Long-term effects of thalamic deep brain stimulation on force control in a patient with Parkinson's disease-driven action tremor

It is well known that thalamic deep brain stimulation (DBS) in the ventral intermedius nucleus (VIM) reduces contralateral tremor. However, the ways in which VIM DBS alters force control in patients with Parkinson's disease (PD) are not currently known.The goal of this project was to characterize the effect of VIM DBS on force control of a tremor-dominant Parkinson's patient. The patient was evaluated before, and at 3, 6, and 13 months after surgery. The study task required independent, controlled application and release of force by the thumb and index finger to trace a template. Thalamic stimulation resulted in tremor reduction and improvement in force control of the contralateral (preferred) hand. However, differences in force control remained.When compared to a control subjects' preferred hand and to the ipsilateral (non-preferred) hand, the contralateral hand had a lower concordance phase value.This demonstrates a greater tendency for the changes in force trajectories to be in different directions in contrast to the same direction as is required to perform the task. In this PD patient, thalamic stimulation resulted in improvement in force control, although the control remains different than that exhibited by a control subject with no known neuropathology.