Deep Brain Stimulation (DBS) of the subthalamic nucleus (STN) is now widely used to alleviate symptoms of Parkinson's disease (PD). The long-term goal is to develop a quantitative tool to facilitate selection of DBS settings in the clinic since the typical parameter selection process may not adequately consider the effects of DBS on posture control. The aim of this study was to characterize the effects of changing the stimulation amplitude of DBS on posture control in PD. A dynamic posture shift paradigm involving target acquisition was used to assess posture control in 4 PD STN-DBS subjects. Each subject was tested at 4 stimulation amplitude settings: Clinically-determined (CD) settings, moderate (approx. 70% CD), low (approx. 30% CD), and off (no stimulation). Movements of the center of pressure and the position of the pelvis were monitored and several quantitative indices were calculated. The most substantial change was reductions in the peak velocity and the average movement velocity during the initial and mid phases of movement towards the target posture. These results may be explained in terms of increased akinesia and bradykinesia in the altered stimulation conditions. Thus, the dynamic posture shift paradigm can reveal changes in posture control capabilities, as evidenced by changes in movement velocity, due to alterations in DBS stimulation settings.
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