Effects of deep brain stimulation of dorsal versus ventral subthalamic nucleus regions on gait and balance in Parkinson's disease

Abstract

Objective: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves motor function, including gait and stability, in people with Parkinson's disease (PD) but differences in DBS contact locations within the STN may contribute to variability in the degree of improvement. Based on anatomical connectivity, dorsal STN may be preferentially involved in motor function and ventral STN in cognitive function.

Methods: To determine whether dorsal DBS affects gait and balance more than ventral DBS, a double blind evaluation of 23 PD patients with bilateral STN DBS was conducted. Each participant underwent gait analysis and balance testing off Parkinson's medication under three DBS conditions (unilateral DBS in the dorsal STN region, unilateral DBS in the ventral STN region and both stimulators off) on 1 day.

Results: Improvements were seen in Unified Parkinson's Disease Rating Scale (UPDRS)-III scores and velocity in walking trials as fast as possible (Fast gait) and preferred pace (Pref gait), as well as stride length for Fast and Pref gait, with dorsal and ventral stimulation compared with the off condition (post hoc tests, p<0.05). However, there were no differences with dorsal compared to ventral stimulation. Balance, assessed using the multi-item mini-Balance Evaluation Systems Test (mini-BESTest), was similar across conditions.

Conclusions: Absence of differences in gait and balance between the dorsal and ventral conditions suggests motor connections involved in gait and balance may be more diffusely distributed in STN than previously thought, as opposed to neural connections involved in cognitive processes, such as response inhibition, which are more affected by ventral stimulation.

Figure 1

Contact locations for included participants. Coronal sections containing the STN (red outline) are shown anterior to posterior. All left side contacts used have been mirrored on the right side for ease of display. Spheres represent estimated 2 mm current spread around the dorsal (green) and ventral (purple) contact tip across subjects. Scale bar indicates the number of participants with overlapping spheres for that voxel.

Figure 2

Mean velocity and stride length for Fast and Pref gait for each stimulation condition. Fast velocity and Fast and Pref stride length were significantly higher with dorsal and ventral DBS, compared to off. Velocity for Pref gait was significantly different between dorsal DBS and off. There were no differences between dorsal DBS and ventral DBS. Mean values ± SEM. *p≤0.05, **p≤0.01, ***p≤0.001.

Figure 3

Total a) mini-BESTest and b) UPDRS-III scores were compared across conditions. Balance did not differ between conditions, but total UPDRS-III scores were significantly improved with dorsal and ventral DBS, compared to off. There were no differences between dorsal DBS and ventral DBS. Mean values ± SEM. ***p≤0.001.