Background/Aims: Deep brain stimulation (DBS) is widely used to treat motor symptoms in patients with advanced Parkinson’s disease. The aim of this study was to investigate the anatomical aspects of the electric field in relation to effects on speech and movement during DBS in the subthalamic nucleus. Methods: Patient-specific finite element models of DBS were developed for simulation of the electric field in 10 patients. In each patient, speech intelligibility and movement were assessed during 2 electrical settings, i.e. 4 V (high) and 2 V (low). The electric field was simulated for each electrical setting. Results: Movement was improved in all patients for both high and low electrical settings. In general, high-amplitude stimulation was more consistent in improving the motor scores than low-amplitude stimulation. In 6 cases, speech intelligibility was impaired during high-amplitude electrical settings. Stimulation of part of the fasciculus cerebellothalamicus from electrodes positioned medial and/or posterior to the center of the subthalamic nucleus was recognized as a possible cause of the stimulation-induced dysarthria. Conclusion: Special attention to stimulation-induced speech impairments should be taken in cases when active electrodes are positioned medial and/or posterior to the center of the subthalamic nucleus.
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