Changes in wrist muscle activity with forearm posture: Implications for the study of sensorimotor transformations

Aymar de Rugy, Rahman Davoodi, Timothy J. Carroll
Journal of Neurophysiology. 2012-12-01; 108(11): 2884-2895
DOI: 10.1152/jn.00130.2012

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1. J Neurophysiol. 2012 Dec;108(11):2884-95. doi: 10.1152/jn.00130.2012. Epub 2012
Sep 12.

Changes in wrist muscle activity with forearm posture: implications for the study
of sensorimotor transformations.

de Rugy A(1), Davoodi R, Carroll TJ.

Author information:
(1)Centre for Sensorimotor Neuroscience, School of Human Movement Studies, The
University of Queensland, Brisbane, Queensland, Australia.

The primate wrist is an ideal model system for studying the reference frames in
which movements are coded within the central nervous system, as a simple rotation
of the forearm allows dissociation between extrinsic and body-referenced
coordinates. Important information regarding coordinate frame transformations has
been obtained using this system, particularly from studies involving
extracellular cortical and spinal recordings from monkeys. Because preferred
directions of muscle use were reported to rotate by less than half of the joint
rotation, the system was considered to dissociate three reference frames:
extrinsic (direction of movement in space), muscle (activity of muscles), and
joint (angle of the wrist joint). However, given the relatively minor changes in
reported muscle biomechanics with human forearm rotation, the reported
distinction between joint space and muscle space is surprisingly large. Here, we
reassessed patterns of wrist muscle activity with changes in forearm posture in
humans, during an isometric force-aiming task with a device that enabled
stringent control of the musculoskeletal configuration. Results show that the
preferred directions for wrist muscle activation closely follow forearm
orientation (i.e., by 88%). Control experiments confirmed this, whether the hand
was clamped passively by a device or grasped a handle. Furthermore, the remaining
12% discrepancy between intended changes in wrist orientation and muscle use also
occurred for muscle-pulling directions obtained by intramuscular electrical
stimulation. The findings prompt reconsideration of data based on the previously
reported dissociation between joint space and muscle space and have critical
implications for future investigations of sensorimotor transformations and their
adaptation using the wrist.

DOI: 10.1152/jn.00130.2012
PMID: 22972965 [Indexed for MEDLINE]

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