Frequency-Dependent Effects of Transcranial Alternating Current Stimulation on Cerebro-Cerebellar Connectivity and...

The cerebellum is critical for sensorimotor performance, and transcranial alternating current stimulation (tACS) is a promising modulatory tool. To address the unclear frequency-specific effects of tACS on the cerebro-cerebellar network and sensorimotor performance, this study investigated how low- and high-frequency stimulation differentially modulate effective connectivity and sensorimotor performance. In this single-blind, sham-controlled, within-participant study, we first used magnetic resonance imaging (MRI)-based computational modeling to determine the optimal current intensity for a fixed F6-O2 cerebellar montage for each of the 22 participants. Then, participants completed three experimental sessions, receiving 20 min of 10 Hz, 70 Hz, or sham tACS at this optimized intensity. We assessed the after-effects on cerebro-cerebellar effective connectivity based on electroencephalogram (EEG) and performance on a sensorimotor performance task. The computational modeling indicated that a 2.0-mA current was optimal for the F6-O2 montage to target the cerebellum. The subsequent human experiments revealed opposing, frequency-specific effects on connectivity: 10-Hz stimulation broadly induced increases (Cohen's d = 0.19 to 0.33), whereas 70-Hz stimulation predominantly induced decreases (Cohen's d = -0.10 to -0.29). Despite these opposite neural effects, both frequencies similarly improved sensorimotor performance by reducing errors compared to sham (Cohen's d = -0.16 to -0.26). Our findings demonstrate that while low- and high-frequency cerebellar tACS exert opposite effects on network connectivity, both can similarly enhance sensorimotor performance. This suggests that distinct neural pathways can be engaged to support improvements in motor learning.