Transcranial static magnetic stimulation over the motor cortex can facilitate the contralateral cortical excitability in human

Yasuyuki Takamatsu,Tatsunori Watanabe,Ryota Shimomura,Yoshihiro Yukawa,Tatsuya Mima,Sumiya Shibata,Satoko Koganemaru,Masatoshi Minakuchi

doi:10.1038/s41598-021-84823-4

Abstract

Transcranial static magnetic stimulation (tSMS) has been focused as a new non-invasive brain stimulation, which can suppress the human cortical excitability just below the magnet. However, the non-regional effects of tSMS via brain network have been rarely studied so far. We investigated whether tSMS over the left primary motor cortex (M1) can facilitate the right M1 in healthy subjects, based on the hypothesis that the functional suppression of M1 can cause the paradoxical functional facilitation of the contralateral M1 via the reduction of interhemispheric inhibition (IHI) between the bilateral M1. This study was double-blind crossover trial. We measured the corticospinal excitability in both M1 and IHI from the left to right M1 by recording motor evoked potentials from first dorsal interosseous muscles using single-pulse and paired-pulse transcranial magnetic stimulation before and after the tSMS intervention for 30 min. We found that the corticospinal excitability of the left M1 decreased, while that of the right M1 increased after tSMS. Moreover, the evaluation of IHI revealed the reduced inhibition from the left to the right M1. Our findings provide new insights on the mechanistic understanding of neuromodulatory effects of tSMS in human.

Highlights

Transcranial static magnetic stimulation has been focused as a new non-invasive brain stimulation, which can suppress the human cortical excitability just below the magnet
There were no adverse events for all subjects during or after Transcranial static magnetic stimulation (tSMS) and transcranial magnetic stimulation (TMS) measurement procedure
We investigated the effect of tSMS over the left M1 on the cortical excitability of the right M1 and found that the direction of motor evoked potentials (MEPs) change was inverse for the left and right hands in real stimulation

Summary

Introduction

Transcranial static magnetic stimulation (tSMS) has been focused as a new non-invasive brain stimulation, which can suppress the human cortical excitability just below the magnet. Due to the predominance of inhibitory function in this interhemispheric connection (interhemispheric inhibition: IHI), it has been reported that the suppression of one brain region can cause the functional facilitation of the contralateral region, via the reduction of IHI from the suppressed site to the other s ide[1,2,3]. This phenomenon is called paradoxical functional facilitation (PFF)[4], which can be found in visual, attention and motor functions across experimental animal and human studies[5,6,7,8,9]. To investigate the remote effect of the focal brain modulation through neural network, we tested the motor excitability of the right M1 after tSMS intervention on the left M1, based on the hypotheses that the suppressions of M1 would produce the PFF and facilitate the motor function of the right M1 (Experiment 1) and that this remote effect is associated with the reduction of the IHI from the left to the right M1 (Experiment 2)

Methods

Results

Conclusion