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.
Highlights
motor evoked potential (MEP) To determine whether the frequency of Repetitive peripheral magnetic stimulation (rPMS) have the different effects on corticospinal excitability and spinal network excitability, we applied rPMS using different frequencies
MEPs In order to investigate the lasting effects of rPMS on MEPs, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF), we examined these parameters over a time course after rPMS was performed
These results suggest that 15 min of rPMS with 25 Hz or more may be an effective way to promote rehabilitation training by enhancing cortical excitability and motor outputs, in stroke patients or patients with neurodegenerative disorders
Summary
Peripheral nerve electrical stimulation is known to augment synaptic plasticity in motor cortex and spinal circuits in healthy individuals and in patients following stroke (Ridding et al, 2000; Kaelin-Lang et al, 2002; Khaslavskaia et al, 2002; McKay et al, 2002; Knash et al, 2003; Everaert et al, 2010; Mang et al, 2010; Chipchase et al, 2011a,b; Schabrun et al, 2012; Yamaguchi et al, 2012, 2013; Gallasch et al, 2015; Sasaki et al, 2017; Takahashi et al, 2018). Previous studies have shown that rPMS improves motor dysfunction following central nervous system (CNS) lesions (Struppler et al, 2003; Flamand et al, 2012; Beaulieu and Schneider, 2013; Flamand and Schneider, 2014); stimulus parameters such as frequency and intervention time in these reports are not constant, and plastic changes in cortical excitability have not been directly investigated
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