Timing-Dependent Effects of Transcranial Direct Current Stimulation on Hand Motor Function in Healthy Individuals: A Randomized Controlled Study

The timing of transcranial direct current stimulation (tDCS) is essential for enhancing motor skill learning. Previously, tDCS, before or concurrently, with motor training was evaluated in healthy volunteers or elderly patients, but the optimal timing of stimulation has not been determined. In this study, we aimed to optimize the existing tDCS protocols by exploring the timing-dependent stimulation effects on finger movements in healthy individuals. We conducted a single-center, prospective, randomized controlled trial. The study participants (n = 39) were randomly assigned into three groups: tDCS concurrently with finger tapping training (CON), tDCS prior to finger tapping training (PRI), and SHAM-tDCS simultaneously with finger tapping training (SHAM). In all groups, the subjects participated in five 40-min training sessions for one week. Motor performance was measured before and after treatment using the finger-tapping task (FTT), the grooved pegboard test (GPT), and hand strength tests. tDCS treatment prior to finger tapping training significantly improved motor skill learning, as indicated by the GPT and hand strength measurements. In all groups, the treatment improved the FTT performance. Our results indicate that applying tDCS before training could be optimal for enhancing motor skill learning. Further research is required to confirm these findings.