The effects of subthalamic nucleus deep brain stimulation on vocal tract dynamics in Parkinson's disease

By S. Barlow, S. Park, M. Hammer, R. Pahwa, and S. Dascalos

An early observation associated with therapeutic ablative neurosurgery (i.e., palladotomy) was that electrical stimulation of the anatomic targets resulted in the same clinical effects as lesioning. Chronic high-frequency stimulation of the globus pallidus using an implanted electrode and pacemaker in patients with PD resulted in significant improvement in all subscales of the Unified Parkinson Disease Rating Scale without the adverse effects often associated with pallidotomy (brain ablation) (Pahwa et al., 1997). However, the precise effects of electrode location and parameters of deep brain stimulation on speech, vocalization, and other skills involving respiratory/vocal tract muscle systems remains unknown. In the current study, quantitative measures of vocal tract dynamics including speech aerodynamics, and orofacial force dynamics were sampled in a group of adult subjects with advanced Parkinson’s disease who also received deep brain stimulator (DBS) implants in the subthalamic nucleus (STN). In a number of individual cases, significant changes in motor control and reorganization of vocal tract dynamics were observed following bilateral DBS proximal to the STN. Electrical stimulation of the STN is generally thought to decrease or inhibit its output. The changes found in motor control of the vocal tract will be discussed in relation to what is currently known about the functional role of the subthalamic nucleus in sensorimotor control of speech and voice production.