Repetitive Peripheral Magnetic Stimulation of Wrist Extensors Enhances Cortical Excitability and Motor Performance in Healthy Individuals

Abstract

Repetitive peripheral magnetic stimulation (rPMS) may improve motor function following central nervous system lesions, but the optimal parameters of rPMS to induce neural plasticity and mechanisms underlying its action remain unclear. We examined the effects of rPMS over wrist extensor muscles on neural plasticity and motor performance in 26 healthy volunteers. In separate experiments, the effects of rPMS on motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), direct motor response (M-wave), Hoffmann-reflex, and ballistic wrist extension movements were assessed before and after rPMS. First, to examine the effects of stimulus frequency, rPMS was applied at 50, 25, and 10 Hz by setting a fixed total number of stimuli. A significant increase in MEPs of wrist extensors was observed following 50 and 25 Hz rPMS, but not 10 Hz rPMS. Next, we examined the time required to induce plasticity by increasing the number of stimuli, and found that at least 15 min of 50 and 25 Hz rPMS was required. Based on these parameters, lasting effects were evaluated following 15 min of 50 or 25 Hz rPMS. A significant increase in MEP was observed up to 60 min following 50 and 25 Hz rPMS; similarly, an attenuation of SICI and enhancement of ICF were also observed. The maximal M-wave and Hoffmann-reflex did not change, suggesting that the increase in MEP was due to plastic changes at the motor cortex. This was accompanied by increasing force and electromyograms during wrist ballistic extension movements following 50 and 25 Hz rPMS. These findings suggest that 15 min of rPMS with 25 Hz or more induces an increase in cortical excitability of the relevant area rather than altering the excitability of spinal circuits, and has the potential to improve motor output.

Effects of Repetitive Peripheral Magnetic Stimulation through Hand Splint Materials on Induced Movement and Corticospinal Excitability in Healthy Participants

“…Previous studies have shown that rPMS activates the cerebral cortex (using recorded somatosensory evoked potentials) [ 26 , 27 , 28 ]; the front-parietal cerebral network (using positron emission tomography) [ 1 ]; and the sensorimotor cortex (using functional magnetic resonance imaging) [ 2 ]. In addition, other previous studies have shown that applying rPMS at 25 Hz with intensity above the motor threshold for 20 min facilitated corticospinal excitability of forearm muscles [ 2 , 4 ]. The rPMS settings used in our study were similar to those in the previous studies [ 2 , 4 ], and we showed that rPMS facilitated corticospinal excitability in L 0.…”

“…In addition, other previous studies have shown that applying rPMS at 25 Hz with intensity above the motor threshold for 20 min facilitated corticospinal excitability of forearm muscles [ 2 , 4 ]. The rPMS settings used in our study were similar to those in the previous studies [ 2 , 4 ], and we showed that rPMS facilitated corticospinal excitability in L 0. A previous systematic review of PES indicated that the stimulus intensity, especially when it is above the motor threshold, is an important modulator of corticospinal excitability [ 29 ].…”

“…It also induces activation of not only the sensorimotor cortex but also the front-parietal network, including premotor and parietal areas [ 1 , 2 ]. In addition, rPMS modulates the corticospinal excitability and intracortical circuits as well as enhances motor performance in healthy individuals [ 3 , 4 , 5 ]. Moreover, rPMS is a novel neurorehabilitation method for improving sensorimotor dysfunctions in stroke [ 1 , 6 , 7 , 8 , 9 , 10 ] and reducing lower back pain [ 11 , 12 ].…”

Checklist on the Quality of the Repetitive Peripheral Magnetic Stimulation (rPMS) Methods in Research: An International Delphi Study

“…Most commonly, the muscle contraction threshold or the movement threshold has been used. The former is determined by visual inspection or by palpation of a slight muscle contraction ( 9 , 25 , 34 , 35 ). The latter is obviously influenced by limb weight, inertia and position in relation to the gravity, resulting in a lower sensitivity and variability ( 14 , 34 – 36 ).…”

Body representation underlies response of proprioceptive acuity to repetitive peripheral magnetic stimulation

“…The direct relationship between rPMS and joint motor control remains less known; however, given the significance of neural mechanisms of motor function recovery, it is relevant to establish the effect of rPMS on response of proprioceptive acuity in healthy adults. Nito et al (2021) examined the effects of rPMS over wrist extensor muscles on neural plasticity and motor performance in healthy volunteers, in which significant increase in motor-evoked potentials (MEPs) was observed, but the maximal M-wave and Hoffmann-reflex did not change, suggesting the plastic changes at the motor cortex. Since rPMS could input proprioception inflow to CNS, and proprioception contributes to body representation, combining with the former hypothesis, we further hypothesized that proprioceptive acuity of wrist joint position sense might be influenced differently at different extension positions by rPMS.…”