[Abstract] The aim of the present study was to investigate in healthy humans the possibility of anon-invasive modulation of motor cortex excitability by the application of static magnetic fieldsthrough the scalp. Static magnetic fields were obtained by using cylindrical NdFeB magnets. Weperformed four sets of experiments. In Experiment 1, we recorded motor potentials evoked bysingle-pulse transcranial magnetic stimulation (TMS) of the motor cortex before and after 10minof transcranial static magnetic field stimulation (tSMS) in conscious subjects. We observed anaverage reduction of motor cortex excitability of up to 25%, as revealed by TMS, which lasted forseveralminutes after the end of tSMS, andwas dose dependent (intensity of the magnetic field) butnot polarity dependent. In Experiment 2, we confirmed the reduction of motor cortex excitabilityinduced by tSMS using a double-blind sham-controlled design. In Experiment 3, we investigatedthe duration of tSMS that was necessary to modulate motor cortex excitability. We found that10 min of tSMS (compared to 1min and 5 min) were necessary to induce significant effects. InExperiment 4, we used transcranial electric stimulation (TES) to establish that the tSMS-inducedreduction ofmotor cortex excitability was not due to corticospinal axon and/or spinal excitability,but specifically involved intracortical networks. These results suggest that tSMS using small staticmagnets may be a promising tool to modulate cerebral excitability in a non-invasive, painless,and reversible way.
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