Transcranial static magnetic stimulation modulates sensory interhemispheric inhibition as revealed by somatosensory evoked potentials and high-frequency oscillations.

Transcranial static magnetic stimulation (tSMS) is a non-invasive neuromodulation technique that reduces cortical excitability. Although tSMS has been reported to attenuate interhemispheric inhibition (IHI) within the motor cortex, its effects on IHI within the primary somatosensory cortex (S1) remain unclear. The purpose of this study was to determine whether tSMS over the S1 modulates somatosensory IHI using a paired somatosensory evoked potentials (pSEPs) paradigm. In a randomized crossover design, twenty-five healthy young adults received either tSMS or sham stimulation over the right S1 (C4 in the international 10-20 system) for 20 min. SEPs were elicited by a test stimulus delivered to the right median nerve, preceded by a conditioning stimulus (CS) delivered to the left median nerve at an interstimulus interval of 10 ms. Recordings were obtained before, immediately after, and 20 min after stimulation. In addition to the N20 and P27 SEP components, high-frequency oscillations (HFOs) were extracted and classified into early (eHFOs) and late (lHFOs) components relative to the N20 peak latency. TSMS over the right S1 significantly reduced CS-induced suppression of lHFOs in the left S1 immediately after stimulation, whereas eHFOs and N20/P27 components remained unchanged. Given that N20/P27 components, eHFOs, and lHFOs are thought to reflect activity in Brodmann area 3b of the S1, thalamocortical input, and GABAergic interneuron activity, respectively, these findings are consistent with the possibility that tSMS modulates transcallosal interactions involving intracortical inhibitory processing within the somatosensory system.