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

The present study aimed to investigate the effects of different intensities of tDCS-specifically 1 mA, 2 mA, and 3 mA-on motor learning in healthy adults. Both the acute effects following a single tDCS session and the cumulative effects after a 4-week intervention (10 sessions) were evaluated. Additionally, the study aimed to determine whether improvements in motor learning induced by 4 weeks of repeated tDCS would be sustained one week after completion of the intervention. We hypothesized that anodal tDCS at 2 mA would produce the most substantial improvement in motor sequence learning, both following a single session and after a 4-week intervention, compared to 1 mA, 3 mA, and sham stimulation. Furthermore, we expected that the motor learning gains observed in the 2 mA group would be sustained one week post-intervention, indicating the persistence of tDCS-induced effects. In contrast, we anticipated minimal improvement in the 1 mA group due to insufficient stimulation intensity, and no additional or even reduced benefits in the 3 mA group compared to the 2 mA group.