The Effects of Unihemispheric Concurrent Dual-Site Transcranial Direct Current Stimulation on Motor Sequence Learning in Healthy Individuals: A Randomized, Clinical Trial

Background: Unihemispheric concurrent dual-site anodal transcranial direct current stimulation (a-tDCSUHCDS) of the primary motor cortex (M1) and dorsolateral prefrontal cortex (DLPFC) are introduced as effective techniques on M1 corticospinal excitability enhancement and its after-effects. Objectives: The current study aimed at investigating the potential effects of multiple sessions of a-tDCSUHCDS of M1-DLPFC on motor skills learning in healthy individuals. Methods: The randomized, clinical trial was conducted on a total of 37 volunteers completed all sessions of the study and were randomly divided into two groups of a-tDCSUHCDS and sham stimulation by the block randomization method. The current study was performed from January to May 2017 in Iran. Participants attended daily 20-minute motor training sessions for three consecutive days, while they concurrently received a-tDCS. Motor skills were assessed before the intervention (day 1), immediately after the intervention (day 3), and one week after the completion of the intervention. Results: A total of 37 participants were included in the data analysis. Immediately after the completion of the intervention on day 3, mean skills in the experimental and control groups were 0.33 and 0.30, respectively. One week after the completion of the intervention, mean skills in the experimental and control groups were 0.36 and 0.29, respectively. The trend of motor learning considerably increased in the experimental (0.17; P < 0.001) and control (0.11; P < 0.001) groups. No significant difference was observed in motor learning immediately after the intervention between the groups (P = 0.23), while there was a significant difference in long-term offline learning between the groups (P = 0.04). Conclusions: Greater motor skills in the a-tDCSUHCDS group compared with the sham tDCS group at one-week retention indicated the robustness of the a-tDCSUHCDS effect.