Control of phonatory onset and offset in Parkinson patients following deep brain stimulation of the subthalamic nucleus and caudal zona incerta

Abstract

Laryngeal hypokinesia is a common symptom in Parkinson's disease (PD) that affects quality of life. Deep brain stimulation (DBS) is well recognized as a complementary method for treatment of motor symptoms in PD but the outcomes on patients' control over phonatory alternation have yet not been clearly elucidated. The present study examined the effect of subthalamic nucleus STN-DBS (n = 8, aged 51-72 yrs; median = 63 yrs) and caudal Zona incerta cZi-DBS (n = 8, aged 49-71 yrs; median = 61 yrs) on control of onset and offset of phonation in connected speech. The patients were evaluated in a preoperatively (Med ON, 1.5 times the ordinary Levodopa dose) and 12 months post-operatively (Med ON, ordinary Levodopa dose). The results provided evidence of a progressive reduction in the ability to manifest alternations between voicing and voiceless states in a reading task. Mean proportion produced with inappropriate voicing increased from 47.6% to 55.3% and from 62.9% to 68.6% of the total duration for the two groups of patients between Pre-op and Post-op, Stim OFF evaluations. The medial and final parts of the fricative were more affected than the initial part, indicating an increased voicing lead into the following vowel. We propose that this reduction in phonatory control is be due to either progression of the disease, an effect of reduced Levodopa dosage or a microlesional effect. Patients' proficiency in alternating between voiced and voiceless states in connected speech remained unaffected by both STN-DBS and cZi-DBS.