Objective: We investigate the effect of VIM-DBS on speech production in patients with ET.

Background: Dysarthria is a common side effect of VIM-DBS. In recent studies, we used acoustic parameters to show deterioration in speech of ET patients under stimulation. We found changes in the glottal and oral systems while DBS is on, specifically an increase of voicing during the entire syllable cycle as well as frication during the consonantal constriction, indicating a reduced degree of glottal abduction and an imprecise oral articulation.

Methods: 12 German ET patients and 12 age- and sex-matched healthy control-speakers were included into the study. Each participant was recorded with an Electromagnetic Articulograph (AG501) and a time-synchronized acoustic signal with DBS-on and DBS-off. To capture oral articulation, sensors were placed at the tongue tip, tongue dorsum, jaw and lips. Speech materials included fast-syllable repetition tasks of consonant-vowel sequences (/papapa/, /tatata/, /kakaka/). Measures in the acoustic waveform included syllable duration as well as the amount of voicing and frication during the consonantal closure. Measures in the kinematic domain included displacement, duration of acceleration and deceleration phases, peak velocity and stiffness of the opening and closing gestures during the production of the consonant-vowel sequences.

Results: Acoustic parameters confirmed our previous findings. Articulographic analysis revealed significant effects of stimulation on the lip and the tongue movements during the consonantal production. Under stimulation, we found considerably longer acceleration phases (increase of 49ms) and deceleration phases (increase of 59ms), lower peak velocities (decrease of 20mm/sec), smaller displacements (reduction of 0.7mm) and lower stiffness of the articulators natural frequency.

Conclusions: Under DBS, movements of the labial and lingual systems are longer in duration, slower in peak velocity, smaller in displacement and less stiff in terms of natural frequency, leading to incomplete closures in the production of stop consonants /p,t,k/, making the speech sound slurred. This is the first time that effects of stimulation on the speech motor system can be quantified in terms of kinematic parameters of the lingual and labial system responsible for articulatory imprecision.

Presented partially at MDS Congress San Diego and during Dymo Workshop 2015 Cologne.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/articulography-reveals-disturbed-speech-motor-control-in-et-patients-treated-with-vim-dbs/