An investigation of the effects of subthalamic nucleus stimulation on acoustic measures of voice.

Seven patients with Parkinson's disease were implanted with deep brain stimulators to provide chronic electrical stimulation to the subthalamic nucleus bilaterally. Acoustic recordings and neurologic assessments were undertaken before surgery in the medication-off and medication-on conditions and after surgery with and without electrical stimulation in the medication-off and medication-on conditions. The data showed significant improvements in limb motor performance in response to medication before surgery and when the subthalamic nucleus was stimulated after surgery. Six months after surgery, there were small but statistically significant increases in sound pressure level and fundamental frequency variability in response to stimulation in the medication-on condition. No other statistically significant speech changes were measured. These findings are consistent with several other studies that have reported disparity between limb and speech improvements after neurosurgical intervention for Parkinson's disease.