Abstract
This study was performed to investigate the possibility of non-invasive modulation of SEPs by the application of transcranial static magnetic field stimulation (tSMS) over the primary motor cortex (M1) and supplementary motor cortex (SMA), and to measure the strength of the NdFeB magnetic field by using a gaussmeter. An NdFeB magnet or a non-magnetic stainless steel cylinder (for sham stimulation) was settled on the scalp over M1 and SMA of 14 subjects for periods of 15 min. SEPs following right median nerve stimulation were recorded before and immediately after, 5 min after, and 10 min after tSMS from sites C3′ and F3. Amplitudes of the N33 component of SEPs at C3′ significantly decreased immediately after tSMS over M1 by up to 20%. However, tSMS over the SMA did not affect the amplitude of any of the SEP components. At a distance of 2–3 cm (rough depth of the cortex), magnetic field strength was in the range of 110–190 mT. Our results that tSMS over M1 can reduce the amplitude of SEPs are consistent with those of low-frequency repeated TMS and cathodal tDCS studies. Therefore, tSMS could be a useful tool for modulating cortical somatosensory processing.
Highlights
In this study, we assessed whether transcranial static magnetic field stimulation (tSMS) with other magnet positions can modulate the amplitude of Somatosensory evoked potentials (SEPs)
Previous studies reported that facilitatory rTMS14, TBS15, QPS16 and anodal transcranial direct current stimulation (tDCS) over M117 change the amplitude of the P25 and/or N33 component of SEPs at C3′.In our previous study, we demonstrated that tSMS over C3 changes the amplitude of the N20 component of SEPs at C3′; in that study, the NdFeB magnet seemed to cover S1 as well as M1, crossing over the central sulcus, and mainly or partly acted on S1
For the P25 component of SEPs recorded from C3′, two-way repeated measures analysis of variance (ANOVA) revealed a significant main effect of the stimulus site of tSMS (F2, 26 = 5.79, p = 0.008), but no significant main effect of time and the interaction between the stimulus site of tSMS and time was observed
Summary
We assessed whether tSMS with other magnet positions can modulate the amplitude of SEPs. The supplementary motor area (SMA) is thought to be a generator of SEPs (N30 from F3)[18,19] If these amplitudes of SEPs were affected by tSMS over SMA, it would demonstrate that tSMS is a beneficial technique for modulating the excitability of the sensorimotor and visual cortices, and of the SMA, which is the motor association cortex. The present study had two aims: to investigate the possibility of non-invasive modulation of SEPs by the application of tSMS over M1 and SMA in healthy humans, and to measure the strength of the NdFeB magnetic field using a gaussmeter
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