Deciphering the functional role of spatial and temporal muscle synergies in whole-body movements

Ioannis Delis,Stefano Panzeri,Pauline M Hilt,Thierry Pozzo,Bastien Berret

doi:10.1038/s41598-018-26780-z

Abstract

Voluntary movement is hypothesized to rely on a limited number of muscle synergies, the recruitment of which translates task goals into effective muscle activity. In this study, we investigated how to analytically characterize the functional role of different types of muscle synergies in task performance. To this end, we recorded a comprehensive dataset of muscle activity during a variety of whole-body pointing movements. We decomposed the electromyographic (EMG) signals using a space-by-time modularity model which encompasses the main types of synergies. We then used a task decoding and information theoretic analysis to probe the role of each synergy by mapping it to specific task features. We found that the temporal and spatial aspects of the movements were encoded by different temporal and spatial muscle synergies, respectively, consistent with the intuition that there should a correspondence between major attributes of movement and major features of synergies. This approach led to the development of a novel computational method for comparing muscle synergies from different participants according to their functional role. This functional similarity analysis yielded a small set of temporal and spatial synergies that describes the main features of whole-body reaching movements.

Highlights

Human motor control has been hypothesized to rely on a limited set of building blocks, termed muscle synergies, motor primitives or more generically modules[1,2,3,4,5,6,7]
The core idea behind this method is that synergies which are different in muscle composition or temporal profile, can be clustered as similar if they relate to the same task parameters, i.e. they can be considered as functionally equivalent if they have similar roles in task performance
We examined the functional similarity of the extracted synergies across subjects and determined a small set of spatial and temporal synergies whose single-trial activations encode complementary task parameters and describe the muscle activity that is necessary for the distinct representation of the whole-body pointing movements

Summary

Introduction

Human motor control has been hypothesized to rely on a limited set of building blocks, termed muscle synergies, motor primitives or more generically modules[1,2,3,4,5,6,7]. Here we link the modular decomposition to its functional role, i.e. task performance, by asking what task information is carried by each one of the identified synergies (spatial or temporal). The core idea behind this method is that synergies which are different in muscle composition or temporal profile, can be clustered as similar if they relate to the same task parameters, i.e. they can be considered as functionally equivalent if they have similar roles in task performance. Such considerations of motor equivalence trace back to foundational studies in motor control[2,18,28]. Our study provides a detailed analytical account and interpretation of the functional significance of spatial and temporal muscle synergies

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Conclusion