Using virtual reality to explore the role of conflict resolution and environmental salience in Freezing of Gait in Parkinson's disease

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. Conclusion: 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.