Effect of subthalamic nucleus or globus pallidus interna stimulation on oculomotor function in patients with parkinson's disease

Background: Deep brain stimulation (DBS) of either the globus pallidus interna (GPi) or subthalamic nucleus (STN) is similarly effective for treating somatomotor manifestations of Parkinson's disease (PD), but differences in how stimulation of each target affects oculomotor function are poorly understood. Objective: We sought to determine if stimulation of the STN, but not the GPi, affects oculomotor function in PD patients. Methods: Nineteen PD patients with DBS implants (8 bilateral GPi, 9 bilateral STN and 2 unilateral STN) were studied. Testing was performed with stimulation on, then off. Somatomotor function was tested using the Unified Parkinson's Disease Rating Scale (UPDRS) motor exam. For oculomotor testing, patients performed pro- and antisaccade tasks while monitored with an infrared eye tracker. Saccadic latency, saccadic intrusions, and square-wave jerks (SWJs) were measured for each trial. Results: As expected, UPDRS motor scores improved with both GPi and STN stimulation. With GPi stimulation, there was no significant difference in oculomotor function with stimulation on or off. However, with STN stimulation on, there was a significant increase in the mean number of SWJs/s, as well as a significant decrease in latency for both pro- and antisaccade tasks. Conclusion: Stimulation of either GPi or STN had similar effects on somatomotor function, but only STN stimulation significantly altered oculomotor function.