Document Detail

Reciprocal and coactivation commands for fast wrist movements.
MedLine Citation:
PMID:  1644129     Owner:  NLM     Status:  MEDLINE    
According to the equilibrium-point hypothesis, movements are produced by means of displacement of the invariant torque/angle characteristic (IC) of the joint and change in its slope. Displacement is produced via the central reciprocal (R) command while the coactivation (C) command specifies the slope of the IC. Neurophysiologically, the R command is associated with reciprocal changes in the membrane potentials of agonist and antagonist motoneurons while the C command is associated with their simultaneous depolarisation. These commands were investigated in single joint wrist movements by perturbation methods. Subjects normally made free flexion movements to a target at 30 degrees but on random trials they were either opposed by a spring-like load or assisted by a load. The former was generated using negative linear position feedback; the latter using positive position feedback to a torque motor. Subjects were instructed not to correct errors arising from perturbations. Both peak velocity and EMG patterns were strongly affected by load conditions. Subjects undershot or overshot the target when opposing or assisting loads were presented, respectively. However, after removing the load (700 ms later), the target position was regained indicating that the IC was stable despite the perturbation. In two other experiments, subjects initially trained to reach the target with opposing or assisting loads, while on random trials, the load was not presented. Depending on training conditions, the subject shifted the IC by different amounts. The slope of the IC varied independently of the magnitude of its positional shift. We conclude that R and C commands can be specified independently.(ABSTRACT TRUNCATED AT 250 WORDS)
M F Levin; A G Feldman; T E Milner; Y Lamarre
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Experimental brain research     Volume:  89     ISSN:  0014-4819     ISO Abbreviation:  Exp Brain Res     Publication Date:  1992  
Date Detail:
Created Date:  1992-09-08     Completed Date:  1992-09-08     Revised Date:  2013-12-13    
Medline Journal Info:
Nlm Unique ID:  0043312     Medline TA:  Exp Brain Res     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  669-77     Citation Subset:  IM    
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MeSH Terms
Brain / physiology*
Functional Laterality
Membrane Potentials
Middle Aged
Models, Neurological
Motor Activity*
Motor Neurons / physiology*
Muscles / innervation*
Wrist Joint / physiology*

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