Objective: Identify whether muscle synergies are altered in stage I Parkinson’s disease (PD).

Background: Muscle synergies have been proposed as a mechanism utilized by the central nervous system (CNS) to reduce the computational load associated with the execution of voluntary movements. According to the action-selection model, the basal ganglia encode voluntary movement. Selecting appropriate muscle synergies for a given motor task may rely upon proper basal ganglia function.

Methods: We recorded EMGs from 16 upper-limb muscles during arm reaching in four patients with stage I PD and four healthy controls. We estimated the muscle synergies for each limb using the non-negative matrix factorization algorithm. We compared the limb-specific muscle synergies within the healthy controls and within the PD patients using the scalar-product similarity. Note that we refer to the "affected" and "unaffected" arm of patients with PD as it relates to the presence or not of clinical motor symptoms, respectively.

Results: Eight synergies were sufficient to adequately describe the EMGs for the controls and the “unaffected” arm of patients with PD. At the same number of synergies, the quality of the EMG reconstruction for the “affected” arm of patients with PD was poorer (p=0.08). This observation suggests more data complexity in the EMGs for the “affected” arm of patients with PD. Controls showed consistently similar synergies among themselves. Muscle synergies in patients with PD exhibited lower intra-group similarity for both the “affected” (p=0.01) and “unaffected” arm (p=0.06) when compared to the intra-group similarity of controls.

Conclusions: Our results suggest a possible relationship between muscle synergies and basal ganglia function. They are in line with evidence of asymmetrical degeneration in the basal ganglia in PD. Importantly, the set of upper-limb muscle synergies may be a sensitive measure that displays alterations prior to the appearance of clinical motor symptoms.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/alterations-in-muscle-synergies-in-early-stage-parkinsons-disease/