Dissociation between cortical and spinal excitability of the antagonist muscle during combined motor imagery and action observation

Toshiyuki Aoyama,Fuminari Kaneko,Yutaka Kohno,Yukari Ohashi

doi:10.1038/s41598-019-49456-8

Toshiyuki Aoyama, Fuminari Kaneko + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-49456-8

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Abstract

Inhibitory neural control of antagonist muscle is one of the fundamental neural mechanism of coordinated human limb movement. Previous studies have revealed that motor execution (ME) and motor imagery (MI) share many common neural substrates; however, whether inhibitory neural activity occurs during MI remains unknown. In addition, recent studies have demonstrated that a combined MI and action observation (MI + AO) produces strong neurophysiological changes compared with MI or AO alone. Therefore, we investigated inhibitory changes in cortical and spinal excitability of the antagonist muscle during MI + AO and ME. Single-pulse transcranial magnetic stimulation (TMS) experiments revealed that corticospinal excitability of the antagonist muscle was decreased during MI + AO. Conversely, F-wave experiments showed that F-wave persistence of the antagonist muscle increased. Paired-pulse TMS experiment also demonstrated that short-interval intracortical inhibition (SICI) did not contribute to this inhibition. Therefore, cortical mediated inhibition, except for SICI, may be related to this inhibition. Conversely, such clear inhibition of the antagonist muscle was not observed during ME, presumably owing to the effects of muscle contraction to decelerate the movements and/or sensory input accompanying the joint movements. These findings provide important insights into the neurophysiological differences between MI + AO and ME.

Highlights

Motor imagery (MI) is defined as the mental simulation of a given movement that is internally reproduced within brain without any muscular output[1,2]
Considering such neurophysiological similarities occurring during motor imagery (MI) and before movement onset in the agonist muscle, we hypothesized that corticospinal excitability of the antagonist muscles would be suppressed during MI
These results indicated that cortical-mediated inhibition, except short-interval intracortical inhibition (SICI), may be related to inhibitory changes in the corticospinal excitability of the antagonist muscle during MI + action observation (AO)

Summary

Introduction

Motor imagery (MI) is defined as the mental simulation of a given movement that is internally reproduced within brain without any muscular output[1,2]. MEP amplitude obtained from the agonist muscle increases before the movement onset[10] Since this corticospinal excitability change is not accompanied by an increase in agonist EMG activity, as well as during MI, the neurophysiological changes during MI and before movement onset are similar. Taking into account the potent effect of MI on neurophysiological changes during AO, we assumed that the corticospinal excitability of the antagonist muscle is suppressed by MI + AO, as it was observed before the onset of ME. We assume that there are clear differences in corticospinal and spinal excitability changes between during ME and MI + AO Taking this into account, the secondary aim of the present study was to examine the neurophysiological similarities and differences between ME and MI + AO

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