Abstract
Postural instability is one of the major symptoms of Parkinson's disease. Here, we assimilated a model of intermittent delay feedback control during quiet standing into postural sway data from healthy young and elderly individuals as well as patients with Parkinson's disease to elucidate the possible mechanisms of instability. Specifically, we estimated the joint probability distribution of a set of parameters in the model using the Bayesian parameter inference such that the model with the inferred parameters can best-fit sway data for each individual. It was expected that the parameter values for three populations would distribute differently in the parameter space depending on their balance capability. Because the intermittent control model is parameterized by a parameter associated with the degree of intermittency in the control, it can represent not only the intermittent model but also the traditional continuous control model with no intermittency. We showed that the inferred parameter values for the three groups of individuals are classified into two major groups in the parameter space: one represents the intermittent control mostly for healthy people and patients with mild postural symptoms and the other the continuous control mostly for some elderly and patients with severe postural symptoms. The results of this study may be interpreted by postulating that increased postural instability in most Parkinson's patients and some elderly persons might be characterized as a dynamical disease.
Highlights
Symptoms associated with postural instability are common in patients with Parkinson’s disease, and they become more prominent scitation.org/journal/cha with disease progression, which causes falls and diminished quality of life.[4]
We showed that the inferred parameter values for the three groups of individuals are classified into two major groups in the parameter space: one represents the intermittent control mostly for healthy people and patients with mild postural symptoms and the other the continuous control mostly for some elderly and patients with severe postural symptoms
The intermittent delay feedback control model was assimilated into postural sway data from healthy young and elderly subjects as well as patients with Parkinson’s disease
Summary
Symptoms associated with postural instability are common in patients with Parkinson’s disease, and they become more prominent scitation.org/journal/cha with disease progression, which causes falls and diminished quality of life.[4] Contrary to popular belief, neuromechanical mechanisms of human upright posture during quiet stance are still subject to debate. The intermittent time-delayed feedback control, referred to as the intermittent control in this study, is one of the novel hypothetical neural strategies for stabilizing upright posture during quiet stance.[5,6,7] Intermittency and discontinuity in the action of nonlinear postural controllers have been well established in the literature.[5–18] recent studies are beginning to associate intermittency with a healthy control strategy and loss of intermittency with deterioration in postural function,[19,20] it is still controversial whether such time-discontinuous, nonlinear controllers are more physiologically plausible compared to the traditional time-continuous linear controllers, i.e., the stiffness and impedance controllers as models of healthy strategy for postural stabilization
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