Objective: Transcranial static magnetic field stimulation (tSMS) has recently been demonstrated to modulate cortical excitability and perceptual functions in humans, however, the effect of tSMS on motor behavior is still unknown. We investigated whether tSMS over the primary motor cortex (M1) alters voluntary ballistic force control. Materials and Methods: Twenty healthy participants performed ballistic pinch contractions in both hands alternatively at a predetermined submaximal force level and without visual feedback, before, during and after tSMS and sham interventions. A compact magnet for tSMS and a stainless steel cylinder for sham stimulation were positioned over the either right or left M1 for 15 min. Results: The absolute error to the target force level was significantly larger for the tSMS-intervened hand than for the sham-intervened hands during and after intervention (p < 0.05, respectively). Compared with the preintervention session, the absolute error increased in the tSMS-intervened hand during and after intervention (p < 0.05, respectively), but not in the sham-intervened hand. Conclusions: tSMS over M1 can impair the accuracy of submaximal ballistic pinch force control. This suggests that tSMS is strong enough to alter motor behavior in humans.
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