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Output Units of Motor Behavior: An Experimental and Modeling Study
Journal article   Open access   Peer reviewed

Output Units of Motor Behavior: An Experimental and Modeling Study

E. P Loeb, S. F Giszter, P. Saltiel and E Bizzi and F. A Mussa-Ivaldi
Journal of cognitive neuroscience, v 12(1), pp 78-97
Jan 2000
DOI: https://doi.org/10.1162/08989290051137611
PMID: 10769307
url
https://doi.org/10.1162/08989290051137611View
Published, Version of Record (VoR) Open

Abstract

Cognitive approaches to motor control typically concern sequences of discrete actions without taking into account the stunning complexity of the geometry and dynamics of the muscles. This begs the question: Does the brain convert the intricate, continuous-time dynamics of the muscles into simpler discrete units of actions, and if so, how? One way for the brain to form discrete units of behavior from muscles is through the synergistic co-activation of muscles. While this possibility has long been known, the composition of potential muscle synergies has remained elusive. In this paper, we have focused on a method that allowed us to examine and compare the limb stabilization properties of all possible muscle combinations. We found that a small set (as few as 23 out of 65,536) of all possible combinations of 16 limb muscles are robust with respect to activation noise: these muscle combinations could stabilize the limb at predictable, restricted portions of the workspace in spite of broad variations in the force output of their component muscles. The locations at which the robust synergies stabilize the limb are not uniformly distributed throughout the leg's workspace, but rather, they cluster at four workspace areas. The simulated robust synergies are similar to the actual synergies we have previously found to be generated by activation of the spinal cord. Thus, we have developed a new analytical method that enabled us to select a few muscle synergies with interesting properties out of the set of possible muscle combinations. Beyond this, the identification of robustness as a common property of the synergies in simple motor behaviors will open the way to the study of dynamic stability, which is an important and distinct property of the vertebrate motor-control system.

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41 citations in Web of Science
45 citations in Scopus

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Collaboration types
Domestic collaboration
Web of Science research areas
Neurosciences
Psychology, Experimental
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