The persistent effects of unilateral pallidal and subthalamic deep brain stimulation on force control in advanced Parkinson's patients

Abstract

The persistent effects of unilateral deep brain stimulation (DBS) of the globus pallidus interna (GPi) or subthalamic nucleus (STN) on specific movement parameters produced by Parkinson's disease (PD) patients are poorly understood. The aim of this study was to determine the effects of unilateral GPi and STN DBS on the force-producing capabilities of PD patients during maximal efforts and functional bimanual dexterity. Clinical and biomechanical data were collected from 14 unilaterally implanted patients (GPi=7; STN=7), at least 13 months post-DBS surgery, during On and Off stimulation in the absence of medication. Unilateral DBS of either location produced a 33% improvement in UPDRS motor scores. Significant gains in maximum force production were present in both limbs during unimanual efforts. The greatest increase in maximum force, for both limbs, was under bimanual conditions. Force in the contralateral limb increased more than 30% during bimanual efforts while ipsilateral force increased by 25%. Unilateral DBS improved grasping force control and consistency of digit placement during the performance of a bimanual dexterity task. The clinical and biomechanical data indicate that unilateral DBS of GPi or STN results in persistent improvements in the control and coordination of grasping forces during maximal efforts and functional dexterous actions. Unilateral DBS implantation of either site should be considered an option for those patients in which bilateral procedures are contraindicated.

Figure 1

Illustration of bimanual dexterity paradigm used to assess functional motor performance.

Figure 2

The average percent change in maximum grip force produced by each limb during unimanual and bimanual testing from Off to On stimulation.

Figure 3

The summed force produced by each hand during unimanual (left + right during separate unimanual efforts)and bimanual (left + right during simultaneous efforts)conditions for both groups while off (upper plots) and on (lower plots) stimulation. Negative numbers above bars indicate a bilateral deficit while the positive value represents a bilateral facilitation.

Figure 4

Center of pressure (COP) values for all bimanual dexterity trials for both groups while Off and On DBS. The object area, outer circle of radius 2 cm, is divided into sectors of 30 degrees (dotted lines) in counter clock wise direction. The inner circle (gray dotted line) indicates the sub area of 1 cm radius. COP data is represented by stars and the solid ellipse defines the area of the spread to encompass 95 percent of the data.