Central voice production and pathophysiology of spasmodic dysphonia

Central Autonomic Mechanisms Involved in the Control of Laryngeal Activity and Vocalization

In humans, speech is a complex process that requires the coordinated involvement of various components of the phonatory system, which are monitored by the central nervous system. The larynx in particular plays a crucial role, as it enables the vocal folds to meet and converts the exhaled air from our lungs into audible sounds. Voice production requires precise and sustained exhalation, which generates an air pressure/flow that creates the pressure in the glottis required for voice production. Voluntary vocal production begins in the laryngeal motor cortex (LMC), a structure found in all mammals, although the specific location in the cortex varies in humans. The LMC interfaces with various structures of the central autonomic network associated with cardiorespiratory regulation to allow the perfect coordination between breathing and vocalization. The main subcortical structure involved in this relationship is the mesencephalic periaqueductal grey matter (PAG). The PAG is the perfect link to the autonomic pontomedullary structures such as the parabrachial complex (PBc), the Kölliker-Fuse nucleus (KF), the nucleus tractus solitarius (NTS), and the nucleus retroambiguus (nRA), which modulate cardiovascular autonomic function activity in the vasomotor centers and respiratory activity at the level of the generators of the laryngeal-respiratory motor patterns that are essential for vocalization. These cores of autonomic structures are not only involved in the generation and modulation of cardiorespiratory responses to various stressors but also help to shape the cardiorespiratory motor patterns that are important for vocal production. Clinical studies show increased activity in the central circuits responsible for vocalization in certain speech disorders, such as spasmodic dysphonia because of laryngeal dystonia.

The Effect of Rating Method on Reliability of Judgments of Strain Across Populations

PURPOSE

Variability in auditory-perceptual ratings of voice limits their utility, with the poorest reliability often noted for vocal strain. The purpose of this study was to determine whether an experimental method, called visual sort and rate (VSR), promoted stronger rater reliability than visual analog scale (VAS), for ratings of strain in two clinical populations: adductor laryngeal dystonia (ADLD) and vocal hyperfunction (VH).

METHOD

Connected speech samples from speakers with ADLD and VH as well as age- and sex-matched controls were selected from a database. Fifteen inexperienced listeners rated strain for two speaker sets (25 ADLD speakers and five controls; 25 VH speakers and five controls) across four rating blocks: VAS-ADLD, VSR-ADLD, VAS-VH, and VSR-VH. For the VAS task, listeners rated each speaker for strain using a vertically oriented 100-mm VAS. For the VSR task, stimuli were distributed into sets of samples with a range of severities in each set. Listeners sorted and ranked samples for strain within each set, and final ratings were captured on a vertically oriented 100-mm VAS. Intrarater reliability (Pearson's r) and interrater variability (mean of the squared differences between a listener's ratings and group mean ratings) were compared across rating methods and populations using two repeated-measures analyses of variance.

RESULTS

Intrarater reliability of strain was significantly stronger when listeners used VSR compared to VAS; listeners also showed significantly better intrarater reliability in ADLD than VH. Listeners demonstrated significantly less interrater variability (better reliability) when using VSR compared to VAS. No significant effect of population or interactions was found between listeners for measures of interrater variability.

CONCLUSIONS

VSR increases intrarater reliability for ratings of vocal strain in speakers with VH and ADLD. VSR decreases variability of auditory-perceptual judgments of strain between inexperienced listeners in these clinical populations. Future research should determine whether benefits of VSR extend to voice clinicians and/or clinical settings.

Neurectomy and Myomectomy for Treatment of Spasmodic Dysphonia

Spasmodic dysphonia (SD) is a debilitating neurological disorder affecting the muscles of voice production. Sudden involuntary movements of the vocal folds lead to phonatory breaks and to forced, strained, and strangled voice quality in adductor SD, or breathy breaks in abductor SD. There is currently no cure for spasmodic dysphonia, and the gold standard for treatment is the injection of botulinum toxin in small amounts to the intrinsic laryngeal musculature.1 However, botulinum treatment requires periodic reinjection, produces vocal instability immediately after injection, lacks uniform results among patients, and patients can develop antibodies to botulinum toxin. Long-term or permanent symptom relief would be ideal. We present four patients with adductor and one patient with abductor spasmodic dysphonia who underwent neurectomy and myomectomy for treatment. The mean age was 64 years (age range 45-83). The mean duration of adductor spasmodic dysphonia was 11.8 years. The duration of abductor spasmodic was 4 years. All patients had previously been treated with voice therapy and botulinum toxin A. The mean duration of follow up was 1.7 years. Four patients had subjective and objective improvement after surgery. One patient had subjective improvement.

An Experimental Analysis on Multicepstral Projection Representation Strategies for Dysphonia Detection

Biometrics-based authentication has become the most well-established form of user recognition in systems that demand a certain level of security. For example, the most commonplace social activities stand out, such as access to the work environment or to one's own bank account. Among all biometrics, voice receives special attention due to factors such as ease of collection, the low cost of reading devices, and the high quantity of literature and software packages available for use. However, these biometrics may have the ability to represent the individual impaired by the phenomenon known as dysphonia, which consists of a change in the sound signal due to some disease that acts on the vocal apparatus. As a consequence, for example, a user with the flu may not be properly authenticated by the recognition system. Therefore, it is important that automatic voice dysphonia detection techniques be developed. In this work, we propose a new framework based on the representation of the voice signal by the multiple projection of cepstral coefficients to promote the detection of dysphonic alterations in the voice through machine learning techniques. Most of the best-known cepstral coefficient extraction techniques in the literature are mapped and analyzed separately and together with measures related to the fundamental frequency of the voice signal, and its representation capacity is evaluated on three classifiers. Finally, the experiments on a subset of the Saarbruecken Voice Database prove the effectiveness of the proposed material in detecting the presence of dysphonia in the voice.

Effects of Cortical Stimulation on Feedback-Dependent Vocal Control in Non-Human Primates

OBJECTIVES

Hearing plays an important role in our ability to control voice, and perturbations in auditory feedback result in compensatory changes in vocal production. The auditory cortex (AC) has been proposed as an important mediator of this behavior, but causal evidence is lacking. We tested this in an animal model, hypothesizing that AC is necessary for vocal self-monitoring and feedback-dependent control, and that altering activity in AC during vocalization will interfere with vocal control.

METHODS

We implanted two marmoset monkeys (Callithrix jacchus) with bilateral AC electrode arrays. Acoustic signals were recorded from vocalizing marmosets while altering vocal feedback or electrically stimulating AC during random subsets of vocalizations. Feedback was altered by real-time frequency shifts and presented through headphones and electrical stimulation delivered to individual electrodes. We analyzed recordings to measure changes in vocal acoustics during shifted feedback and stimulation, and to determine their interaction. Results were correlated with the location and frequency tuning of stimulation sites.

RESULTS

Consistent with previous results, we found electrical stimulation alone evoked changes in vocal production. Results were stronger in the right hemisphere, but decreased with lower currents or repeated stimulation. Simultaneous stimulation and shifted feedback significantly altered vocal control for a subset of sites, decreasing feedback compensation at some and increasing it at others. Inhibited compensation was more likely at sites closer to vocal frequencies.

CONCLUSIONS

Results provide causal evidence that the AC is involved in feedback-dependent vocal control, and that it is sufficient and may also be necessary to drive changes in vocal production.

LEVEL OF EVIDENCE

N/A Laryngoscope, 133:1-10, 2023.

Laryngeal Sensory Symptoms in Spasmodic Dysphonia

OBJECTIVE

The purpose of this research was to determine whether an association between laryngeal hypersensitivity (LH) and spasmodic dysphonia (SD) exists using the LH Questionnaire (LHQ). This study also explored the prevalence of self-reported upper respiratory infection (URI) at the time of SD onset across SD phenotypes.

METHODS

Individuals with and without SD were recruited to complete an online survey measure. All respondents provided demographic information and completed the LHQ. Participants with SD were also asked to provide information about their diagnosed SD subtype and pattern of onset, including whether onset was associated with a URI. The percentage of respondents with and without SD who were classified with LH was determined based on the LHQ. Scores on the LHQ were also compared between the non-SD and the SD groups, as well as between SD phenotypes (adductor SD, abductor SD, and mixed)).

RESULTS AND CONCLUSIONS

Significant associations were found between ADSD and LH, mixed SD and LH, and URI at time of SD onset and increased severity of LH symptoms. These findings suggest that laryngeal sensory symptoms may potentially contribute to or result from motor spasms in SD and/or have implications for its pathophysiology.

Nutritional Biomarkers as Predictors of Dysphonia Severity in Patients with Ischemic Stroke

Dysphonia and malnutrition are major problems in patients who have suffered an ischemic stroke. Tools to assess dysphonia severity include the dysphonia severity index (DSI) and maximum phonation time (MPT). This study aimed to investigate whether the nutritional biomarkers transferrin, albumin, and prealbumin could be predictors of dysphonia severity. A retrospective analysis was conducted between January 2018 and October 2022. A total of 180 patients who had suffered an ischemic stroke were included. Serum transferrin, albumin, and prealbumin levels were significantly correlated with DSI and MPT levels. In a multiple regression analysis, prealbumin and transferrin were significant predictors of DSI, whereas only prealbumin was a significant predictor of MPT. Serum transferrin, albumin, and prealbumin levels in patients who have suffered an ischemic stroke may correlate with dysphonia severity as assessed using DSI and MPT. These results may provide objective evidence that nutritional biomarkers affect dysphonia severity.

How can we make better decisions about dystonic voice management?

PURPOSE OF REVIEW

The optimal diagnosis and management of dystonic voice disorders are rooted in the nuanced understanding of their phenomenology. Distinguishing between subtypes of vocal dystonia is challenging, not only because the audible and physical presentations of these dystonia's can seem similar, but also because there is a lack of scientific consensus regarding the diagnostic criteria for these conditions. To help improve the clinician's acumen we focus on outlining the classification of the top three neurological voice disorders, notably: spasmodic dysphonia, (2) spasmodic dysphonia with tremor, and essential tremor of the voice. We also provide an algorithmic approach based on current evidence-based literature to guide practitioners through the clinical diagnosis and management of each possible etiology.

RECENT FINDINGS

Much remains unknown about the subtypes of vocal dystonia, and this gap in our knowledge likely limits our ability to advance clinical management. Still, continued experience evaluating and treating these patients yields refined clinical evaluations and decision making.

SUMMARY

Improvements in our clinical decision-making can be made by acknowledging that our limited understanding of vocal dystonia may hinder what therapeutic interventions we can offer, yet our ability to accurately diagnose the dystonia is central to providing optimal patient management.

Dopamine, vocalization, and astrocytes

Dopamine, the main catecholamine neurotransmitter in the brain, is predominately produced in the basal ganglia and released to various brain regions including the frontal cortex, midbrain and brainstem. Dopamine's effects are widespread and include modulation of a number of voluntary and innate behaviors. Vigilant regulation and modulation of dopamine levels throughout the brain is imperative for proper execution of motor behaviors, in particular speech and other types of vocalizations. While dopamine's role in motor circuitry is widely accepted, its unique function in normal and abnormal speech production is not fully understood. In this perspective, we first review the role of dopaminergic circuits in vocal production. We then discuss and propose the conceivable involvement of astrocytes, the numerous star-shaped glia cells of the brain, in the dopaminergic network modulating normal and abnormal vocal productions.

Non-motor symptoms in spasmodic dysphonia: A case control-study

OBJECTIVE

Non-motor symptoms (NMS) have been identified in some focal adult-onset dystonia. In the present study we aimed to evaluate the presence of NMS in patients with spasmodic dysphonia (SD), a focal action-induced dystonia that affects intrinsic laryngeal muscle control.

METHODS

Seventeen SD patients and 17 control subjects not significantly different in age and sex were evaluated for the presence of NMS. Additionally, voice handicap index (VHI-10), reflux symptom index, neuropsychiatric symptoms and QoL were assessed by validated scales and questionnaires.

RESULTS

Patients' group significantly differed from control group in mild depressive symptoms (4.35 ± 3.9 vs. 1.47 ± 2; p=0.01), insomnia (35.3% vs. 14.7%; p=0.016), smell and taste loss (11.8% vs. 0%; p=0.033), swallowing difficulties (17.6% vs. 0%; p=0.007) and throat pain (17.6% vs. 0%; p=0.007). In the group of SD, there was no correlation between voice perception evaluated by VHI-10, number of NMS or QoL.

CONCLUSION

Patients with SD have a greater burden of depressive, smell, taste, and sleep NMS than control subjects.

[Application status and prospect of botulinum toxin A in otorhinolaryngological treatment]

Botulinum toxin A is a kind of neurotoxin produced by clostridium botulinum, and has been applied for nearly thirty years in China.The target of BTX-A is to selectively cleave the synaptosome-associated protein of 25 KD molecular mass, commonly abbreviated SNAP-25, thereby inhibiting neurotransmitter release and causing chemodenervation. The potential application of botulinum toxin A in treating the spasmodic dysphonia, hemifacial spasm, tinnitus, rhinitis has been confirmed both in clinical practice and previous studies. This paper is to review comprehensively the application status and the prospect of botulinum toxin A in otorhinolaryngological treatment.

Laryngeal vibration as a non-invasive neuromodulation therapy for spasmodic dysphonia

Spasmodic dysphonia (SD) is an incurable focal dystonia of the larynx that impairs speech and communication. Vibro-tactile stimulation (VTS) alters afferent proprioceptive input to sensorimotor cortex that controls speech. This proof-of-concept study examined the effect of laryngeal VTS on speech quality and cortical activity in 13 SD participants who vocalized the vowel /a/ while receiving VTS for 29 minutes. In response to VTS, 9 participants (69%) exhibited a reduction of voice breaks and/or a meaningful increase in smoothed cepstral peak prominence, an acoustic measure of voice/speech quality. Symptom improvements persisted for 20 minutes past VTS. Application of VTS induced a significant suppression of theta band power over the left somatosensory-motor cortex and a significant rise of gamma rhythm over right somatosensory-motor cortex. Such suppression of theta oscillations is observed in patients with cervical dystonia who apply effective sensory tricks, suggesting that VTS in SD may activate a similar neurophysiological mechanism. Results of this feasibility study indicate that laryngeal VTS modulates neuronal synchronization over sensorimotor cortex, which can induce short-term improvements in voice quality. The effects of long-term VTS and its optimal dosage for treating voice symptoms in SD are still unknown and require further systematic study.

Movement Disorders and Voice

The primary movement disorders affecting the voice are laryngeal dystonia (including spasmodic dysphonia), essential voice tremor, and Parkinson disease. Diagnosis of these conditions is clinical and based on a detailed history, voice evaluation, and physical and laryngoscopic examination. Laryngeal dystonia and essential voice tremor are hyperfunctional disorders and are treated most commonly with botulinum toxin injections. Parkinson disease is a hypofunctional disorder that may affect the voice and most commonly is treated with Lee Silverman Voice Treatment.

Intermittent theta burst stimulation over right somatosensory larynx cortex enhances vocal pitch-regulation in nonsingers

While the significance of auditory cortical regions for the development and maintenance of speech motor coordination is well established, the contribution of somatosensory brain areas to learned vocalizations such as singing is less well understood. To address these mechanisms, we applied intermittent theta burst stimulation (iTBS), a facilitatory repetitive transcranial magnetic stimulation (rTMS) protocol, over right somatosensory larynx cortex (S1) and a nonvocal dorsal S1 control area in participants without singing experience. A pitch-matching singing task was performed before and after iTBS to assess corresponding effects on vocal pitch regulation. When participants could monitor auditory feedback from their own voice during singing (Experiment I), no difference in pitch-matching performance was found between iTBS sessions. However, when auditory feedback was masked with noise (Experiment II), only larynx-S1 iTBS enhanced pitch accuracy (50-250 ms after sound onset) and pitch stability (>250 ms after sound onset until the end). Results indicate that somatosensory feedback plays a dominant role in vocal pitch regulation when acoustic feedback is masked. The acoustic changes moreover suggest that right larynx-S1 stimulation affected the preparation and involuntary regulation of vocal pitch accuracy, and that kinesthetic-proprioceptive processes play a role in the voluntary control of pitch stability in nonsingers. Together, these data provide evidence for a causal involvement of right larynx-S1 in vocal pitch regulation during singing.

The Influence of Linguistic Demand on Symptom Expression in Adductor Spasmodic Dysphonia

INTRODUCTION

Adductor Spasmodic Dysphonia (ADSD), a form of focal dystonia, has been defined as a neurogenic, task-specific disorder characterized by abrupt spasms of intrinsic laryngeal muscles that result in phonatory breaks. Voice breaks are typically isolated to propositional speech, and reported to increase in severity as speaking demand or complexity increases. Research to date has focused on variations in phonologic contexts and their influence on voice breaks. The influences of variables at lexical and syntactic levels of analysis have been less well-researched and yet may provide insight into observed variability of symptom manifestation in this rare voice disorder.

OBJECTIVES

This study investigated frequency of voice breaks over 20 standard sentences in 38 individuals with ADSD according to linguistic complexity measures including lexical density and a four-level lexical frequency and type paradigm. Two research questions about linguistic influences and ADSD symptom manifestation were posed: (1) does the frequency of voice breaks vary according to the lexical density of a string? and (2) does the frequency of voice breaks vary according to a measure of lexical frequency/type?

RESULTS

Results revealed a nonsignificant relationship between string length and voice break frequency, whereas a significant relationship was found between lexical density and voice break frequency (P = 0.029, r = 0.488). Lexical analysis results revealed a significant relationship between lexical frequency and voice breaks, with words within technical/academic classes relating to the highest rates of voice break across 38 subjects with ADSD.

CONCLUSIONS

Results from this secondary analysis provide support for the hypothesis that variation in linguistic demand may modulate symptom expression in SD. Specifically, lexical density and lexical frequency modulated the frequency of symptom expression in classic forms of SD in this purposive sample.

Atypical somatosensory-motor cortical response during vowel vocalization in spasmodic dysphonia

OBJECTIVE

Spasmodic dysphonia (SD) is a debilitating voice/speech disorder without an effective cure. To obtain a better understanding of the underlying cortical neural mechanism of the disease we analyzed electroencephalographic (EEG) signals of people with SD during voice production.

METHOD

Ten SD individuals and 10 healthy volunteers produced 50 vowel vocalization epochs of 2500 ms duration. Two EEG features were derived: (1) event-related change in spectral power during vocalization relative to rest, (2) inter-regional spectral coherence.

RESULTS

During early vocalization (500-1000 ms) the SD group showed significantly larger alpha band spectral power over the left motor cortex. During late vocalization (1000-2500 ms) SD patients showed a significantly larger gamma band coherence between left somatosensory and premotor cortical areas.

CONCLUSIONS

Two atypical patterns of cortical activity characterize the pathophysiology of spasmodic dysphonia during voice production: (1) a reduced movement-related desynchronization of motor cortical networks, (2) an excessively large synchronization between left somatosensory and premotor cortical areas.

SIGNIFICANCE

The pathophysiology of SD is characterized by an abnormally high synchronous activity within and across cortical neural networks involved in voice production that is mainly lateralized in the left hemisphere.

Phenomenology, genetics, and CNS network abnormalities in laryngeal dystonia: A 30-year experience

OBJECTIVE

Laryngeal dystonia (LD) is a functionally specific disorder of the afferent-efferent motor coordination system producing action-induced muscle contraction with a varied phenomenology. This report of long-term studies aims to review and better define the phenomenology and central nervous system abnormalities of this disorder and improve diagnosis and treatment.

METHODS

Our studies categorized over 1,400 patients diagnosed with LD over the past 33 years, including demographic and medical history records and their phenomenological presentations. Patients were grouped on clinical phenotype (adductor or abductor) and genotype (sporadic and familial) and with DNA analysis and functional magnetic resonance imaging (fMRI) to investigate brain organization differences and characterize neural markers for genotype/phenotype categorization. A number of patients with alcohol-sensitive dystonia were also studied.

RESULTS

A spectrum of LD phenomena evolved: adductor, abductor, mixed, singer's, dystonic tremor, and adductor respiratory dystonia. Patients were genetically screened for DYT (dystonia) 1, DYT4, DYT6, and DYT25 (GNAL)-and several were positive. The functional MRI studies showed distinct alterations within the sensorimotor network, and the LD patients with a family history had distinct cortical and cerebellar abnormalities. A linear discriminant analysis of fMRI findings showed a 71% accuracy in characterizing LD from normal and in characterizing adductor from abductor forms.

CONCLUSION

Continuous studies of LD patients over 30 years has led to an improved understanding of the phenomenological characteristics of this neurological disorder. Genetic and fMRI studies have better characterized the disorder and raise the possibility of making objective rather than subjective diagnoses, potentially leading to new therapeutic approaches. Laryngoscope, 128:S1-S9, 2018.