Transcranial static magnetic stimulation over the primary motor cortex alters sequential implicit motor learning.

Transcranial static magnetic stimulation (tSMS) is a recently introduced noninvasive brain stimulation technique that can modulate brain excitability. Here, we investigated a hypothesis that motor learning would be altered by tSMS applied to the primary motor cortex (M1). For motor task, we chose a serial reaction time task consisting of sequential trials and random trials in which the visual cue doesn't play out a repeating pattern of positions to evaluate an implicit motor learning, where the M1 is a key structure for skill acquisition and early consolidation. Forty-four healthy right-handed volunteers participated in the present study. TSMS was placed over the right M1 or dorsolateral prefrontal cortex (DLPFC). The control group received Sham stimulation over the right M1. Reaction times (RTs) of left hand were analyzed before (Pre session) and after (Post session) practice to examine online learning, and were also assessed 24 h later to examine offline learning (Cons session). The results showed that the RTs became faster in Post than Pre session regardless of the stimulation location. Interestingly, the RTs were significantly faster with the M1 stimulation than the DLPFC or Sham stimulation in Cons session. There was not significant difference in error rate among sessions or stimulation locations. These findings suggest that the modulation of the M1 using tSMS can enhance offline motor learning in an implicit task.

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