REPETITIVE PERIPHERAL MAGNETIC STIMULATION ENHANCES CONTRALATERAL CORTICOSPINAL EXCITABILITY VIA REDUCTION OF INTERHEMISPHERIC INHIBITION IN HEALTHY HUMANS

Repetitive peripheral magnetic stimulation (rPMS) is an emerging tool for modulating cortical excitability, but its influence on interhemispheric balance remains unclear. This study investigated the effects of rPMS on corticospinal excitability, exploring whether interhemispheric inhibition (IHI) contributes to this enhancement. Twenty-one healthy adults received rPMS (25 Hz, 2 s ON/OFF, 1.5 × motor threshold) to the right hand. The rPMS consisted of six sessions for a total of 30 minutes (5 min per session), and motor evoked potentials (MEPs) of the right first dorsal interosseous (FDI) muscle elicited by transcranial magnetic stimulation were assessed before (T0), between (T5, T10, T15, T20, T25), and after the sessions (T30). IHI was evaluated at T0, T15, and T30 using a paired-pulse TMS (10 ms interval) with conditioning stimulation to the right primary motor cortex (M1) and test stimulation to the left M1. MEPs and IHI of the left FDI were also assessed using the same protocol. MEPs of the right FDI significantly increased at T15 compared to T0, and then further increased at T30. Concurrently, IHI significantly decreased at T15 and further decreased at T30. Notably, the reduction in IHI was correlated with the increase in MEPs at T30. In contrast, no significant changes were observed in either the MEPs or IHI of the left FDI. These findings suggest that rPMS induces a progressive increase in contralateral corticospinal excitability, characterized by a concurrent reduction in IHI. Our results highlight the potential of rPMS as a tool for modulating interhemispheric balance.