Intensity-Dependent Effects of 4-Week Transcranial Direct Current Stimulation on Motor Learning in Healthy Young Adults

Motor learning is essential for skill acquisition. Despite the potential of transcranial direct current stimulation (tDCS) to improve motor learning, the optimal stimulation parameters remain uncertain. This study investigated the acute and cumulative effects of varying anodal tDCS intensities on motor learning in healthy adults. This study was a single-blind randomized controlled trial. Forty-three healthy young adults (aged 18–25 years) were randomly assigned to 4 groups: sham-tDCS, 1 mA-tDCS, 2 mA-tDCS, and 3 mA-tDCS. The tDCS intervention comprised 10 sessions administered over 4 wk. The Serial Reaction Time Task was employed to evaluate motor learning at 4 timepoints: baseline, immediately after the first intervention, 1 day and 1 week after the end of all interventions. The calculation of absolute RT (block 6) minus absolute RT (block 5) was performed to assess selective motor sequence learning. No significant difference in motor learning was observed across groups (all p > 0.05) at T0 and T1. However, motor learning improved significantly in the 2 mA-tDCS group compared with the sham-tDCS group at T2 (p = 0.040) and T3 (p < 0.001). At T3, the 2 mA-tDCS group showed a superior performance relative to the 1 mA-tDCS (p = 0.002) and 3 mA-tDCS (p = 0.008) groups. Ten sessions of 2 mA tDCS significantly improved motor learning, and this effect persisted ≥ 1 week post-intervention. However, acute tDCS did not show a significant enhancement in motor learning.Clinical Trial Registration No: NCT07089069.