Evaluating the Effect of Subthalamic Deep Brain Stimulation on Vocal Function in Parkinson’s Disease

The study reports the effect of subthalamic deep brain stimulation (STN DBS) on vocal function in Parkinson’s disease (PD). Specifically, the effect was evaluated in relation to the vibratory characteristics of the vocal folds during sustained vowel phonation using two different methods: one measures jitter and shimmer, while the other measures the correlation dimension D2, a nonlinear dynamic analysis. Twenty right-handed individuals with advanced PD and dysarthria underwent unilateral STN DBS. Ten were operated on the right hemisphere and ten on the left hemisphere. The side receiving STN DBS had more affected motor function. Speech was evaluated before surgery and three-to-six months after surgery with stimulator-off and with stimulator-on; all were off anti-Parkinsonian medication for 12 h before evaluation. Evaluators and subjects were blinded to the subjects stimulator status at the postsurgery evaluations. Nonspeech motor performance was assessed with UPDRS-III. Each subject produced six maximally sustained ‘‘ah’’ phonations (MSVPs) at his/her habitual loudness level. Two-second samples extracted from the MSVPs were used for both analyses. In addition, the maximum vocal intensity, duration, mean F0, and cycle-to-cycle F0 variation were also obtained. The results were discussed with regard to Chaos theory and the phonation characteristics in PD.