Non-invasive modulation of somatosensory evoked potentials by the application of static magnetic fields over the primary and supplementary motor cortices

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.

Field Distribution of Transcranial Static Magnetic Stimulation in Realistic Human Head Model

“…Our characterization of the tSMS B-field was consistent with and extended previous measurements (3,23) by providing a complete 3D distribution of the field magnitude and gradient in air and in a computational model of the human head and brain. At distances up to approximately 4.7 cm from the base of the magnet, the B-field was > 40 mT, which is believed to be sufficient for physiological effects (33).…”

“…The magnet position was selected for the DLPFC, M1, and occipital cortex with reference to an atlas . The magnet position for SMC was selected with reference to the standard EEG electrode placement system . All targets were simulated for two distances of the magnet surface from the underlying scalp—0 mm and 5 mm—the latter representing the case when hair or hardware are interposed between the magnet and the scalp.…”

“…We characterized a permanent magnet typically used for tSMS (1)(2)(3)(4)6,28,29). The magnet is made of grade N52 NdFeB alloy and is cylindrical with diameter of 2 00 (5.08 cm) and height of 1 00 (2.54 cm) (Model # ND076-N52, Applied Magnets, Plano, TX, USA; see Fig.…”

Combination of Static Magnetic Fields and Peripheral Nerve Stimulation Can Alter Focal Cortical Excitability

“…Regarding the strength of the magnetic field, recent study reported that magnet used in this study was in range between 120 and 200 mT 2–3 cm from the surface of the magnet (Rivadulla et al, 2014; Kirimoto et al, 2016). Therefore, it seems that this range is enough to obtain biological effects.…”

“…The maximum energy density was 406 kJ/m3 (48–51 MGOe), with a nominal strength of 863 N (88 kg). The surface magnetic flux density was about 5340 G. At 2–3 cm from the magnet surface, magnetic field strength of this magnet on the cylinder axis is 120–200 mT (Rivadulla et al, 2014, Kirimoto et al, 2016). A nonmagnetic stainless-steel cylinder, of the same size, weight and appearance as the real magnet, was used for sham stimulation in the control group.…”