Distinct coordinate systems for adaptations of movement direction and extent.

Eugene Poh, Timothy J. Carroll, Aymar de Rugy
Journal of Neurophysiology. 2017-11-01; 118(5): 2670-2686
DOI: 10.1152/jn.00326.2016

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1. J Neurophysiol. 2017 Nov 1;118(5):2670-2686. doi: 10.1152/jn.00326.2016. Epub
2017 Aug 23.

Distinct coordinate systems for adaptations of movement direction and extent.

Poh E(1)(2), Carroll TJ(2), de Rugy A(3)(4).

Author information:
(1)Department of Psychology, Princeton University, Princeton, New Jersey.
(2)Centre for Sensorimotor Performance, School of Human Movement and Nutrition
Sciences, The University of Queensland, Brisbane, Queensland, Australia; and.
(3)Centre for Sensorimotor Performance, School of Human Movement and Nutrition
Sciences, The University of Queensland, Brisbane, Queensland, Australia; and
.
(4)Institut de Neurosciences Cognitives et Intégratives d’Aquitaine, CNRS UMR
5287, Université de Bordeaux, Bordeaux, France.

Learned compensations for perturbed visual feedback of movement extent and
direction generalize differently to unpracticed movement directions, which
suggests different underlying neural mechanisms. Here we investigated whether
gain and rotation adaptations are consistent with representation in different
coordinate systems. Subjects performed a force-aiming task with the wrist and
learned different gains or rotations for different force directions.
Generalization was tested without visual feedback for the same extrinsic
directions but with the forearm in a different pronation-supination orientation.
When the change in forearm orientation caused the adapted visuomotor map to
conflict in extrinsic and joint-based coordinates, rotation generalization
occurred in extrinsic coordinates but with reduced magnitude. In contrast, gain
generalization appeared reduced and phase shifted. When the forearm was rotated
further, such that all imposed perturbations aligned in both joint-based and
extrinsic coordinates in both postures, rotation generalization was further
reduced, whereas there was neither reduction nor phase shift in the pattern of
extent generalization. These results show that rotation generalization was
expressed in extrinsic coordinates, and that generalization magnitude was
modulated by posture. In contrast, gain generalization appeared to depend on
target direction defined by an integrated combination of extrinsic and
joint-based coordinates and was not reduced substantially by posture changes
alone. Although the quality of the model fit underlying our interpretation
prevents us from making strong conclusions, the data suggest that adaptations of
movement direction and extent are represented according to distinct coordinate
systems.NEW & NOTEWORTHY Visuomotor gain and rotation adaptations generalize
differently to novel movement directions, which suggests different neural
mechanisms. When extrinsic and joint-based coordinates are effectively
dissociated in an isometric aiming task, we find that they also generalize in
different coordinate systems. Specifically, rotation generalized in extrinsic
coordinates and decayed as posture departed from that adopted during adaptation.
In contrast, gain generalization was expressed according to mixed
extrinsic/joint-based coordinates and was not substantially reduced by postural
changes.

Copyright © 2017 the American Physiological Society.

DOI: 10.1152/jn.00326.2016
PMCID: PMC5672543 [Available on 2018-11-01]
PMID: 28835524 [Indexed for MEDLINE]


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