What's special about human speech? A student exercise for comparing speech production between humans and chimpanzees.

Modern humans and chimpanzees share a common ancestor on the phylogenetic tree, yet chimpanzees do not spontaneously produce speech or speech sounds. The lab exercise presented in this paper was developed for undergraduate students in a course entitled "What's Special About Human Speech?" The exercise is based on acoustic analyses of the words "cup" and "papa" as spoken by Viki, a home-raised, speech-trained chimpanzee, as well as the words spoken by a human. The analyses allow students to relate differences in articulation and vocal abilities between Viki and humans to the known anatomical differences in their vocal systems. Anatomical and articulation differences between humans and Viki include (1) potential tongue movements, (2) presence or absence of laryngeal air sacs, (3) presence or absence of vocal membranes, and (4) exhalation vs inhalation during production.

The domestication of the larynx: The neural crest connection.

Wolves howl and dogs bark, both are able to produce variants of either vocalization, but we see a distinct difference in usage between wild and domesticate. Other domesticates also show distinct changes to their vocal output: domestic cats retain meows, a distinctly subadult trait in wildcats. Such differences in acoustic output are well-known, but the causal mechanisms remain little-studied. Potential links between domestication and vocal output are intriguing for multiple reasons, and offer a unique opportunity to explore a prominent hypothesis in domestication research: the neural crest/domestication syndrome hypothesis. This hypothesis suggests that in the early stages of domestication, selection for tame individuals decreased neural crest cell (NCCs) proliferation and migration, which led to a downregulation of the sympathetic arousal system, and hence reduced fear and reactive aggression. NCCs are a transitory stem cell population crucial during embryonic development that tie to diverse tissue types and organ systems. One of these neural-crest derived systems is the larynx, the main vocal source in mammals. We argue that this connection between NCCs and the larynx provides a powerful test of the predictions of the neural crest/domestication syndrome hypothesis, discriminating its predictions from those of other current hypotheses concerning domestication.

Neuroendocrine cells initiate protective upper airway reflexes.

Airway neuroendocrine (NE) cells have been proposed to serve as specialized sensory epithelial cells that modulate respiratory behavior by communicating with nearby nerve endings. However, their functional properties and physiological roles in the healthy lung, trachea, and larynx remain largely unknown. In this work, we show that murine NE cells in these compartments have distinct biophysical properties but share sensitivity to two commonly aspirated noxious stimuli, water and acid. Moreover, we found that tracheal and laryngeal NE cells protect the airways by releasing adenosine 5'-triphosphate (ATP) to activate purinoreceptive sensory neurons that initiate swallowing and expiratory reflexes. Our work uncovers the broad molecular and biophysical diversity of NE cells across the airways and reveals mechanisms by which these specialized excitable cells serve as sentinels for activating protective responses.

Sentinels of the airways.

Epithelial cells in the larynx and trachea sense harmful cues and trigger protective reflexes.

The partial upward migration of the laryngeal motor cortex: A window to the human brain evolution.

The pioneer cortical electrical stimulation studies of the last century did not explicitly mark the location of the human laryngeal motor cortex (LMC), but only the "vocalization area" in the lower half of the lateral motor cortex. In the final years of 2010́s, neuroimaging studies did demonstrate two human cortical laryngeal representations, located at the opposing ends of the orofacial motor zone, therefore termed dorsal (LMCd) and ventral laryngeal motor cortex (LMCv). Since then, there has been a continuing debate regarding the origin, function and evolutionary significance of these areas. The "local duplication model" posits that the LMCd evolved by a duplication of an adjacent region of the motor cortex. The "duplication and migration model" assumes that the dorsal LMCd arose by a duplication of motor regions related to vocalization, such as the ancestry LMC, followed by a migration into the orofacial region of the motor cortex. This paper reviews the basic arguments of these viewpoints and suggests a new explanation, declaring that the LMCd in man is rather induced through the division of the unitary LMC in nonhuman primates, upward shift and relocation of its motor part due to the disproportional growth of the head, face, mouth, lips, and tongue motor areas in the ventral part of the human motor homunculus. This explanation may be called "expansion-division and relocation model".

Netrin-1 as A neural guidance protein in development and reinnervation of the larynx.

Neural guidance proteins participate in motor neuron migration, axonal projection, and muscle fiber innervation during development. One of the guidance proteins that participates in axonal pathfinding is Netrin-1. Despite the well-known role of Netrin-1 in embryogenesis of central nervous tissue, it is still unclear how the expression of this guidance protein contributes to primary innervation of the periphery, as well as reinnervation. This is especially true in the larynx where Netrin-1 is upregulated within the intrinsic laryngeal muscles after nerve injury and where blocking of Netrin-1 alters the pattern of reinnervation of the intrinsic laryngeal muscles. Despite this consistent finding, it is unknown how Netrin-1 expression contributes to guidance of the axons towards the larynx. Improved knowledge of Netrin-1's role in nerve regeneration and reinnervation post-injury in comparison to its role in primary innervation during embryological development, may provide insights in the search for therapeutics to treat nerve injury. This paper reviews the known functions of Netrin-1 during the formation of the central nervous system and during cranial nerve primary innervation. It also describes the role of Netrin-1 in the formation of the larynx and during recurrent laryngeal reinnervation following nerve injury in the adult.

Swallowing kinematics and submental muscles activation during a newly designed maneuver called Mouth Open Swallowing Maneuver: A comparative study.

The aim of this study was to design a new maneuver called the Mouth Open Swallowing Maneuver (MOSM), and to compare swallowing kinematics and submental muscles activation (SMA) between MOSM and two current approaches used in dysphagia rehabilitation. Fifty healthy volunteers were asked to perform three repetitions of dry swallowing (DS) (control task), the MOSM, the Mendelsohn Maneuver (MM), and the Tongue-Hold Maneuver (THM) during videofluoroscopic swallowing study accompanied with simultaneous SMA recording. Swallowing kinematics were measured by frame-by-frame analysis on hyolaryngeal movement using ImageJ. Swallowing with maximum hyolaryngeal movement and SMA during these tasks was used for comparative analysis. Vertical movement of the hyoid during the MOSM was significantly greater than those observed during the DS and the THM (p<0.001, p<0.001). Horizontal movement of the hyoid during DS and the THM was significantly greater than that observed during the MM (p = 0.001, p = 0.001). Vertical movement of the larynx during the MOSM was significantly greater than those observed during DS, MM, and THM (p<0.001). There was no significant difference between tasks in horizontal movement of the larynx (p = 0.785). SMA during the THM was significantly greater than that observed during MOSM (p = 0.002). No significant difference was found between other tasks in terms of SMA (p>0.05). The MOSM as a newly designed maneuver was significantly superior to other maneuvers in increasing vertical hyolaryngeal movement. The THM has as much effect on hyolaryngeal movement as the MM. In this study, the MOSM was shown to be effective in increasing hyolaryngeal movement. ClinicalTrials.gov Protocol Registration and Results System (PRS); the clinical trial registration number (NCT05579041).

Vocal learning-associated convergent evolution in mammalian proteins and regulatory elements.

Vocal production learning ("vocal learning") is a convergently evolved trait in vertebrates. To identify brain genomic elements associated with mammalian vocal learning, we integrated genomic, anatomical, and neurophysiological data from the Egyptian fruit bat (Rousettus aegyptiacus) with analyses of the genomes of 215 placental mammals. First, we identified a set of proteins evolving more slowly in vocal learners. Then, we discovered a vocal motor cortical region in the Egyptian fruit bat, an emergent vocal learner, and leveraged that knowledge to identify active cis-regulatory elements in the motor cortex of vocal learners. Machine learning methods applied to motor cortex open chromatin revealed 50 enhancers robustly associated with vocal learning whose activity tended to be lower in vocal learners. Our research implicates convergent losses of motor cortex regulatory elements in mammalian vocal learning evolution.

Striking a (vocal) chord: musical instruments as mnemonic devices when teaching the functional anatomy of the larynx.

Mnemonic devices are memory aids that make it easier to recall information and are widely used by students studying anatomy and physiology. Simple musical instruments and toys can serve as mnemonic devices for students learning the functional anatomy of the larynx: balloons can help learners understand and recall how sound is produced; tuning pegs can help learners understand how tension affects vocal pitch; fingers on a fretboard can help learners understand how pitch is further modulated; and a common coach's whistle can demonstrate how vocal volume is controlled. Using instruments and toys engages adult learners and helps them connect complex laryngeal anatomy with previous experiences.NEW & NOTEWORTHY Musical instruments and toys can be used as mnemonic devices to help students recall and understand the functional anatomy of voice production. The mnemonics can be implemented in a variety of classrooms and are flexible and engaging.

An open-source toolbox for measuring vocal tract shape from real-time magnetic resonance images.

Real-time magnetic resonance imaging (rtMRI) is a technique that provides high-contrast videographic data of human anatomy in motion. Applied to the vocal tract, it is a powerful method for capturing the dynamics of speech and other vocal behaviours by imaging structures internal to the mouth and throat. These images provide a means of studying the physiological basis for speech, singing, expressions of emotion, and swallowing that are otherwise not accessible for external observation. However, taking quantitative measurements from these images is notoriously difficult. We introduce a signal processing pipeline that produces outlines of the vocal tract from the lips to the larynx as a quantification of the dynamic morphology of the vocal tract. Our approach performs simple tissue classification, but constrained to a researcher-specified region of interest. This combination facilitates feature extraction while retaining the domain-specific expertise of a human analyst. We demonstrate that this pipeline generalises well across datasets covering behaviours such as speech, vocal size exaggeration, laughter, and whistling, as well as producing reliable outcomes across analysts, particularly among users with domain-specific expertise. With this article, we make this pipeline available for immediate use by the research community, and further suggest that it may contribute to the continued development of fully automated methods based on deep learning algorithms.

The Application of Superior Laryngeal Nerve Block for Non-Cough Laryngeal Hypersensitivity.

OBJECTIVE(S): To investigate the effect of superior laryngeal nerve (SLN) block in patients with non-cough complaints relating to laryngeal who have failed conventional medical therapy. METHODS: Retrospective chart review of 46 patients who underwent SLN block for non-cough indications between July 2019 and March 2022 was performed. Demographics, comorbidities, and patient-reported outcomes were collected. The primary diagnoses for this group included: odynophagia, throat pain, cervicalgia, muscle tension dysphonia, globus sensation, hyoid bone syndrome, and Eagle syndrome. RESULTS: The cohort underwent an average of 1.24 bilateral injections (range 0-7) and 0.87 unilateral injections (range 0-4). About 35 of 46 patients reported an average of 51.0% improvement in their symptoms, with the treatment effect lasting 7.60 weeks on average. On subgroup analysis, the patients with spasmodic dysphonia, odynophagia, and hyoid bone syndrome had the best percent improvement on average (75%-77.5%). Patients with globus sensation had the lowest percent improvement on average in response to this therapy, reporting only about 25%. Five patients experienced a mild adverse reaction immediately following injection which resolved spontaneously. CONCLUSION: The use of in-office SLN block for non-cough disorders involving the larynx requires further study with larger sample sizes to better delineate the efficacy of these applications. LEVEL OF EVIDENCE: 4 Laryngoscope, 134:1765-1768, 2024.

Videofluoroscopic analysis of the laryngeal movement of older adults in swallowing.

Even without diseases that cause dysphagia, physiological swallowing function declines with age, increasing the risk of aspiration. This study analyzed age-related changes in laryngeal movement in older adults. The study population consisted of 10 volunteers in their 80s and six in their 20s. A videofluoroscopic study of 3 and 10 mL barium swallows was performed laterally using a digital fluorographic. The recorded images were retrieved to a personal computer and analyzed frame-by-frame using video analysis software. The movement of the larynx during swallowing, barium's pharyngeal transit time (PTT), and laryngeal elevation delay time (LEDT) were analyzed. Results were compared between the 20s and 80s age groups using statistical analyses. The PTT was shorter in the 20s than in the 80s age group. The PTT was significantly longer in the 80s group than in the 20s for both 3 and 10 mL barium swallows. LEDT in the 80s was statistically significantly longer than that in the 20s for the 10 ml barium. No statistically significant differences were found; however, there was a tendency for the 80s group to have more types of laryngeal movement velocity peaks. In this study, LEDT was prolonged in the 80s with 10 ml barium swallowing than in the 20s. Two peak patterns of laryngeal elevation during swallowing were observed. The velocity peaks showed a two-peak pattern when the patients were in their 80s and when the barium volume was tested at 10 mL. Our results suggest that aging's effect on swallowing relates to laryngeal elevation.

A Tutorial on Skeletal Muscle Metabolism and the Role of Blood Lactate: Implications for Speech Production.

PURPOSE: The purpose of this tutorial is threefold: (a) present relevant exercise science literature on skeletal muscle metabolism and synthesize the limited available research on metabolism of the adult human speech musculature in an effort to elucidate the role of metabolism in speech production; (b) introduce a well-studied metabolic serum biomarker in exercise science, lactate, and the potential usefulness of investigating this metabolite, through a well-established exercise science methodology, to better understand metabolism of the musculature involved in voice production; and (c) discuss exercise physiology considerations for future voice science research that seeks to investigate blood lactate and metabolism in voice physiology in an ecologically valid manner. METHOD: This tutorial begins with relevant exercise science literature on the basic cellular processes of muscle contraction that require energy and the metabolic mechanisms that regenerate the energy required for task execution. The tutorial next synthesizes the available research investigating metabolism of the adult human speech musculature. This is followed by the authors proposing a hypothesis of speech metabolism based on the voice science literature and the application of well-studied exercise science principles of muscle physiology. The tutorial concludes with a discussion and the potential usefulness of lactate in investigations to better understand the metabolism of the musculature involved in vocal demand tasks. CONCLUSION: The role of metabolism during speech (respiratory, laryngeal, and articulatory) is an understudied yet critical aspect of speech physiology that warrants further study to better understand the metabolic systems that are used to meet vocal demands.

Vocal communication: The enigmatic production of low-frequency purrs in cats.

Cat purring, the unusual, pulsed vibration that epitomizes comfort, enjoys a special status in the world of vocal communication research. Indeed, it has long been flagged as a rare exception to the dominant theory of voice production in mammals. A new study presents histological and biomechanical evidence that purring can occur passively, without needing muscle vibration in the larynx controlled by an independent neural oscillator.

A brainstem circuit for phonation and volume control in mice.

Mammalian vocalizations are critical for communication and are produced through the process of phonation, in which expiratory muscles force air through the tensed vocal folds of the larynx, which vibrate to produce sound. Despite the importance of phonation, the motor circuits in the brain that control it remain poorly understood. In this study, we identified a subpopulation of ~160 neuropeptide precursor Nts (neurotensin)-expressing neurons in the mouse brainstem nucleus retroambiguus (RAm) that are robustly activated during both neonatal isolation cries and adult social vocalizations. The activity of these neurons is necessary and sufficient for vocalization and bidirectionally controls sound volume. RAm Nts neurons project to all brainstem and spinal cord motor centers involved in phonation and activate laryngeal and expiratory muscles essential for phonation and volume control. Thus, RAm Nts neurons form the core of a brain circuit for making sound and controlling its volume, which are two foundations of vocal communication.

The influence of source-filter interaction on the voice source in a three-dimensional computational model of voice production.

The goal of this computational study is to quantify global effects of vocal tract constriction at various locations (false vocal folds, aryepiglottic folds, pharynx, oral cavity, and lips) on the voice source across a large range of vocal fold conditions. The results showed that while inclusion of a uniform vocal tract had notable effects on the voice source, further constricting the vocal tract only had small effects except for conditions of extreme constriction, at which constrictions at any location along the vocal tract decreased the mean and peak-to-peak amplitude of the glottal flow waveform. Although narrowing in the epilarynx increased the normalized maximum flow declination rate, vocal tract constriction in general slightly reduced the source strength and high-frequency harmonic production at the glottis, except for a limited set of vocal fold conditions (e.g., soft, long vocal folds subject to relatively high pressure). This suggests that simultaneous laryngeal and vocal tract adjustments are required to maximize source-filter interaction. While vocal tract adjustments are often assumed to improve voice production, our results indicate that such improvements are mainly due to changes in vocal tract acoustic response rather than improved voice production at the glottis.

Domestic cat larynges can produce purring frequencies without neural input.

Most mammals produce vocal sounds according to the myoelastic-aerodynamic (MEAD) principle, through self-sustaining oscillation of laryngeal tissues.1,2 In contrast, cats have long been believed to produce their low-frequency purr vocalizations through a radically different mechanism involving active muscle contractions (AMC), where neurally driven electromyographic burst patterns (typically at 20-30 Hz) cause the intrinsic laryngeal muscles to actively modulate the respiratory airflow. Direct empirical evidence for this AMC mechanism is sparse.3 Here, the fundamental frequency (fo) ranges of eight domestic cats (Felis silvestris catus) were investigated in an excised larynx setup, to test the prediction of the AMC hypothesis that vibration should be impossible without neuromuscular activity, and thus unattainable in excised larynx setups, which are based on MEAD principles. Surprisingly, all eight excised larynges produced self-sustained oscillations at typical cat purring rates. Histological analysis of cat larynges revealed the presence of connective tissue masses, up to 4 mm in diameter, embedded in the vocal fold.4 This vocal fold specialization appears to allow the unusually low fo values observed in purring. While our data do not fully reject the AMC hypothesis for purring, they show that cat larynges can easily produce sounds in the purr regime with fundamental frequencies of 25 to 30 Hz without neural input or muscular contraction. This strongly suggests that the physical and physiological basis of cat purring involves the same MEAD-based mechanisms as other cat vocalizations (e.g., meows) and most other vertebrate vocalizations but is potentially augmented by AMC.

Defining Normal Sequential Swallowing Biomechanics.

Little is known about the physiology of a common fluid ingestion pattern-sequential swallowing. This study investigated sequential swallowing biomechanics in healthy adults. Archival normative videofluoroscopic swallow studies were analyzed for hyolaryngeal complex (HLC) patterning and biomechanical measures from the first 2 swallows of a 90-mL thin liquid sequential swallow task. The effects of age, sex, HLC type, and swallow order were explored. Eighty-eight participants were included in the primary analyses as they performed sequential swallows. HLC Type I (airway opens, epiglottis approaches baseline) and Type II (airway remains closed, epiglottis remains inverted) most commonly occurred (47% each), followed by Type III (mixed, 6%). Age was significantly associated with Type II and longer hypopharyngeal transit, total pharyngeal transit (TPT), swallow reaction time (SRT), and duration to maximum hyoid elevation. Males demonstrated significantly greater maximum hyoid displacement (Hmax) and longer duration of maximum hyoid displacement. Significantly larger maximum hyoid-to-larynx approximation was linked to the first swallow, while the subsequent swallow had significantly longer oropharyngeal transit, TPT, and SRT. Secondary analyses included an additional 91 participants who performed a series of discrete swallows for the same swallow task. Type II had significantly greater Hmax than Type I and series of discrete swallows. Sequential swallowing biomechanics differ from discrete swallows, and normal variance exists among healthy adults. In vulnerable populations, sequential swallowing may challenge swallow coordination and airway protection. Normative data allow comparison to dysphagic populations. Systematic efforts are needed to further standardize a definition for sequential swallowing.