Deep brain stimulation of subthalamic nucleus and caudal zona incerta in patients with Parkinson’s disease: A perceptual study of effects on articulatory precision

Abstract: Abstract Background Deep brain stimulation (DBS) is a viable surgical treatment method for Parkinson’s disease (PD). It has positive effects on the classical motor symptoms, but effects on speech and voice are not equally beneficial. The speech disorder related to PD is hypokinetic dysarthria, with impaired articulatory precision as a prominent symptom. Studies have shown effects on different aspects of speech due to DBS of the subthalamic nucleus (STN) but the effects of stimulation of the caudal zona incerta (cZi) are less explored. Aims The aim of the current study was to investigate the effect of STN-DBS and cZi-DBS on perceptually measured articulatory precision in PD patients. Method Read speech productions were collected from 19 DBS-treated PD patients, ten STN and nine cZi. The recordings were made before surgery and 12 months postoperatively with stimulator on and off. Levodopa medication was always on. From the reading passage, three-syllable words were selected and isolated. Articulatory precision of the words was rated in two different assessments; an overall rating of articulatory precision and an identification of occurring misarticulations. Results The results from the perceptual assessment showed a decrease in articulatory precision after surgery for both groups. The decrease was significant for the cZi group, but not for the STN group. There was no significant difference between the groups. The frequency of observed misarticulations increased as an effect of DBS for both patient groups, with significant increase for the STN group but not for the cZi group. There was no significant difference between the groups. The most commonly observed misarticulation categories were stop-plosive reduced in quality, fricative realized as other fricative and stop-plosive realized as fricative . Conclusions The results obtained in the current study show that STN-DBS and cZi-DBS may have adverse effects on articulatory precision in PD patients. Keywords Articulatory precision, Parkinson’s disease, DBS, STN, cZi