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Author Notes:

Address for reprint requests and other correspondence: L. H. Ting, The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 313 Ferst Dr., Atlanta, GA 30332-0535; Email: lting@emory.edu

Author contributions: S.A.S. conception and design of research; S.A.S. performed experiments; S.A.S. analyzed data; S.A.S. and L.H.T. interpreted results of experiments; S.A.S. prepared figures; S.A.S. drafted manuscript; S.A.S. and L.H.T. edited and revised manuscript; S.A.S. and L.H.T. approved final version of manuscript.

The authors thank D. Joseph Jilk for implementing the perturbations and assisting with data collection.

No conflicts of interest, financial or otherwise, are declared by the author(s).

Subjects:

Research Funding:

This work was supported by National Institutes of Health (NIH) Grant R01-NS-058322 (to L. H. Ting).

S. A. Safavynia was supported by a Medical Scientist Training Program Fellowship (NIH Grant 5-T32-GM08169-24).

Keywords:

  • sensorimotor feedback
  • electromyography
  • motor control
  • posture and balance

Sensorimotor feedback based on task-relevant error robustly predicts temporal recruitment and multidirectional tuning of muscle synergies

Tools:

Journal Title:

Journal of Neurophysiology

Volume:

Volume 109, Number 1

Publisher:

, Pages 31-45

Type of Work:

Article | Post-print: After Peer Review

Abstract:

We hypothesized that motor outputs are hierarchically organized such that descending temporal commands based on desired task-level goals flexibly recruit muscle synergies that specify the spatial patterns of muscle coordination that allow the task to be achieved. According to this hypothesis, it should be possible to predict the patterns of muscle synergy recruitment based on task-level goals. We demonstrated that the temporal recruitment of muscle synergies during standing balance control was robustly predicted across multiple perturbation directions based on delayed sensorimotor feedback of center of mass (CoM) kinematics (displacement, velocity, and acceleration). The modulation of a muscle synergy's recruitment amplitude across perturbation directions was predicted by the projection of CoM kinematic variables along the preferred tuning direction(s), generating cosine tuning functions. Moreover, these findings were robust in biphasic perturbations that initially imposed a perturbation in the sagittal plane and then, before sagittal balance was recovered, perturbed the body in multiple directions. Therefore, biphasic perturbations caused the initial state of the CoM to differ from the desired state, and muscle synergy recruitment was predicted based on the error between the actual and desired upright state of the CoM. These results demonstrate that that temporal motor commands to muscle synergies reflect task-relevant error as opposed to sensory inflow. The proposed hierarchical framework may represent a common principle of motor control across motor tasks and levels of the nervous system, allowing motor intentions to be transformed into motor actions.

Copyright information:

© 2013 the American Physiological Society

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