Muscle-Specific Modulation of Spinal Reflexes in Lower-Limb Muscles during Action Observation with and without Motor Imagery of Walking.

Kaneko Kaneko,Nakazawa Nakazawa,Masugi Masugi,Yokoyama Yokoyama,Usuda Usuda

doi:10.3390/brainsci9120333

Abstract

Action observation (AO) and motor imagery (MI) are useful techniques in neurorehabilitation. Previous studies have reported that AO and MI facilitate corticospinal excitability only in those muscles that are active when actually performing the observed or imagined movements. However, it remained unclear whether spinal reflexes modulate multiple muscles simultaneously. The present study focused on AO and MI of walking and aimed to clarify their effects on spinal reflexes in lower-limb muscles that are recruited during actual walking. Ten healthy males participated in the present study. Spinal reflex parameters evoked by transcutaneous spinal cord stimulation were measured from five lower-limb muscles during rest, AO, and AO combined with MI (AO + MI) conditions. Our results showed that spinal reflexes were increased in the tibialis anterior and biceps femoris muscles during AO and in the tibialis anterior, soleus, and medial gastrocnemius muscles during AO + MI, compared with resting condition. Spinal reflex parameters in the vastus medialis muscle were unchanged. These results indicate the muscle-specific modulations of spinal reflexes during AO and AO + MI. These findings reveal the underlying neural activities induced by AO, MI, and their combined processes.

Highlights

Action observation (AO) and motor imagery (MI) are useful rehabilitation techniques for patients with neurological disorders
Fadiga et al [7,8] reported that both AO and MI facilitate the excitability of corticospinal tracts which can be assessed through motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) of the primary motor cortex
Our studies showed that AO + MI of walking increased both MEPs in the tibialis anterior (TA) and soleus (SOL) muscles [12], as well as SOL H-reflex amplitudes [13]

Summary

Introduction

Action observation (AO) and motor imagery (MI) are useful rehabilitation techniques for patients with neurological disorders. AO and MI are known to modulate those neural systems that relate to observed and imagined movements without action execution and muscle contraction. Fadiga et al reported that during MI of forearm flexion, MEPs in the biceps brachii muscle were increased while those in the opponens pollicis muscle, which is not recruited during forearm flexion, were unchanged [8].

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