Changes in muscle directional tuning parallel feedforward adaptation to a visuomotor rotation

Aymar de Rugy, Timothy J. Carroll
Exp Brain Res. 2010-05-09; 203(4): 701-709
DOI: 10.1007/s00221-010-2280-9

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1. Exp Brain Res. 2010 Jun;203(4):701-9. doi: 10.1007/s00221-010-2280-9. Epub 2010
May 9.

Changes in muscle directional tuning parallel feedforward adaptation to a
visuomotor rotation.

de Rugy A(1), Carroll TJ.

Author information:
(1)Perception and Motor Systems Laboratory, School of Human Movement Studies,
University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia.

When people learn to reach in a novel sensorimotor environment, there are changes
in the muscle activity required to achieve task goals. Here, we assessed the time
course of changes in muscle directional tuning during acquisition of a new
mapping between visual information and isometric force production in the absence
of feedback-based error corrections. We also measured the influence of visuomotor
adaptation on corticospinal excitability, to test whether any changes in muscle
directional tuning are associated with adaptations in the final output components
of the sensorimotor control system. Nine right-handed subjects performed a
ballistic, center-out isometric target acquisition task with the right wrist (16
targets spaced every 22.5 degrees in the joint space). Surface electromyography
was recorded from four major wrist muscles, and motor evoked potentials induced
by transcranial magnetic stimulation were measured at baseline, after task
execution in the absence of the rotation (A1), after adaptation to the rotation
(B), and after a final block of trials without rotation (A2). Changes in the
directional tuning of muscles closely matched the rotation of the directional
error in force, indicating that the functional contribution of muscles remained
consistent over the adaptation period. In contrast to previous motor learning
studies, we found only minor changes in the amount of muscular activity and no
increase in corticospinal excitability. These results suggest that increased
muscle co-activation occurs only when the dynamics of the limb are perturbed
and/or that online error corrections or altered force requirements are necessary
to elicit a component of the adaptation in the final steps of the transformation
between motor goal and muscle activation.

DOI: 10.1007/s00221-010-2280-9
PMID: 20454956 [Indexed for MEDLINE]

Auteurs Bordeaux Neurocampus