Anxiety-provoked gait changes are selectively dopa-responsive in Parkinson's disease.
In order to understand how dopamine modulates the effect of anxiety on gait, the goal of this study was to use virtual reality to provoke anxiety in Parkinson's disease (PD) (in both ON and OFF states) and quantify its effect on gait. Seventeen participants with PD and 20 healthy age-matched controls were instructed to walk in a virtual environment in two anxiety-provoking conditions: (i) across a plank that was located on the GROUND and (ii) across an ELEVATED plank. All participants with PD completed this experiment in both the ON and OFF states, and were then striated into groups based on baseline trait anxiety scores for further analyses. Anxiety (skin conductance and self-report) and spatiotemporal aspects of gait were measured. Overall, the ELEVATED condition resulted in greater skin conductance levels and self-reported anxiety levels. Additionally, all participants demonstrated slower gait with increased step-to-step variability when crossing the ELEVATED plank compared with the plank on the GROUND. The results showed that dopaminergic treatment selectively improved gait in only the highly anxious PD group, by significantly improving velocity, step length, step time and step-to-step variability specifically when walking across the ELEVATED plank (ON vs. OFF comparison). In conclusion, only highly trait anxious participants with PD benefitted from dopaminergic treatment, specifically when walking in the anxiety-provoking environment. Improvements to gait during anxious walking might be a result of dopaminergic medication acting in two ways: (i) improving the basal ganglia's capacity to process information and (ii) reducing the load from anxiety and subsequently making more resources available to effectively process other competing inputs.