title: Impaired visuospatial transformation but intact sequence processing in Parkinson disease.
abstract: OBJECTIVE
  We examined whether visuospatial deficits in Parkinson disease (PD) can be explained by a domain-general, nonspatial impairment in the sequencing or serial chaining of mental operations.
  
  
  BACKGROUND
  PD has been shown to be associated with impaired visuospatial processing, but the mechanisms of this impairment remain unclear.
  
  
  METHODS
  Thirteen patients with PD and 20 age-matched, neurologically normal controls performed a visuospatial grid navigation task requiring sequential spatial transformations. The participants also performed a control task of serial number subtraction designed to assess their nonvisuospatial sequencing. The tasks were matched in structure and difficulty.
  
  
  RESULTS
  The patients were impaired on the visuospatial task but not in serial number subtraction. This finding suggests that visuospatial processing impairments in PD do not derive from a general impairment affecting sequencing or serial chaining.
  
  
  CONCLUSIONS
  We argue that visuospatial deficits in PD result from impairments to spatial transformation routines involved in the computation of mappings between spatial locations. These routines are mediated by dopaminergic pathways linking the basal ganglia, prefrontal cortex, supplementary motor area, and parietal cortex.
authors.affiliation: *Wolfson Centre for Clinical and Cognitive Neuroscience, School of Psychology ‡School of Medical Sciences, Bangor University, Bangor, United Kingdom †Department of Psychology, Swansea University, Swansea, United Kingdom.
authors.forename: E Charles
authors.initials: EC
authors.lastname: Leek
authors.forename: Julie H
authors.initials: JH
authors.lastname: Kerai
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Johnston
authors.forename: John V
authors.initials: JV
authors.lastname: Hindle
authors.forename: R Martyn
authors.initials: RM
authors.lastname: Bracewell
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001479:Basal Ganglia / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term; D008875:Middle Aged; D009044:Motor Cortex / Q000378:metabolism; D009483:Neuropsychological Tests; D010296:Parietal Lobe / Q000378:metabolism; D010300:Parkinson Disease / Q000378:metabolism / Q000503:physiopathology / Q000523:psychology*; D010364:Pattern Recognition, Visual; D017397:Prefrontal Cortex / Q000378:metabolism; D011597:Psychomotor Performance; D015398:Signal Transduction; D013028:Space Perception; D013850:Thinking; D006113:United Kingdom
chemical_list: D004298:Dopamine