Generalization of visuomotor adaptation to different muscles is less efficient: Experiment and model

1. Hum Mov Sci. 2010 Oct;29(5):684-700. doi: 10.1016/j.humov.2010.01.008. Epub 2010
Jul 31.

Generalization of visuomotor adaptation to different muscles is less efficient:
experiment and model.

de Rugy A(1).

Author information:
(1)Perception and Motor Systems Laboratory, School of Human Movement Studies,
University of Queensland, Brisbane, Australia.

Reaching to visual targets engages the nervous system in a series of
transformations between sensory information and motor commands to muscles. We
recently showed that visuomotor adaptation requiring modulation of the activity
of the same muscles is more efficient than adaptation requiring a transition to
different muscles. Here I specifically tested for adaptation at the level of the
final transformation into muscle activation by assessing generalization to
unpracticed areas of the workspace, and propose a computational model with
modulation of muscle synergies. In the experiment, a visuomotor rotation was
applied during a center-out isometric torque production task carefully configured
such that adaptation and generalization could be achieved either by only
rescaling the contribution of the same muscles, or by additionally requiring the
recruitment of different muscles. Consistent with our previous finding, the time
course of directional errors revealed that the degree of adaptation was
substantially lower (by 28.1%) for the latter case. More importantly, directional
error obtained for generalization that required, in principle, to recruit
different muscles from these implicated in the adaptation was more than twice
that of other generalization areas. Taken together, these results suggest that
modulation within an original muscle synergy contributed to visuomotor
adaptation, and that synergy recomposition imposed a limitation on both
adaptation and generalization. I reproduced these results with a model of the
sensorimotor transformation which includes two population codes, one for the
sensory network and one for the motor network. Muscle synergies are defined as
linear combination of muscles by connections of the motor network, and modulation
of these synergies are elicited by adaptation of the weight of these connections.
Finally, I speculate that the limitation imposed on synergy recomposition
originates in the balance of inhibitory and excitatory mechanisms that operate at
different levels of the nervous system, and that contribute to the functional
organization of muscle recruitment by focusing activity on relevant muscles.

Copyright © 2010 Elsevier B.V. All rights reserved.

DOI: 10.1016/j.humov.2010.01.008
PMID: 20674052 [Indexed for MEDLINE]

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