title: First trial reactions and habituation rates over successive balance perturbations in Parkinson's disease.
abstract: BACKGROUND
  Balance control in Parkinson's disease is often studied using dynamic posturography, typically with serial identical balance perturbations. Because subjects can learn from the first trial, the magnitude of balance reactions rapidly habituates during subsequent trials. Changes in this habituation rate might yield a clinically useful marker. We studied balance reactions in Parkinson's disease using posturography, specifically focusing on the responses to the first, fully unpractised balance disturbance, and on the subsequent habituation rates.
  
  
  METHODS
  Eight Parkinson patients and eight age- and gender-matched controls received eight consecutive toe-up rotations of a support-surface. Balance reactions were measured with a motion analysis system and converted to centre of mass displacements (primary outcome).
  
  
  RESULTS
  Mean centre of mass displacement during the first trial was 51% greater in patients than controls (P=0.019), due to excessive trunk flexion and greater ankle plantar-flexion. However, habituated trials were comparable in both groups. Patients also habituated slower: controls were fully habituated at trial 2, whereas habituation in patients required up to five trials (P=0.004). The number of near-falls during the first trial was significantly correlated with centre of mass displacement during the first trial and with habituation rate.
  
  
  CONCLUSIONS
  Higher first trial reactions and a slow habituation rate discriminated Parkinson's patients from controls, but habituated trials did not. Further work should demonstrate whether this also applies to clinical balance tests, such as the pull test, and whether repeated delivery of such tests offers better diagnostic value for evaluating fall risks in parkinsonian patients.
authors.affiliation: Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: W
authors.initials: W
authors.lastname: Nanhoe-Mahabier
authors.forename: J H J
authors.initials: JH
authors.lastname: Allum
authors.forename: S
authors.initials: S
authors.lastname: Overeem
authors.forename: G F
authors.initials: GF
authors.lastname: Borm
authors.forename: L B
authors.initials: LB
authors.lastname: Oude Nijhuis
authors.forename: B R
authors.initials: BR
authors.lastname: Bloem
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*