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Author Notes:

Address for reprint requests and other correspondence: L. H. Ting, Wallace H. Coulter Dept. of Biomedical Engineering, Georgia Inst. of Technology and Emory Univ., 313 Ferst Dr., Atlanta, GA 30332-0535 (e-mail: lting@emory.edu).

Subjects:

Research Funding:

This work is supported by National Institutes of Health (NIH) Grant R01 NS-058322 to L. H. Ting. S. A. Safavynia is supported by a Medical Scientist Training Program Fellowship (NIH 5 T32 GM-08169-24).

Keywords:

  • balance
  • center of mass
  • electromyography
  • motor control

Task-level feedback can explain temporal recruitment of spatially fixed muscle synergies throughout postural perturbations

Tools:

Journal Title:

Journal of Neurophysiology

Volume:

Volume 107, Number 1

Publisher:

, Pages 159-177

Type of Work:

Article | Post-print: After Peer Review

Abstract:

Recent evidence suggests that complex spatiotemporal patterns of muscle activity can be explained with a low-dimensional set of muscle synergies or M-modes. While it is clear that both spatial and temporal aspects of muscle coordination may be low dimensional, constraints on spatial versus temporal features of muscle coordination likely involve different neural control mechanisms. We hypothesized that the low-dimensional spatial and temporal features of muscle coordination are independent of each other. We further hypothesized that in reactive feedback tasks, spatially fixed muscle coordination patterns—or muscle synergies—are hierarchically recruited via time-varying neural commands based on delayed task-level feedback. We explicitly compared the ability of spatially fixed (SF) versus temporally fixed (TF) muscle synergies to reconstruct the entire time course of muscle activity during postural responses to anterior-posterior support-surface translations. While both SF and TF muscle synergies could account for EMG variability in a postural task, SF muscle synergies produced more consistent and physiologically interpretable results than TF muscle synergies during postural responses to perturbations. Moreover, a majority of SF muscle synergies were consistent in structure when extracted from epochs throughout postural responses. Temporal patterns of SF muscle synergy recruitment were well-reconstructed by delayed feedback of center of mass (CoM) kinematics and reproduced EMG activity of multiple muscles. Consistent with the idea that independent and hierarchical low-dimensional neural control structures define spatial and temporal patterns of muscle activity, our results suggest that CoM kinematics are a task variable used to recruit SF muscle synergies for feedback control of balance.

Copyright information:

© 2012 the American Physiological Society

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