Purpose: The purpose of the present study was to examine the effect of deep brain stimulation (DBS) of the subthalamic nucleus (STN) and the caudal zona incerta (cZi) pitch characteristics of connected speech in patients with Parkinson's disease (PD).
Method: The authors evaluated 16 patients preoperatively and 12 months after DBS surgery. Eight patients were implanted in the STN (ages 51-72 years; M = 63 years). Six received bilateral implantation and 2 unilateral (left) implantation. Eight patients were bilaterally implanted in the cZi (ages 49-71 years; M = 60.8 years). Preoperative assessments were made after a levodopa challenge (approximately 1.5 times the ordinary dose). All postoperative examinations were made off and on stimulation with a clinically optimized dose of levodopa. Measurements of pitch range and variability were obtained from each utterance in a recorded read speech passage.
Results: Pitch range and coefficient of variation showed an increase in patients under STN-DBS. Patients under cZi-DBS showed no significant effects of treatment on investigated pitch properties.
Conclusion: STN-DBS was shown to increase pitch variation and range. The results provided no evidence of cZi-DBS having a beneficial effect on PD patients' pitch variability.