Faculty Collaboration Database

Separate adaptive mechanisms for controlling trajectory and final position in reaching. J Neurophysiol 2007 Dec;98(6):3600-13

Date

10/05/2007

Pubmed ID

17913996

DOI

10.1152/jn.00121.2007

Scopus ID

2-s2.0-37549031332 (requires institutional sign-in at Scopus site)   119 Citations

Abstract

We examined control of the hand's trajectory (direction and shape) and final equilibrium position in horizontal planar arm movements by quantifying transfer of learned visuomotor rotations between two tasks that required aiming the hand to the same spatial targets. In a trajectory-reversal task ("slicing"), the hand reversed direction within the target and returned to the origin. In a positioning task ("reaching"), subjects moved the hand to the target and held it there; cursor feedback was provided only after movement ended to isolate learning of final position from trajectory direction. We asked whether learning acquired in one task would transfer to the other. Transfer would suggest that the hand's entire trajectory, including its endpoint, was controlled using a common spatial plan. Instead we found minimal transfer, suggesting that the brain used different representations of target position to specify the hand's initial trajectory and its final stabilized position. We also observed asymmetrical practice effects on hand trajectory, including systematic curvature of reaches made after rotation training and hypermetria of untrained slice reversals after reach training. These are difficult to explain with a unified control model, but were replicated in computer simulations that specified the hand's initial trajectory and its final equilibrium position. Our results suggest that the brain uses different mechanisms to plan the hand's initial trajectory and final position in point-to-point movements, that it implements these control actions sequentially, and that trajectory planning does not account for specific impedance values to be implemented about the final stabilized posture.

Author List

Scheidt RA, Ghez C

Author

Robert Scheidt BS,MS,PhD Associate Professor in the Biomedical Engineering department at Marquette University

MESH terms used to index this publication - Major topics in bold

Adaptation, Physiological
Adult
Aged
Arm
Computer Simulation
Data Interpretation, Statistical
Electromyography
Female
Functional Laterality
Humans
Imagination
Joints
Learning
Male
Middle Aged
Posture
Psychomotor Performance
Rotation