Ali Falaki1, Xuemei Huang2, Mechelle M Lewis3, Mark L Latash4. 1. Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA. 2. Department of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Pharmacology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Radiology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Neurosurgery, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA. 3. Department of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Pharmacology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA. 4. Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA. Electronic address: mll11@psu.edu.
Abstract
BACKGROUND: Postural instability is one of most disabling motor symptoms in Parkinson's disease. Indices of multi-muscle synergies are new measurements of postural stability. OBJECTIVES: We explored the effects of dopamine-replacement drugs on multi-muscle synergies stabilizing center of pressure coordinate and their adjustments prior to a self-triggered perturbation in patients with Parkinson's disease. We hypothesized that both synergy indices and synergy adjustments would be improved on dopaminergic drugs. METHODS: Patients at Hoehn-Yahr stages II and III performed whole-body tasks both off- and on-drugs while standing. Muscle modes were identified as factors in the muscle activation space. Synergy indices stabilizing center of pressure in the anterior-posterior direction were quantified in the muscle mode space during a load-release task. RESULTS: Dopamine-replacement drugs led to more consistent organization of muscles in stable groups (muscle modes). On-drugs patients showed larger indices of synergies and anticipatory synergy adjustments. In contrast, no medication effects were seen on anticipatory postural adjustments or other performance indices. CONCLUSIONS: Dopamine-replacement drugs lead to significant changes in characteristics of multi-muscle synergies in Parkinson's disease. Studies of synergies may provide a biomarker sensitive to problems with postural stability and agility and to efficacy of dopamine-replacement therapy.
BACKGROUND: Postural instability is one of most disabling motor symptoms in Parkinson's disease. Indices of multi-muscle synergies are new measurements of postural stability. OBJECTIVES: We explored the effects of dopamine-replacement drugs on multi-muscle synergies stabilizing center of pressure coordinate and their adjustments prior to a self-triggered perturbation in patients with Parkinson's disease. We hypothesized that both synergy indices and synergy adjustments would be improved on dopaminergic drugs. METHODS:Patients at Hoehn-Yahr stages II and III performed whole-body tasks both off- and on-drugs while standing. Muscle modes were identified as factors in the muscle activation space. Synergy indices stabilizing center of pressure in the anterior-posterior direction were quantified in the muscle mode space during a load-release task. RESULTS:Dopamine-replacement drugs led to more consistent organization of muscles in stable groups (muscle modes). On-drugs patients showed larger indices of synergies and anticipatory synergy adjustments. In contrast, no medication effects were seen on anticipatory postural adjustments or other performance indices. CONCLUSIONS:Dopamine-replacement drugs lead to significant changes in characteristics of multi-muscle synergies in Parkinson's disease. Studies of synergies may provide a biomarker sensitive to problems with postural stability and agility and to efficacy of dopamine-replacement therapy.
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