Specific modulation of corticomuscular coherence during submaximal voluntary isometric, shortening and lengthening contractions

Dorian Glories,David Amarantini,Julien Duclay,Mathias Soulhol

doi:10.1038/s41598-021-85851-w

Abstract

During voluntary contractions, corticomuscular coherence (CMC) is thought to reflect a mutual interaction between cortical and muscle oscillatory activities, respectively measured by electroencephalography (EEG) and electromyography (EMG). However, it remains unclear whether CMC modulation would depend on the contribution of neural mechanisms acting at the spinal level. To this purpose, modulations of CMC were compared during submaximal isometric, shortening and lengthening contractions of the soleus (SOL) and the medial gastrocnemius (MG) with a concurrent analysis of changes in spinal excitability that may be reduced during lengthening contractions. Submaximal contractions intensity was set at 50% of the maximal SOL EMG activity. CMC was computed in the time–frequency domain between the Cz EEG electrode signal and the unrectified SOL or MG EMG signal. Spinal excitability was quantified through normalized Hoffmann (H) reflex amplitude. The results indicate that beta-band CMC and normalized H-reflex were significantly lower in SOL during lengthening compared with isometric contractions, but were similar in MG for all three muscle contraction types. Collectively, these results highlight an effect of contraction type on beta-band CMC, although it may differ between agonist synergist muscles. These novel findings also provide new evidence that beta-band CMC modulation may involve spinal regulatory mechanisms.

Highlights

During voluntary contractions, corticomuscular coherence (CMC) is thought to reflect a mutual interaction between cortical and muscle oscillatory activities, respectively measured by electroencephalography (EEG) and electromyography (EMG)
Added to the fact that, in most cases, the discharge rate of motor units decreases during lengthening compared with shortening c ontractions[13,14], these findings suggest that muscle oscillatory activity may differ according to the muscle contraction type, which could result in the modulation of the neural interactions shown by CMC analysis, especially during lengthening contractions
The subject was seated on an isokinetic ergometer and was asked to perform sub-maximal isometric, lengthening and shortening contractions while the EEG signal as well as soleus (SOL) and medial gastrocnemius (MG) EMG activities were recorded during every contraction in order to compute CMC

Summary

Introduction

Corticomuscular coherence (CMC) is thought to reflect a mutual interaction between cortical and muscle oscillatory activities, respectively measured by electroencephalography (EEG) and electromyography (EMG) It remains unclear whether CMC modulation would depend on the contribution of neural mechanisms acting at the spinal level. The control strategy employed by the nervous system during voluntary contractions can be investigated through the analysis of neural interactions between the brain and the contracting muscle Such interactions have been quantified by computing corticomuscular coherence (CMC) between electroencephalography (EEG) and surface electromyography (EMG) oscillatory activities[1]. Because Matsuya et al (2017)[10] showed that the amplitude of CMC decreased while recurrent inhibition increased and Barrué-Belou et al (2018)[11] observed greater recurrent inhibition during lengthening contractions, we hypothesized that CMC would be lower during lengthening contractions compared with isometric and shortening contractions

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