Journal of Alzheimers Disease & Parkinsonism
Open Access

Abstract

Postural instability is one of the cardinal signs of Parkinson�s disease (PD). Quantifying postural stability is commonly used to measure PD severity. We hypothesized that postural synergy indices in the space of activation of muscle groups (M-modes) may be used to measure changes in motor coordination due to PD and dopamine-replacement therapy. Synergy indices stabilizing the center of pressure (COP) were compared between 11 patients without clinical symptoms of postural instability (Hoehn-Yahr stage-II) and 11 age-matched controls, and between 10 patients (stage II and III) tested off-drug and on-drug. Electromyographic signals from 13 leg and trunk muscles, recorded during cyclic body sway and releasing a load from extended arms, were used to quantify synergy indices by comparing the variance that had no effect on the COP coordinate and the variance that changed COP coordinate. Since this analysis needs multiple trials to identify the variance structure, we also quantified components of motion in the space of M-modes that had (non-motor equivalent) and did not have effect (motor equivalent) on COP coordinate using individual sway cycles. PD patients showed significantly lower synergy indices, and reduced ability to adjust these indices in preparation to an action. Motor equivalence analysis confirmed these differences. Impaired ability to adjust synergy indices in preparation to an action may contribute to rigidity and episodes of freezing. We conclude that analysis of motor equivalence in muscle activation space, using a few trials, can be used as a clinical measure for early diagnosis of PD and tracking disease progression.

Biography

Email: auf14@psu.edu