title: Using virtual reality to explore the role of conflict resolution and environmental salience in freezing of gait in Parkinson's disease.
abstract: BACKGROUND
  The freezing phenomenon is among the most disabling symptoms of Parkinson's disease (PD) manifesting most commonly as Freezing of Gait with a paroxysmal cessation of effective stepping. Recent studies have suggested that freezing is related to both impairments in conflict resolution as well as the processing of environmentally salient information.
  
  
  METHODS
  In this study, we utilized a virtual reality gait paradigm to investigate differences in motor outflow between PD patients with (n = 36) and without (n = 37) Freezing of Gait, as well as age-matched healthy controls (n = 18). Subjects were required to navigate a realistic on-screen environment with the use of foot pedals to simulate stepping whilst responding to either cues associated with conflict resolution (congruent 'Red', 'Green' or 'Blue') or environmental salience (wide, narrow and sliding doorways). Footstep latency was used as a measure of motor output.
  
  
  RESULTS
  Significantly increased stepping latencies were observed in freezers compared to non-freezers (p = 0.004) and controls (p = 0.016) in response to stimuli requiring the inhibition of implicitly cued behavior ('red' cue). Patients with Freezing of Gait also demonstrated increased motor latency compared to non-freezers and controls specifically in response to environmentally salient triggers including narrow doorways (p = 0.03 and 0.01 respectively) and the opening of a sliding door (p = 0.036 and 0.048 respectively). Performance on the paradigm in relation to these triggers correlated significantly with self-reported freezing severity.
  
  
  CONCLUSIONS
  These results suggest that deficits in conflict resolution and visuospatial processing may reflect some of the neural mechanisms associated with freezing behavior and that these can be probed in a virtual reality environment.
authors.affiliation: Parkinson's Disease Research Clinic, Brain and Mind Research Institute, University of Sydney, Level 4, Building F, 94 Mallett St, Camperdown, New South Wales 2050, Australia.
authors.forename: Elie
authors.initials: E
authors.lastname: Matar
authors.forename: James M
authors.initials: JM
authors.lastname: Shine
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Naismith
authors.forename: Simon J G
authors.initials: SJ
authors.lastname: Lewis
mesh_terms: D000368:Aged; D004777:Environment; D005260:Female; D020233:Gait Disorders, Neurologic / Q000175:diagnosis / Q000523:psychology / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017008:Negotiating / Q000379:methods* / Q000523:psychology; D010300:Parkinson Disease / Q000175:diagnosis / Q000523:psychology / Q000628:therapy*; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D013037:Spatial Behavior / Q000502:physiology; D063367:Virtual Reality Exposure Therapy / Q000379:methods*
keywords: Conflict resolution; Environmental salience; Freezing of Gait; Parkinson's disease; Virtual reality; Visuospatial processing