Persistence of Motor Adaptation During Constrained, Multi-Joint,
Arm Movements
ROBERT A. SCHEIDT, DAVID J. REINKENSMEYER, MICHAEL A. CONDITT, W. ZEV RYMER, AND
FERDINANDO A. MUSSA-IVALDI
Department of Biomedical Engineering, Northwestern University, Evanston 60622; and Sensory Motor Performance
Program, Rehabilitation Institute of Chicago, Chicago, Illinois 60611
Received 16 December 1999; accepted in final form 28 April 2000
Scheidt, Robert A., David J. Reinkensmeyer, Michael A. Conditt,
W. Zev Rymer, and Ferdinando A. Mussa-Ivaldi. Persistence of
motor adaptation during constrained, multi-joint, arm movements. J
Neurophysiol 84: 853-862, 2000.
ABSTRACT
We studied the stability of changes
in motor performance associated with adaptation to a novel dynamic
environment during goal-directed movements of the dominant arm.
Eleven normal, human subjects made targeted reaching movements in
the horizontal plane while holding the handle of a two-joint robotic
manipulator. This robot was programmed to generate a novel viscous
force field that perturbed the limb perpendicular to the desired direc-tion
of movement. Following adaptation to this force field, we sought
to determine the relative role of kinematic errors and dynamic criteria
in promoting recovery from the adapted state. In particular, we com-pared
kinematic and dynamic measures of performance when kine-matic
errors were allowed to occur after removal of the viscous fields,
or prevented by imposing a simulated, mechanical “channel” on
movements. Hand forces recorded at the handle revealed that when
kinematic errors were prevented from occurring by the application of
the channel, recovery from adaptation to the novel field was much
slower compared with when kinematic aftereffects were allowed to
take place. In particular, when kinematic errors were prevented,
subjects persisted in generating large forces that were unnecessary to
generate an accurate reach. The magnitude of these forces decreased
slowly over time, at a much slower rate than when subjects were
allowed to make kinematic errors. This finding provides strong ex-perimental
evidence that both kinematic and dynamic criteria influ-ence
motor adaptation, and that kinematic-dependent factors play a
dominant role in the rapid loss of adaptation after restoring the
original dynamics.
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