Unilateral vs. bilateral STN DBS effects on working memory and motor function in Parkinson disease

Abstract

Bilateral subthalamic nucleus deep brain stimulation (STN DBS) can reduce working memory while improving motor function in Parkinson disease (PD), but findings are variable. One possible explanation for this variability is that the effects of bilateral STN DBS on working memory function depend in part on functional or disease asymmetry. The goal of this study was to determine the relative contributions of unilateral DBS to the effects seen with bilateral DBS. Motor (Unified Parkinson Disease Rating Scale Part III, UPDRS) and working memory function (Spatial Delayed Response, SDR) were measured in 49 PD patients with bilateral STN DBS while stimulators were Both-off, Left-on, Right-on and Both-on in a randomized, double-blind manner. Patients were off PD medications overnight. Effects of unilateral DBS were compared to effects of bilateral STN DBS. Mean UPDRS and SDR responses to Left-on vs. Right-on conditions did not differ (p>.20). However, improvement in contralateral UPDRS was greater and SDR performance was more impaired by unilateral DBS in the more affected side of the brain than in the less affected side of the brain (p=.008). The effect of unilateral DBS on the more affected side on contralateral UPDRS and SDR responses was equivalent to that of bilateral DBS. These results suggest that motor and working memory function respond to unilateral STN DBS differentially depending on the asymmetry of motor symptoms.

Figure 1. Effects of unilateral and bilateral STN DBS on motor function by group

Mean (±SEM) percent change in motor scale score (UPDRS) with unilateral stimulation compared to Both-off condition. Positive values indicate worsening with stimulation; negative values indicate improvement with stimulation. There was a significant interaction between stimulation condition and group for both motor function (p=.03).

Figure 2. Effects of unilateral and bilateral STN DBS working memory performance by group

Mean (±SEM) percent change in working memory performance (SDR) with unilateral stimulation compared to Both Off condition. Positive values indicate worsening with stimulation; negative values indicate improvement with stimulation. There was a significant interaction between stimulation condition and group for SDR performance (p=.03).

Figure 3

Effects of stimulation on the more affected and less affected sides of the brain compared to bilateral stimulation. Mean (±SEM) percent change in working memory performance (SDR) and motor function (UPDRS) with unilateral stimulation compared to Both-off condition. Positive values indicate worsening with stimulation; negative values indicate improvement with stimulation. Stimulation on the more affected side of the brain was associated with significantly greater decrement in working memory performance and significantly greater improvement in motor function compared to stimulation on the less affected side of the brain. * Different from Both On condition, p<.05; ** Different from less affected side condition, p<.05.