High-Frequency Intermuscular Coherence between Arm Muscles during Robot-Mediated Motor Adaptation.

Sara Pizzamiglio,Duncan L Turner,Martina De Lillo,Usman Naeem,Hassan Abdalla

doi:10.3389/fphys.2016.00668

Sara Pizzamiglio, Duncan L Turner + Show 3 more

Open Access

https://doi.org/10.3389/fphys.2016.00668

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Abstract

Adaptation of arm reaching in a novel force field involves co-contraction of upper limb muscles, but it is not known how the co-ordination of multiple muscle activation is orchestrated. We have used intermuscular coherence (IMC) to test whether a coherent intermuscular coupling between muscle pairs is responsible for novel patterns of activation during adaptation of reaching in a force field. Subjects (N = 16) performed reaching trials during a null force field, then during a velocity-dependent force field and then again during a null force field. Reaching trajectory error increased during early adaptation to the force-field and subsequently decreased during later adaptation. Co-contraction in the majority of all possible muscle pairs also increased during early adaptation and decreased during later adaptation. In contrast, IMC increased during later adaptation and only in a subset of muscle pairs. IMC consistently occurred in frequencies between ~40–100 Hz and during the period of arm movement, suggesting that a coherent intermuscular coupling between those muscles contributing to adaptation enable a reduction in wasteful co-contraction and energetic cost during reaching.

Highlights

Motor adaptation to a physical disturbance is a dynamic process and involves a complex interaction of central and peripheral systems (Lemon, 2008; Rosenbaum, 2009; Gandolla et al, 2014)
The present study describes the development of patterns of coherent muscle activity across a range of arm muscles during a force field motor adaptation paradigm
The findings are novel for this type of motor skill learning and the use of intermuscular coherence (IMC) in this study is an alternative to the traditional measures of integrated muscle activation or co-contraction/co-contraction

Summary

Introduction

Motor adaptation to a physical disturbance is a dynamic process and involves a complex interaction of central (neural) and peripheral (muscular) systems (Lemon, 2008; Rosenbaum, 2009; Gandolla et al, 2014). Motor adaptation of arm reaching to force field perturbations involves changes in the activation pattern of upper limb muscles that may serve to reduce online errors and may represent the development of a new internal model (Osu et al, 2003; Milner and Franklin, 2005; Orban de Xivry et al, 2013). Indices such as co-contraction ratios have been computed to give an estimate of energy-expensive wasted co-contraction (Darainy and Ostry, 2008; Huang and Ahmed, 2014) or put forward as a mechanism for stiffening the arm during motor adaptation (Milner et al, 1995; Koshland et al, 2000) Whilst these techniques can describe a “muscle output” signal, they may only indirectly infer that there are changes in input neural signals during motor adaptation. We use IMC to test the hypothesis that there is an increase in coherent muscle activation during motor adaptation and that it is related to formation of a new behavioral optimization strategy reducing reaching errors as well as cocontraction

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