No Effect of Different Stimulation Conditions on Verbal Fluency and Visuospatial Orientation in Patients with Subthalamic Nucleus Deep Brain Stimulation

Background: Subthalamic nucleus deep brain stimulation is an effective treatment for the symptomatic treatment of Parkinson's disease. Apart from the obvious motor benefits, some cognitive side effects have been reported, particularly in verbal fluency. Objectives: Our aim was to evaluate the effects of the stimulation on verbal fluency and visuospatial orientation with changing stimulation conditions in 35 patients with Parkinson's disease. Methods: Patients were randomized for their stimulation conditions as ‘both on', ‘both off', ‘right on', and ‘left on' and underwent verbal fluency and visuospatial orientation tasks during their drug-on periods. Letter and categorical fluency tasks and Benton's Judgment of Line Orientation Test were used for assessment. Results: Overall, 6 patients were excluded due to dementia or depression. For verbal fluency, the number of words they produced in 1 min was similar in four stimulation conditions (p > 0.05). No significant difference was found between stimulation conditions in the spatial orientation task. Conclusions: We were unable to find any significant changes in verbal fluency and visuospatial orientation task scores with different stimulation conditions. This result suggests that either stimulation has no effect on given domains or the effect is so small that more detailed batteries are required to detect the difference.