The synergistic organization of muscle recruitment constrains visuomotor adaptation
Journal of Neurophysiology. 2009-05-01; 101(5): 2263-2269
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1. J Neurophysiol. 2009 May;101(5):2263-9. doi: 10.1152/jn.90898.2008. Epub 2009 Feb
The synergistic organization of muscle recruitment constrains visuomotor
de Rugy A(1), Hinder MR, Woolley DG, Carson RG.
(1)Perception and Motor Systems Laboratory, School of Human Movement Studies,
Room 424, Building 26, University of Queensland, St Lucia QLD, 4072, Australia.
Reaching to visual targets engages the nervous system in a series of
transformations between sensory information and motor commands. That which
remains to be determined is the extent to which the processes that mediate
sensorimotor adaptation to novel environments engage neural circuits that
represent the required movement in joint-based or muscle-based coordinate
systems. We sought to establish the contribution of these alternative
representations to the process of visuomotor adaptation. To do so we applied a
visuomotor rotation during a center-out isometric torque production task that
involved flexion/extension and supination/pronation at the elbow-joint complex.
In separate sessions, distinct half-quadrant rotations (i.e., 45 degrees ) were
applied such that adaptation could be achieved either by only rescaling the
individual joint torques (i.e., the visual target and torque target remained in
the same quadrant) or by additionally requiring torque reversal at a contributing
joint (i.e., the visual target and torque target were in different quadrants).
Analysis of the time course of directional errors revealed that the degree of
adaptation was lower (by approximately 20%) when reversals in the direction of
joint torques were required. It has been established previously that in this task
space, a transition between supination and pronation requires the engagement of a
different set of muscle synergists, whereas in a transition between flexion and
extension no such change is required. The additional observation that the initial
level of adaptation was lower and the subsequent aftereffects were smaller, for
trials that involved a pronation-supination transition than for those that
involved a flexion-extension transition, supports the conclusion that the process
of adaptation engaged, at least in part, neural circuits that represent the
required motor output in a muscle-based coordinate system.
PMID: 19225174 [Indexed for MEDLINE]