Objective: To investigate the potential of transcranial static magnetic field stimulation (tSMS) for reducing corticospinal excitability when delivered to the primary motor cortex (M1) or to the supplementary motor area (SMA).

Background: Hyperkinetic movement disorders may be treated non-pharmacologically by decreasing corticospinal excitability with non-invasive brain stimulation (NIBS). tSMS is a new inhibitory NIBS technique, whose portability and easiness of use make it attractive for home-based long-term treatments. Both M1 and SMA are promising cortical targets.

Method: We performed two open studies testing the effects on corticospinal excitability of tSMS delivered either to M1 or SMA. Experiment 1: We recruited 40 right-handed healthy subjects (22 females; mean age: 30.6±7.7 years) who underwent one 30-min session of tSMS applied either over the right or left M1. We monitored corticospinal excitability by delivering TMS over the targeted M1 recording 30 motor evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI) muscle before and after (at 0, 15 and 30 minutes) tSMS. Experiment 2: We recruited 20 right-handed healthy subjects (5 females; mean age: 30.0 ± 6.7 years) who underwent two 30-min sessions (at least one week apart) of tSMS applied over SMA. We again monitored corticospinal excitability by delivering TMS over M1, recording 30 MEPs from either the left or right FDI in each session before and after (at 0, 15 and 30 minutes) tSMS. All analyses were performed using Bayesian statistics.

Results: We found a moderate evidence for a reduction of MEP amplitude after 30 minutes of tSMS over M1 (repeated measures [RM] ANOVA, BF_incl=5.42). Similarly, we found a moderate evidence for a reduction of MEP amplitude after 30 minutes of tSMS over SMA (RM ANOVA, BF_incl=5.61).

Conclusion: tSMS applied over either M1 or SMA may reduce corticospinal excitability. These findings, if confirmed with double-blind, placebo-controlled experiments, suggest that both cortical areas could be potential targets for future therapeutic applications of tSMS in movement disorders.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/reducing-corticospinal-excitability-with-transcranial-static-magnetic-field-stimulation/