Discerning effect of cognitive capacity on dual task in Parkinson's disease and healthy controls

[Poster] Objective: To examine dual-task interference during gait using a cognitive task titrated to individual capacity. Background: Dual-task interference during gait is common in older adults and people with Parkinson's disease (PD), however the underlying processes are poorly understood and confounded by methodological differences which impact on test results. Methods: Baseline forward digit span (single task) was established over 2 minutes in 121 people with early PD and 189 older adults. Participants walked for two minutes at preferred pace under single and dual-task (forward digit span recall) conditions. Task demand was increased (forward digit span +1) in a subgroup (n = 55 control, n = 44 PD) to assess the impact of cognitive capacity on dual-task interference. We also examined task prioritisation of performance between gait and digit span under dual-task conditions. Partial correlations were used to test the relationship between dual-task interference and motor control (Postural Instability and Gait Disorder subscore of the UPDRS III), and cognitive function (global cognition, attention and executive function), controlling for order of dual-task presentation. Results: PD and controls responded similarly to dual-task for all gait characteristics except for step width and step width variability and this was the same when task demand increased (dual+1). Control participants took wider steps (p = .006) and step width variability increased significantly for controls (p = .001). Digit span error rates were not significantly different between groups during dual-task performance. There were no significant correlations with dual task interference and global cognition, motor deficit, and executive function for either group. Response to dual task was highly individual. Conclusions: The effects of dual-task on gait performance are two-fold and specific to the gait characteristic. For both PD and control they reflect an age related reduction in gait performance (especially forward progression), possibly due to reduced working memory capacity. Secondly, the results show that postural stability during walking in early PD is disproportionately affected. Further work is required to identify the cognitive, executive and motor correlates of dual-task interference from which inferences about underlying cognitive processes can be made