Laryngeal dystonia (LD) causes excessive vocal fold abduction (opening) or adduction (closing) leading to decreased voice quality, job prospects, self-worth and quality of life. Individuals with LD often experience episodic breathy voice, decreased ability to sustain vocal fold vibration, frequent pitch breaks and in some cases, vocal tremor. While neuroimaging investigations have uncovered both cortical organization and regional connectivity differences in structures in parietal, primary somatosensory and premotor cortices of those with LD, there remains a lack of understanding regarding how the brains of those with LD function to produce phonation and how these might differ from those without LD. Intervention options for people with LD are limited to general voice therapy techniques and Botulinum Toxin (Botox) injections to the posterior cricoarytenoid (PCA) and/or TA (thyroarytenoid) often bilaterally, to alleviate muscle spasms in the vocal folds. However, the effects of injections are short-lived, uncomfortable, and variable. To address this gap, the aim of this study is to investigate the effectiveness of repetitive transcranial magnetic stimulation (rTMS), a non-invasive neuromodulation technique, in assessing cortical excitability and inhibition of laryngeal musculature. Previous work conducted by the investigator has demonstrated decreased intracortical inhibition in those with adductor laryngeal dystonia (AdLD) compared to healthy controls. The investigators anticipate similar findings in individuals with with other forms of LD, where decreased cortical inhibition will likely be noted in the laryngeal motor cortex. Further, following low frequency (inhibitory) rTMS to the laryngeal motor brain area, it is anticipated that there will be a decrease in overactivation of the TA muscle. To test this hypothesis, a proof-of-concept, randomized study to down-regulate cortical motor signal to laryngeal muscles will be compared to those receiving an equal dose of sham rTMS. Previous research conducted by the investigator found that a single session of the proposed therapy produced positive phonatory changes in individuals with AdLD and justifies exploration in LD.
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Change in Objective Assessment of Phonatory Function
Timeframe: Day 1 (baseline), day 5 (post intervention), and Day 12 (follow up) timepoints for both arms of the study.
Change in Cortical Excitability (intrahemispheric inhibition)
Timeframe: Day 1 (baseline), Day 5 (post intervention)