Dual-hemisphere transcranial direct current stimulation over primary motor cortex enhances consolidation of a ballistic thumb movement

Transcranial direct current stimulation (tDCS) is a noninvasive technique that modulates motor performance and learning. Previous studies have shown that tDCS over the primary motor cortex (M1) can facilitate consolidation of various motor skills. However, the effect of tDCS on consolidation of newly learned ballistic movements remains unknown. The present study tested the hypothesis that tDCS over M1 enhances consolidation of ballistic thumb movements in healthy adults. Twenty-eight healthy subjects participated in an experiment with a single-blind, sham-controlled, between-group design. Fourteen subjects practiced a ballistic movement with their left thumb during dual-hemisphere tDCS. Subjects received 1 mA anodal tDCS over the contralateral M1 and 1 mA cathodal tDCS over the ipsilateral M1 for 25 min during the training session. The remaining 14 subjects underwent identical training sessions, except that dual-hemisphere tDCS was applied for only the first 15 s (sham group). All subjects performed the task again at 1 h and 24 h later. Primary measurements examined improvement in peak acceleration of the ballistic thumb movement at 1 h and 24 h after stimulation. Improved peak acceleration was significantly greater in the tDCS group (144.2 ± 15.1%) than in the sham group (98.7 ± 9.1%) (P < 0.05) at 24 h, but not 1 h, after stimulation. Thus, dual-hemisphere tDCS over M1 enhanced consolidation of ballistic thumb movement in healthy adults. Dual-hemisphere tDCS over M1 may be useful to improve elemental motor behaviors, such as ballistic movements, in patients with subcortical strokes.