Somatosensory evoked potentials and high-frequency oscillations after transcranial static magnetic stimulation over the primary somatosensory cortex

Transcranial static magnetic field stimulation (tSMS) is a non-invasive brain stimulation technique known to reduce cortical excitability. Although its effectiveness has been demonstrated in various cortical regions, it remains unclear whether somatosensory processing is influenced by this stimulation. The purpose of this study was to investigate whether tSMS over the primary somatosensory cortex (S1) modulates somatosensory evoked potentials (SEPs) and high-frequency oscillations superimposed on them (somatosensory HFOs). In a randomized crossover study, twenty healthy young adults received tSMS or sham stimulation over the left S1 (corresponding to C3 of the international 10-20 system) for 20 min. SEPs were recorded in response to right median nerve stimulation before, immediately after, and 20 min after stimulation. Somatosensory HFOs were extracted by applying a 400-800 Hz band-pass filter to SEP waveforms and separated into early and late components relative to the N20 peak latency. TSMS over the left S1 significantly reduced the amplitude of early HFOs 20 min after stimulation, whereas late HFOs remained unchanged. No effects of tSMS were observed on the N20 component of standard SEPs, which reflects neural activity in area 3b of the S1. Early and late HFOs are thought to reflect the action potentials of thalamocortical fibers and the activity of GABAergic interneurons, respectively. These findings therefore suggest that tSMS over the S1 selectively attenuates thalamocortical input while exerting no effect on GABAergic interneuron activity.