title: Dopaminergic modulation of multi-muscle synergies in postural tasks performed by patients with Parkinson's disease.
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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Falaki
authors.affiliation: 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.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Huang
authors.affiliation: 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.
authors.forename: Mechelle M
authors.initials: MM
authors.lastname: Lewis
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA. Electronic address: mll11@psu.edu.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Latash
mesh_terms: D000328:Adult; D000368:Aged; D015259:Dopamine Agents / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007980:Levodopa / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D010300:Parkinson Disease / Q000188:drug therapy / Q000503:physiopathology*; D004856:Postural Balance / Q000187:drug effects*; D011187:Posture
chemical_list: D015259:Dopamine Agents; D007980:Levodopa
keywords: Anticipatory synergy adjustments; Dopaminergic medication; Muscle mode; Parkinson’s disease; Posture; Synergy