Impact of sub-thalamic nucleus deep brain stimulation on dual tasking gait in Parkinson's disease

Background: The beneficial effects of bilateral sub-thalamic nucleus deep brain stimulation on motor function and gait in advanced Parkinson's disease are established. Less is known about the effect of stimulation on cognitive function and the capacity to walk while dual tasking, an ability that has been related to fall risk. Everyday walking takes place in complex environments that often require multi-tasking. Hence, dual tasking gait performance reflects everyday ambulation as well as gait automaticity. The purpose of this study was to examine the impact of subthalamic nucleus deep brain stimulation on dual task walking in patients with advanced Parkinson's disease. Methods: Gait was assessed using a performance-based test and by quantifying single-task and dual task walking conditions in 28 patients with advanced Parkinson's disease. These tests were conducted in 4 conditions: "OFF" medication, with the stimulator turned on and off, and "ON" medication, with the stimulator turned on and off. A previously validated, computerized neuro-psychological battery assessed executive function, attention and memory "OFF" and "ON" deep brain stimulation, after subjects took their anti-Parkinsonian medications. Results: Stimulation improved motor function and the spatiotemporal parameters of gait (e.g., gait speed) during both single-task and dual task walking conditions. Attention improved, but executive function did not. The dual task effect on gait did not change in response to stimulation. For example, during serial 3 subtractions, gait speed was reduced by -0.20 +/- 0.14 m/sec while OFF DBS and OFF meds and by -0.22 +/- 0.14 m/sec when the DBS was turned on (p = 0.648). Similarly, ON medication, serial 3 subtractions reduced gait speed by -0.20 +/- 0.16 m/sec OFF DBS and by -0.22 +/- 0.09 m/sec ON DBS (p = 0.543). Conclusions: Bilateral sub-thalamic nucleus deep brain stimulation improves motor symptoms, certain features of gait and even some aspects of cognitive function. However, stimulation apparently fails to reduce the negative impact of a dual task on walking abilities. These findings provide new insight into the effects of deep brain stimulation on gait during cognitively challenging conditions and everyday walking.