Modulation of the stretch reflex during volitional sinusoidal tracking in parkinson's disease

M. T V Johnson, A. N. Kipnis, M. C. Lee, R. B. Loewenson, T. J. Ebner

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Sinusoidal visually-guided wrist traking, in normal and parkinsonian subjects, was perturbed by torque transients every 90° throughout the movement. Long-latency stretch reflex and volitional EMG amplitude modulations were assessed as functions of the tracking phase. Reflex Modulation during tracking, both in wrist flexor and extensor muscles, was found to differ significantly between parkinsonian and normal subjects. In the Parkinsonian group, the abnormality consisted of an increased reflex activity during tracking phases in which the muscle was lengthening. At these Phases the reflex generated torque is opposite in direction to the volitionally generated torque and the tracking movement. No differences in the unperturbed volitional EMG modulation were observed between groups for this error constrained tracking paradigm. Significant correlations were found between ratings of bradykinesia and the amount of abnormal reflex modulation in the wrist flexor. These data suggest that a component of bradykinesia results from a defective coordination of supraspinal reflex and volitional control systems.

Original languageEnglish (US)
Pages (from-to)443-460
Number of pages18
Issue number1
StatePublished - Feb 1991

Bibliographical note

Funding Information:
We are indebted to the patients who consented to testing. Michael McPhee provided assistance with graphics. The work was funded by EMPI Inc., American Parkinson Disease Association, Minnesota Medical Foundation, and Mr Hal Seth.

Copyright 2010 Elsevier B.V., All rights reserved.

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