride length without altering cadence or stride time, indicating selective modulation of spatial gait parameters. In contrast, gait-matched stimulation (iGCF, iSF) produced strong stimulation-gait phase alignment but did not enhance temporal gait parameters beyond sham, arguing against entrainment-specific behavioral effects. dPLV declined with iGCF ± 10% during continuous walking, whereas a transient increase at iGCF-10% during stop-and-go was not specific to active stimulation. These findings support frequency-dependent effects of c-tACS on locomotion and refine the mechanistic understanding of how rhythmic cerebellar stimulation interacts with gait control, with potential implications for targeted neuromodulation.