Effect of Transcranial Static Magnetic Field Stimulation Over the Sensorimotor Cortex on Somatosensory Evoked Potentials in Humans

BACKGROUND The motor cortex in the human brain can be modulated by the application of transcranial static magnetic field stimulation (tSMS) through the scalp. However, the effect of tSMS on the excitability of the primary somatosensory cortex (S1) in humans has never been examined. OBJECTIVE This study was performed to investigate the possibility of non-invasive modulation of S1 excitability by the application of tSMS in healthy humans. METHODS tSMS and sham stimulation over the sensorimotor cortex were applied to 10 subjects for periods of 10 and 15 min. Somatosensory evoked potentials (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 of the international 10-20 system of electrode placement. In another session, SEPs were recorded from 6 of the 10 subjects every 3 min during 15 min of tSMS. RESULTS Amplitudes of the N20 component of SEPs at C3' significantly decreased immediately after 10 and 15 min of tSMS by up to 20%, returning to baseline by 10 min after intervention. tSMS applied while recording SEPs every 3 min and sham stimulation had no effect on SEP. CONCLUSIONS tSMS is able to modulate cortical somatosensory processing in humans, and thus might be a useful tool for inducing plasticity in cortical somatosensory processing. Lack of change in the amplitude of SEPs with tSMS implies that use of peripheral nerve stimulation to cause SEPs antagonizes alteration of the function of membrane ion channels during exposure to static magnetic fields.

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