Kinematic effects of subthalamic stimulation on reach-to-grasp movements in Parkinson's disease

Background: Parkinsonian patients demonstrate particular difficulties when performing sequential motor tasks compared to simple movements indicating an important role of the basal ganglia in switching between different motor programs.

Objective: To investigate the impact of subthalamic stimulation on the kinematics of composed reach-to-grasp movements and on isolated movement segments.

Methods: 11 age matched controls and 16 PD patients with subthalamic stimulation were examined without medication with stimulation switched on and off. All subjects were instructed to perform three different externally cued hand movements: 1) The complete reach-to-grasp movement consisting of hand transport to and precision grip around a target. 2) The isolated reach movement to the grip device 3) The isolated precision grip and button press. Kinematic data were recorded with a 3D ultrasound movement analysis system (CMS 70 P4-V5, Zebris, Germany).

Results: The effect of subthalamic stimulation was accentuated during the reach phase compared to the grip formation during the composed movement. Stimulation induced kinematic changes of the composed movement were comparable to those of both isolated submovements.

Conclusion: Subthalamic stimulation improved certain aspects of all three hand movement types but did not differentially impact the composed reach-to-grasp task compared to the simple submovements. We assume that the complete reach-to-grasp task is encoded in a single generalised motor program which is affected by stimulation.