Modular Organization of Muscle Synergies to Achieve Movement Behaviors.

Kunkun Zhao,Zihan Wang,Jiankang Wu,Zhisheng Zhang,Haiying Wen

doi:10.1155/2019/8130297

Kunkun Zhao, Zihan Wang + Show 3 more

Open Access

https://doi.org/10.1155/2019/8130297

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Abstract

Muscle synergy has been applied to comprehend how the central nervous system (CNS) controls movements for decades. However, it is not clear about the motion control mechanism and the relationship between motions and muscle synergies. In this paper, we designed two experiments to corroborate the hypothesis: (1) motions can be decomposed to motion primitives, which are driven by muscle synergy primitives and (2) variations of motion primitives in direction and scale are modulated by activation coefficients rather than muscle synergy primitives. Surface electromyographic (EMG) signals were recorded from nine muscles of the upper limb. Nonnegative matrix factorization (NMF) was applied to extract muscle synergy vectors and corresponding activation coefficients. We found that synergy structures of different movement patterns were similar (α=0.05). The motion modulation indexes (MMI) among movement patterns in reaching movements showed apparent differences. Merging coefficients and reconstructed similarity of synergies between simple motions and complex motions were significant. This study revealed the motion control mechanism of the CNS and provided a rehabilitation and evaluation method for patients with motor dysfunction in exercise and neuroscience.

Highlights

A large amount of research has reported that the central nervous system (CNS) uses a dimensionality reduction pattern to coactivate a set of motion primitives (MP) to achieve daily activity living (DAL)
Based on the prior research, two hypotheses are tested: (1) any motion can be decomposed to motion primitives, which are driven by muscle synergy primitives and (2) variations of motion primitives in direction and scale are modulated by activation coefficients rather than muscle synergy primitives
According to the criteria described above, we identified three synergies (2.82 ± 0.40, corresponding variance accounted for (VAF) is 0.94 ± 0.01) in reaching movement (E2) for further analysis

Summary

Introduction

A large amount of research has reported that the CNS uses a dimensionality reduction pattern to coactivate a set of motion primitives (MP) to achieve daily activity living (DAL). Modularity or muscle synergy as a building block, both structural and computational, exhibited feasibility for achieving motion control [2]. It has been proven in animal experiments, such as in cats, frogs, and monkeys. E study in various human locomotions, consisting of walking and running at different speeds, walking forward or backward, and walking under different loading conditions and different styles (rectilinear and curvilinear trajectories) [7, 8], showed that motions were driven by combining a few muscle synergy primitives. D’Avella et al [13, 14] analyzed and summarized the movements of point-to-point at different speeds, loads, forearm postures, and via-point movements, showing that the CNS achieved a goal by combining a set of building blocks (muscle synergy primitives). Based on the prior research, two hypotheses are tested: (1) any motion can be decomposed to motion primitives, which are driven by muscle synergy primitives and (2) variations of motion primitives in direction and scale are modulated by activation coefficients rather than muscle synergy primitives

Materials and Methods

Data Analysis

Analysis of E2

Analysis of E1