Objective: We aim to quantify the effects of VIM-DBS on speech regulation mechanisms in patients with Essential Tremor (ET).

Background: VIM-DBS is an effective treatment for medication-resistant patients with ET. However, patients report that stimulation has a deleterious effect on the speech. Acoustic studies on VIM-DBS in patients with MS (Puetzer et al. 2007) and ET (Muecke et al. 2014) have shown a deterioration of the oral speech motor system. In the acoustic domain, they found frication during closures, indicating an imprecise articulation. The present study directly investigates articulation by using Electromagnetic Articulography to capture stimulation-induced effects.

Methods: We recorded 12 ET patients with DBS-ON and DBS-OFF conditions and 12 controls. Patients had been bilateral implanted with VIM-DBS. An AG501 (sensors on lips, tongue tip and dorsum) was used to record a fast syllable repetition task, /pa/, /ta/, /ka/. Landmarks of the articulatory gestures were identified at zero-crossings in the velocity and acceleration traces to compute variables of a mass-spring model: stiffness, displacement, peak velocity, duration of acceleration and deceleration phases.

Results: Linear mixed models with DBS (ON, OFF), place (labial, alveolar, velar) and syllable position as predictors predictors (varying intercepts for subjects), revealed an interaction of DBS and place comparing controls vs. OFF: differences were strongest in the lingual/velar system (i.e. shrinking of /k/-gesture in OFF with p<0.0001 for acc., displ., vel., stiff.); in contrast /p/ and /t/ were hyperarticulated in OFF). Comparing ON vs OFF for the patients, we found a shrinking of all gestures (p<0.0001) entailing slower and smaller movements under stimulation. For stiffness, we found an interaction of DBS and place (p<0.0001): differences were strongest for tongue body articulation. Moreover, production in patients was more variable than in controls.

Conclusions: The results reveal stimulation-induced effects on regulation in speech motor control for ET patients. Patients in the OFF condition hyperarticulate syllables where closures of the lips and the tongue tip are required, but hypoarticulate (fail to reach the target) when the tongue body is involved. In comparison to the OFF condition, all gestures are hypoarticulated in the ON condition, whether lingual or labial, leading to less precise articulation.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/regulation-in-speech-motor-control-in-et-patients-treated-with-dbs-kinematics-of-the-lingual-and-the-labial-systems/