Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans.

Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans. Research Abstract Details 

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Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans. Abstract Text:

M T Johnson,A N Kipnis,M C Lee,T J Ebner,

It is well known that during volitional sinusoidal tracking the long-latency reflex modulates in parallel with the volitional EMG activity. In this study, a series of experiments are reported demonstrating several conditions in which an uncoupling of reflex from volitional activity occurs. The paradigm consists of a visually guided task in which the subject tracked a sinusoid with the wrist. The movement was perturbed by constant torque or controlled velocity perturbations at 45 degrees intervals of the tracking phase. Volitional and reflex-evoked EMG and wrist displacement as functions of the tracking phase were recorded. The relationship of both short-latency (30-60 ms) and longer-latency (60-100 ms) reflex components to the volitional EMG was evaluated. In reflex tracking, the peak reflex amplitude occurs at phases of tracking which correspond to a maximum of wrist joint angular velocity in the direction of homonymous muscle shortening and a minimum of wrist compliance. Uncoupling of the reflex and volitional EMG was observed in three situations. First, during passive movement of the wrist through the sinusoidal tracking cycle perturbation-evoked long-latency stretch reflex peak is modulated as for normal, volitional tracking. However, with passive joint movement the volitional EMG modulation is undetectable. Second, a subset of subjects demonstrate a normally modulated and positioned long-latency reflex with a single peak. However, these subjects have distinct bimodal peaks of volitional EMG. Third, the imposition of an anti-elastic load (positive position feedback) shifts the volitional EMG envelope by as much as 180 degrees along the tracking phase when compared with conventional elastic loading. Yet the long-latency reflex peak remains at its usual phase in the tracking cycle, corresponding to the maximal velocity in the direction of muscle shortening. Furthermore, comparison of the results from elastic and anti-elastic loads reveals a dissociation of short- and long-latency reflex activity, with the short-latency reflex shifting with the volitional EMG envelope. Comparable results were also obtained for controlled velocity perturbations used to control for changes in joint compliance. The uncoupling of the reflex and volitional EMG activity in the present series of experiments points to a flexible relationship between reflex and volitional control systems, altered by peripheral input and external load.

Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans. Publishing Authors By Initials

MT Johnson,AN Kipnis,MC Lee,TJ Ebner,

For similar musculoskeletal system: skeleton: joints: hand joints: wrist joint research abstracts see: musculoskeletal system: skeleton: joints: hand joints: wrist joint research

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Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans. Journal Published:

PUBLICATION TYPE: Research Support, U.S. Gov't,

Journal: Experimental brain research. Experimentelle Hirnfo

VOLUME: 96

Page Numbers: 347-62

Journal Abbreviation:

ISSN: 0014-4819

DAY: 15

MONTH: 02

YEAR: 1993

Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans. Information

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LANGUAGE: eng

NlmUniqueID: 43312

Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans. Keywords Mesh Terms:

KEYWORDS: Wrist Joint

MESH TERMS: physiology

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Grant and Affiliation Information for Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans.

AFFILIATION: Department of Neurology, University of Minnesota, Minneapolis 55455.

Country: GERMANY

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MEDLINETA: Exp Brain Res

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