The Effect of Motor Imagery on Spinal Motor Neuron Excitability and Its Clinical Use in Physical Therapy

Abstract

We investigated the influence of the imagined muscle contraction strengths on spinal motor neuron excitability in healthy volunteers. F-wave was used for assessing spinal motor excitability. The F-waves during motor imagery (MI) under 10, 30, 50, 70, and 100% maximal voluntary contractions (MVCs) were compared. Furthermore, we investigated changes of the F-waves during motor imagery for 5min. Motor imagery under 10, 30, 50, 70, and 100% maximal voluntary contractions can increase spinal motor neuron excitability. However, the imagined muscle contraction strengths were not involved in changes of spinal motor neuron excitability. Additionally, spinal motor neuron excitability after 5min from onset of motor imagery returned to the rest level. Thus, in clinical use of motor imagery, slightly imagined muscle contraction strength is enough for facilitating spinal motor neuron excitability. Also, duration of motor imagery needs to be considered.

The Application of Motor Imagery to Neurorehabilitation

“…The imagined muscle contraction did not affect the change of the sympathetic nerve activity. This is very similar with the result of the spinal motor neuron excitability during MI at various imagined muscle contraction strengths [24][25][26]28]. If central command during MI affects the sympathetic nerve activity via the corticospinal pathway, the imagined muscle contraction strength may affect the sympathetic nerve activity.…”

“…The F/M amplitude ratio during MI under 10, 30, and 50% MI conditions was significantly greater than that at rest (10% MI vs. Rest, 50% MI vs. Rest, **p < 0.01; 30% MI vs. Rest, *p < 0.05) ( Tables 1-3). The F/M amplitude ratio during MI under 70% MI condition was tended to be increased than that at rest (p ≒ 0.082) ( Table 4) The relative values of the persistence, F/M amplitude ratio, and latency did not exhibit significant differences among all MI conditions ( Our previous works [24][25][26] suggested that MI of isometric thenar muscle activity at 10, 30, 50, and 70% MVC can facilitate the spinal motor neuron excitability. However, the imagined muscle contraction strength did not influence on change of the spinal motor neuron excitability.…”

“…Specifically, we adopted the 10, 30, 50, and 70% MVC for imagined muscle contraction strength. In this research, we assessed the spinal motor neuron excitability during MI by using the F-wave [24][25][26].…”

Motor Imagery for Neurorehabilitation: The F-Wave Study

“…In our previous studies, duration of MI was 1 min [23][24][25][26]. However, Driskell et al [45] indicated that 10-15 min may be appropriate for duration of MI training session.…”

“…Previously, we investigated the influence of MI of isometric thenar muscle activity on the excitability of spinal motor neurons [18,[23][24][25][26]. Previous results indicated that the MI of thenar muscle activity at 50% MVC can increase the excitability of spinal motor neurons.…”