title: Characterising Upper Limb Movements in Huntington's Disease and the Impact of Restricted Visual Cues.
abstract: BACKGROUND
  Voluntary motor deficits are a common feature in Huntington's disease (HD), characterised by movement slowing and performance inaccuracies. This deficit may be exacerbated when visual cues are restricted.
  
  
  OBJECTIVE
  To characterize the upper limb motor profile in HD with various levels of difficulty, with and without visual targets.
  
  
  METHODS
  Nine premanifest HD (pre-HD), nine early symptomatic HD (symp-HD) and nine matched controls completed a motor task incorporating Fitts' law, a model of human movement enabling the quantification of movement timing, via the manipulation of task difficulty (i.e., target size, and distance between targets). The task required participants to make reciprocal movements under cued and blind conditions. Dwell times (time stationary between movements), speed, accuracy and variability of movements were compared between groups.
  
  
  RESULTS
  Symp-HD showed significantly prolonged and less consistent movement times, compared with controls and pre-HD. Furthermore, movement planning and online control were significantly impaired in symp-HD, compared with controls and pre-HD, evidenced by prolonged dwell times and deceleration times. Speed and accuracy were comparable across groups, suggesting that group differences observed in movement time, variability, dwell time and deceleration time were evident over and above simple performance measures. The presence of cues resulted in greater movement time variability in symp-HD, compared with pre-HD and controls, suggesting that the deficit in movement consistency manifested only in response to targeted movements.
  
  
  CONCLUSIONS
  Collectively, these findings provide evidence of a deficiency in both motor planning, particularly in relation to movement timing and online control, which became exacerbated as a function of task difficulty during symp-HD stages. These variables may provide a more sensitive measure of motor dysfunction than speed and/or accuracy alone in symp-HD.
authors.affiliation: School of Psychological Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Jessica
authors.initials: J
authors.lastname: Despard
authors.affiliation: School of Psychological Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Ternes
authors.affiliation: School of Psychological Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Bleydy
authors.initials: B
authors.lastname: Dimech-Betancourt
authors.affiliation: School of Psychological Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, Australia; Monash Biomedical Imaging, Monash University, Melbourne, Victoria, Australia; Victorian Life Sciences Computation Initiative, Life Sciences Computation Centre, Melbourne, Victoria, Australia.
authors.forename: Govinda
authors.initials: G
authors.lastname: Poudel
authors.affiliation: Department of Neurology, Monash Medical Centre, Clayton, Victoria, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Churchyard
authors.affiliation: School of Psychological Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Nellie
authors.initials: N
authors.lastname: Georgiou-Karistianis
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D006816:Huntington Disease / Q000175:diagnosis / Q000503:physiopathology*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D018911:Trinucleotide Repeats; D034941:Upper Extremity / Q000503:physiopathology*