Investigating Impact of Resting-state tACS on Motor Skill Learning

Jinyue Lin, Hiroyuki Hamada, Tsubasa Kawasaki, Ken Kikuchi, Qi An  and Atsushi Yamashita

Transcranial alternating current stimulation (tACS), a non-invasive method of modulating brain oscillatory activity, has garnered increasing attention in neuromodulation. Previous studies have suggested that tACS may enhance cognitive functions and potentially benefit motor skill learning, though effective protocols remain unestablished. In particular, mechanisms underlying its effects of tACS on motor learning remain unclear. Our previous research indicated that increased alpha-band activity in the prefrontal cortex, specifically around the AFz electrode site, during the resting state is positively correlated with motor learning performance. Therefore, the present study aims to investigate whether applying tACS over the AFz region during rest can enhance the rate and retention of subsequent motor skill learning. A single-blind design and a ball-rotation task were used. 8 healthy participants were randomly assigned to a tACS group or a sham group. A high-definition electrode montage was used, with AFz as the central site and four symmetric return electrodes. Participants received 10 minutes of 10 Hz tACS at 1 mA, or sham stimulation, during the resting state. The experimental procedure consisted of a pre-test, stimulation, motor skill learning task, post-test, and a retention test. During the pre-test, participants performed baseline ball-rotation trials in both clockwise (CW) and counterclockwise (CCW) directions. After the stimulation, participants engaged in 25 CW-direction training trials, each lasting 1 minute. A post-test assessed CW and CCW performance, followed by a retention test 30 minutes later. The task was confirmed to induce motor learning, as both CW and CCW performance significantly improved from pre-test to post-test (p < 0.01). To assess tACS effects on the learning process, linear slopes were derived from the 25 training trials and compared between groups. Although no significant group difference was found (p = 0.32), a moderate-to-large effect size was observed (Cohen’s d = 0.78, 95% CI [-0.66, 2.22]), which may indicate a trend toward enhanced learning speed in the tACS condition. Retention performance declined significantly in both tACS and sham groups (p < 0.05), with no significant group difference observed. A similar decline was noted in the untrained CCW direction, suggesting the reduction may reflect general fatigue or time-dependent decay rather than a stimulation-specific modulation. These preliminary findings suggest that resting-state alpha tACS may facilitate motor skill learning speed, though further studies with larger samples are warranted to confirm its efficacy.