Abstract
Purpose. To investigate changes in vowel articulation with the electrical deep brain stimulation (DBS) of the subthalamic nucleus (STN) in dysarthric speakers with Parkinson's disease (PD). Methods. Eight Quebec-French speakers diagnosed with idiopathic PD who had undergone STN DBS were evaluated ON-stimulation and OFF-stimulation (1 hour after DBS was turned off). Vowel articulation was compared ON-simulation versus OFF-stimulation using acoustic vowel space and formant centralization ratio, calculated with the first (F1) and second formant (F2) of the vowels /i/, /u/, and /a/. The impact of the preceding consonant context on articulation, which represents a measure of coarticulation, was also analyzed as a function of the stimulation state. Results. Maximum vowel articulation increased during ON-stimulation. Analyses also indicate that vowel articulation was modulated by the consonant context but this relationship did not change with STN DBS. Conclusions. Results suggest that STN DBS may improve articulation in dysarthric speakers with PD, in terms of range of movement. Optimization of the electrical parameters for each patient is important and may lead to improvement in speech fine motor control. However, the impact on overall speech intelligibility may still be small. Clinical considerations are discussed and new research avenues are suggested.
Highlights
Parkinson’s disease (PD) has traditionally been considered strictly as a motor disorder with symptoms such as tremor, muscle rigidity, and bradykinesia
Even though our results indicate that this type of coarticulation is not sensitive to subthalamic nucleus (STN) deep brain stimulation (DBS), the impact of the stimulation on speech coarticulation should be explored in future studies because (1) it has been shown to be altered in some studies on dysarthria in PD [26] and (2) it is essential to speech intelligibility [47]
This study is one of the first to investigate changes in vowel articulation and coarticulation that occur with STN DBS in PD in terms of maximum range
Summary
Parkinson’s disease (PD) has traditionally been considered strictly as a motor disorder with symptoms such as tremor, muscle rigidity, and bradykinesia. Studies examining physiological changes in the speech systems of people with PD reported impaired respiratory [3], laryngeal [4], and orofacial [5, 6] functions which have an impact on the acoustic signal of speech. Studies investigating such changes reported reduced intensity level [7] and fundamental frequency (f0) range [8], altered phonation quality [9], and inaccurate and reduced articulation [10,11,12]. As a result, impaired intelligibility is very common in PD [13]
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