A Joseph Threlkeld4
Douglas Powell3
4A Joseph Threlkeld
3Douglas Powell
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OBJECTIVE To examine the correlation between rigidity and interaction of stretch reflex and shortening reaction during passive movements of the wrist and to compare this correlation with that between rigidity and stretch reflex alone. METHODS Twelve subjects with Parkinson's disease participated in the study in Off-medication and On-medication states. A(More)
OBJECTIVE Quantify the enhancement of parkinsonian rigidity associated with a contralateral activation maneuver. METHODS Twelve subjects with PD and eight controls participated in the study protocol. Subjects' tested hand was displaced by a servo-motor throughout wrist flexion and extension motions of 60° without and with a concurrent gripping activation(More)
OBJECTIVE Quantify the effects of increased amplitude and rate of muscle stretch on parkinsonian rigidity. METHODS Eighteen subjects with Parkinson's disease participated in this study. Subjects' tested hand was passively displaced through 60° and 90° ranges of wrist flexion and extension at velocities of 50°/s and 280°/s in both treated and untreated(More)
Parkinsonian rigidity is characterized by an increased resistance of a joint to externally imposed motion that remains uniform with changing joint angle. Two candidate mechanisms are proposed for the uniformity of rigidity, involving neural-mediated excitation of shortening muscles, i.e., shortening reaction (SR), or inhibition of stretched muscles, i.e.,(More)
Phase-dependent and task-dependent modulation of reflexes has been extensively demonstrated in leg muscles during locomotory activity. In contrast, the modulation of reflex responses of hand muscles during rhythmic movement is poorly documented. The objective of this study was to determine whether comparable reflex modulation occurs in muscles controlling(More)
Bradykinesia is a cardinal symptom of Parkinson's disease (PD). Both aging and disease are shown to be associated with decreased adaptability to environmental stresses characterized by reduced complexity (or increased regularity) of biorhythms. The purpose of this study was to investigate the regularity of movement in individuals with PD, and the effect of(More)
The strategy of human manual control is investigated in balancing an inverted pendulum under time-delay constraints. Experiments show that as the task becomes more difficult due to the increase in time delay, the human operator adopts a more discrete-like strategy. Interpretation of the discrete-control mechanism is provided by relating the observed human(More)