Laryngeal motor cortex and control of speech in humans

The central role of the individual in the history of brains

Every species' brain, body and behavior is shaped by the contingencies of their evolutionary history; these exert pressures that change their developmental trajectories. There is, however, another set of contingencies that shape us and other animals: those that occur during a lifetime. In this perspective piece, we show how these two histories are intertwined by focusing on the individual. We suggest that organisms--their brains and behaviors--are not solely the developmental products of genes and neural circuitry but individual centers of action unfolding in time. To unpack this idea, we first emphasize the importance of variation and the central role of the individual in biology. We then go over "errors in time" that we often make when comparing development across species. Next, we reveal how an individual's development is a process rather than a product by presenting a set of case studies. These show developmental trajectories as emerging in the contexts of the "the actual now" and "the presence of the past". Our consideration reveals that individuals are slippery-they are never static; they are a set of on-going, creative activities. In light of this, it seems that taking individual development seriously is essential if we aspire to make meaningful comparisons of neural circuits and behavior within and across species.

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".

The speech neuroprosthesis

Loss of speech after paralysis is devastating, but circumventing motor-pathway injury by directly decoding speech from intact cortical activity has the potential to restore natural communication and self-expression. Recent discoveries have defined how key features of speech production are facilitated by the coordinated activity of vocal-tract articulatory and motor-planning cortical representations. In this Review, we highlight such progress and how it has led to successful speech decoding, first in individuals implanted with intracranial electrodes for clinical epilepsy monitoring and subsequently in individuals with paralysis as part of early feasibility clinical trials to restore speech. We discuss high-spatiotemporal-resolution neural interfaces and the adaptation of state-of-the-art speech computational algorithms that have driven rapid and substantial progress in decoding neural activity into text, audible speech, and facial movements. Although restoring natural speech is a long-term goal, speech neuroprostheses already have performance levels that surpass communication rates offered by current assistive-communication technology. Given this accelerated rate of progress in the field, we propose key evaluation metrics for speed and accuracy, among others, to help standardize across studies. We finish by highlighting several directions to more fully explore the multidimensional feature space of speech and language, which will continue to accelerate progress towards a clinically viable speech neuroprosthesis.

Genetic association analysis of human median voice pitch identifies a common locus for tonal and non-tonal languages

The genetic influence on human vocal pitch in tonal and non-tonal languages remains largely unknown. In tonal languages, such as Mandarin Chinese, pitch changes differentiate word meanings, whereas in non-tonal languages, such as Icelandic, pitch is used to convey intonation. We addressed this question by searching for genetic associations with interindividual variation in median pitch in a Chinese major depression case-control cohort and compared our results with a genome-wide association study from Iceland. The same genetic variant, rs11046212-T in an intron of the ABCC9 gene, was one of the most strongly associated loci with median pitch in both samples. Our meta-analysis revealed four genome-wide significant hits, including two novel associations. The discovery of genetic variants influencing vocal pitch across both tonal and non-tonal languages suggests the possibility of a common genetic contribution to the human vocal system shared in two distinct populations with languages that differ in tonality (Icelandic and Mandarin).

Neuroanatomical frameworks for volitional control of breathing and orofacial behaviors

Breathing is the only vital function that can be volitionally controlled. However, a detailed understanding how volitional (cortical) motor commands can transform vital breathing activity into adaptive breathing patterns that accommodate orofacial behaviors such as swallowing, vocalization or sniffing remains to be developed. Recent neuroanatomical tract tracing studies have identified patterns and origins of descending forebrain projections that target brain nuclei involved in laryngeal adductor function which is critically involved in orofacial behavior. These nuclei include the midbrain periaqueductal gray and nuclei of the respiratory rhythm and pattern generating network in the brainstem, specifically including the pontine Kölliker-Fuse nucleus and the pre-Bötzinger complex in the medulla oblongata. This review discusses the functional implications of the forebrain-brainstem anatomical connectivity that could underlie the volitional control and coordination of orofacial behaviors with breathing.

Predictive modeling of neuroticism in depressed and non-depressed cohorts using voice features

BACKGROUND

Neuroticism's impact on psychopathological and physical health issues has significant public health implications. Multiple studies confirm its predictive effect on suicide risk among depressed patients. However, previous research lacks a standardized criterion for assessing neuroticism through speech, often relying on simple features (such as pitch, loudness and MFCCs). This study aims to improve upon this by extracting features using advanced pre-trained speaker embedding models (i-vector and x-vector extractors). Additionally, unlike prior studies utilizing general population data, we explore neuroticism prediction in depressed and non-depressed subgroups.

METHODS

We collected edited discourse data from clinical interviews of 3580 depressed individuals and 4016 healthy individuals from the CONVERGE study. Instead of solely extracting Low-Level Acoustic Descriptors, we incorporated i-vector and x-vector features. We compared the performance of three different features in predicting neuroticism and explored their combination to enhance model accuracy.

RESULTS

The SVR model, combining three speech features with downscaled features to 300, exhibited the highest performance in predicting neuroticism scores. It achieved a coefficient of determination (R-squared) of 0.3 or higher and a correlation of 0.56 between predicted and actual values. The predictive classification accuracy of speech features for neuroticism in specific populations (healthy and depressed) exceeded 60 %.

LIMITATIONS

This study included only women.

CONCLUSION

Combining diverse speech features enhances the predictive capacity of models using speech features to assess neuroticism, particularly in specific populations. This study lays the foundation for future exploration of speech features in neuroticism prediction.

The uniqueness of the human brain: a review

The purpose of this review is to highlight the most important aspects of the anatomical and functional uniqueness of the human brain. For this, a comparison is made between our brains and those of our closest ancestors (chimpanzees and bonobos) and human ancestors. During human evolution, several changes occurred in the brain, such as an absolute increase in brain size and number of cortical neurons, in addition to a greater degree of functional lateralization and anatomical asymmetry. Also, the cortical cytoarchitecture became more diversified and there was an increase in the number of intracortical networks and networks extending from the cerebral cortex to subcortical structures, with more neural networks being invested in multisensory and sensory-motor-affective-cognitive integration. These changes permitted more complex, flexible and versatile cognitive abilities and social behavior, such as shared intentionality and symbolic articulated language, which, in turn, made possible the formation of larger social groups and cumulative cultural evolution that are characteristic of our species.

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.

Speech-Swallow Dissociation of Velopharyngeal Incompetence with Pseudobulbar Palsy: Evaluation by High-Resolution Manometry

Patients with pseudobulbar palsy often present with velopharyngeal incompetence. Velopharyngeal incompetence is usually observed during expiratory activities such as speech and/or blowing during laryngoscopy. These patients typically exhibit good velopharyngeal closure during swallowing, which is dissociated from expiratory activities. We named this phenomenon "speech-swallow dissociation" (SSD). SSD on endoscopic findings can help in diagnosing the underlying disease causing dysphagia. This endoscopic finding is qualitative, and the quantitative characteristics of SSD are still unclear. Accordingly, the current study aimed to quantitatively evaluate SSD in patients with pseudobulbar palsy. We evaluated velopharyngeal pressure during swallowing and expiratory activity in 10 healthy subjects and 10 patients with pseudobulbar palsy using high-resolution manometry, and compared the results between the two groups. No significant differences in maximal velopharyngeal contraction pressure (V-Pmax) were observed during dry swallowing between the pseudobulbar palsy group and healthy subjects (190.5 mmHg vs. 173.6 mmHg; P = 0.583). V-Pmax during speech was significantly decreased in the pseudobulbar palsy group (85.4 mmHg vs. 34.5 mmHg; P < 0.001). The degree of dissociation of speech to swallowing in V-Pmax, when compared across groups, exhibited a larger difference in the pseudobulbar palsy group, at 52% versus 80% (P = 0.001). Velopharyngeal pressure during blowing was similar to that during speech. Velopharyngeal closure in patients with pseudobulbar palsy exhibited weaker pressure during speech and blowing compared with swallowing, quantitatively confirming the presence of SSD. Pseudobulbar palsy often presents with SSD, and this finding may be helpful in differentiating the etiology of dysphagia.

On the interplay between speech perception and production: insights from research and theories

The study of spoken communication has long been entrenched in a debate surrounding the interdependence of speech production and perception. This mini review summarizes findings from prior studies to elucidate the reciprocal relationships between speech production and perception. We also discuss key theoretical perspectives relevant to speech perception-production loop, including hyper-articulation and hypo-articulation (H&H) theory, speech motor theory, direct realism theory, articulatory phonology, the Directions into Velocities of Articulators (DIVA) and Gradient Order DIVA (GODIVA) models, and predictive coding. Building on prior findings, we propose a revised auditory-motor integration model of speech and provide insights for future research in speech perception and production, focusing on the effects of impaired peripheral auditory systems.

Association Between Acoustic Features and Brain Volumes: the Framingham Heart Study

Introduction

Although brain magnetic resonance imaging (MRI) is a valuable tool for investigating structural changes in the brain associated with neurodegeneration, the development of non-invasive and cost-effective alternative methods for detecting early cognitive impairment is crucial. The human voice has been increasingly used as an indicator for effectively detecting cognitive disorders, but it remains unclear whether acoustic features are associated with structural neuroimaging.

Methods

This study aims to investigate the association between acoustic features and brain volume and compare the predictive power of each for mild cognitive impairment (MCI) in a large community-based population. The study included participants from the Framingham Heart Study (FHS) who had at least one voice recording and an MRI scan. Sixty-five acoustic features were extracted with the OpenSMILE software (v2.1.3) from each voice recording. Nine MRI measures were derived according to the FHS MRI protocol. We examined the associations between acoustic features and MRI measures using linear regression models adjusted for age, sex, and education. Acoustic composite scores were generated by combining acoustic features significantly associated with MRI measures. The MCI prediction ability of acoustic composite scores and MRI measures were compared by building random forest models and calculating the mean area under the receiver operating characteristic curve (AUC) of 10-fold cross-validation.

Results

The study included 4,293 participants (age 57 ± 13 years, 53.9% women). During 9.3±3.7 years follow-up, 106 participants were diagnosed with MCI. Seven MRI measures were significantly associated with more than 20 acoustic features after adjusting for multiple testing. The acoustic composite scores can improve the AUC for MCI prediction to 0.794, compared to 0.759 achieved by MRI measures.

Discussion

We found multiple acoustic features were associated with MRI measures, suggesting the potential for using acoustic features as easily accessible digital biomarkers for the early diagnosis of MCI.

Cerebellar mutism is linked to midbrain volatility and desynchronization from speech cortices

Cerebellar mutism syndrome is a disorder of speech, movement and affect that can occur after tumour removal from the posterior fossa. Projections from the fastigial nuclei to the periaqueductal grey area were recently implicated in its pathogenesis, but the functional consequences of damaging these projections remain poorly understood. Here, we examine functional MRI data from patients treated for medulloblastoma to identify functional changes in key brain areas that comprise the motor system for speech, which occur along the timeline of acute speech impairment in cerebellar mutism syndrome. One hundred and twenty-four participants, all with medulloblastoma, contributed to the study: 45 with cerebellar mutism syndrome, 11 patients with severe postoperative deficits other than mutism, and 68 without either (asymptomatic). We first performed a data-driven parcellation to spatially define functional nodes relevant to the cohort that align with brain regions critical for the motor control of speech. We then estimated functional connectivity between these nodes during the initial postoperative imaging sessions to identify functional deficits associated with the acute phase of the disorder. We further analysed how functional connectivity changed over time within a subset of participants that had suitable imaging acquired over the course of recovery. Signal dispersion was also measured in the periaqueductal grey area and red nuclei to estimate activity in midbrain regions considered key targets of the cerebellum with suspected involvement in cerebellar mutism pathogenesis. We found evidence of periaqueductal grey dysfunction in the acute phase of the disorder, with abnormal volatility and desynchronization with neocortical language nodes. Functional connectivity with periaqueductal grey was restored in imaging sessions that occurred after speech recovery and was further shown to be increased with left dorsolateral prefrontal cortex. The amygdalae were also broadly hyperconnected with neocortical nodes in the acute phase. Stable connectivity differences between groups were broadly present throughout the cerebrum, and one of the most substantial differences-between Broca's area and the supplementary motor area-was found to be inversely related to cerebellar outflow pathway damage in the mutism group. These results reveal systemic changes in the speech motor system of patients with mutism, centred on limbic areas tasked with the control of phonation. These findings provide further support for the hypothesis that periaqueductal grey dysfunction (following cerebellar surgical injury) contributes to the transient postoperative non-verbal episode commonly observed in cerebellar mutism syndrome but highlights a potential role of intact cerebellocortical projections in chronic features of the disorder.

Relative importance of speech and voice features in the classification of schizophrenia and depression

Speech is a promising biomarker for schizophrenia spectrum disorder (SSD) and major depressive disorder (MDD). This proof of principle study investigates previously studied speech acoustics in combination with a novel application of voice pathology features as objective and reproducible classifiers for depression, schizophrenia, and healthy controls (HC). Speech and voice features for classification were calculated from recordings of picture descriptions from 240 speech samples (20 participants with SSD, 20 with MDD, and 20 HC each with 4 samples). Binary classification support vector machine (SVM) models classified the disorder groups and HC. For each feature, the permutation feature importance was calculated, and the top 25% most important features were used to compare differences between the disorder groups and HC including correlations between the important features and symptom severity scores. Multiple kernels for SVM were tested and the pairwise models with the best performing kernel (3-degree polynomial) were highly accurate for each classification: 0.947 for HC vs. SSD, 0.920 for HC vs. MDD, and 0.932 for SSD vs. MDD. The relatively most important features were measures of articulation coordination, number of pauses per minute, and speech variability. There were moderate correlations between important features and positive symptoms for SSD. The important features suggest that speech characteristics relating to psychomotor slowing, alogia, and flat affect differ between HC, SSD, and MDD.

The importance of the dorsal branch of the arcuate fasciculus in phonological working memory

Phonological working memory (PWM) is important for language learning and processing. The most studied language brain regions are the classical Broca's area on the inferior frontal gyrus and Wernicke's area on the posterior temporal region and their anatomical connection via the classic arcuate fasciculus (AF) referred to here as the ventral AF (AFv). However, areas on the middle frontal gyrus (MFG) are essential for PWM processes. There is also a dorsal branch of the AF (AFd) that specifically links the posterior temporal region with the MFG. Furthermore, there is the temporo-frontal extreme capsule fasciculus (TFexcF) that courses ventrally and links intermediate temporal areas with the lateral prefrontal cortex. The AFv, AFd and TFexcF were dissected virtually in the same participants who performed a PWM task in a functional magnetic resonance imaging study. The results showed that good performance on the PWM task was exclusively related to the properties of the left AFd, which specifically links area 8A (known to be involved in attentional aspects of executive control) with the posterior temporal region. The TFexcF, consistent with its known anatomical connection, was related to brain activation in area 9/46v of the MFG that is critical for monitoring the information in memory.

Singing training predicts increased insula connectivity with speech and respiratory sensorimotor areas at rest

The insula contributes to the detection of salient events during goal-directed behavior and participates in the coordination of motor, multisensory, and cognitive systems. Recent task-fMRI studies with trained singers suggest that singing experience can enhance the access to these resources. However, the long-term effects of vocal training on insula-based networks are still unknown. In this study, we employed resting-state fMRI to assess experience-dependent differences in insula co-activation patterns between conservatory-trained singers and non-singers. Results indicate enhanced bilateral anterior insula connectivity in singers relative to non-singers with constituents of the speech sensorimotor network. Specifically, with the cerebellum (lobule V-VI) and the superior parietal lobes. The reversed comparison showed no effects. The amount of accumulated singing training predicted enhanced bilateral insula co-activation with primary sensorimotor areas representing the diaphragm and the larynx/phonation area-crucial regions for cortico-motor control of complex vocalizations-as well as the bilateral thalamus and the left putamen. Together, these findings highlight the neuroplastic effect of expert singing training on insula-based networks, as evidenced by the association between enhanced insula co-activation profiles in singers and the brain's speech motor system components.

Large Language Models and the Reverse Turing Test

Large language models (LLMs) have been transformative. They are pretrained foundational models that are self-supervised and can be adapted with fine-tuning to a wide range of natural language tasks, each of which previously would have required a separate network model. This is one step closer to the extraordinary versatility of human language. GPT-3 and, more recently, LaMDA, both of them LLMs, can carry on dialogs with humans on many topics after minimal priming with a few examples. However, there has been a wide range of reactions and debate on whether these LLMs understand what they are saying or exhibit signs of intelligence. This high variance is exhibited in three interviews with LLMs reaching wildly different conclusions. A new possibility was uncovered that could explain this divergence. What appears to be intelligence in LLMs may in fact be a mirror that reflects the intelligence of the interviewer, a remarkable twist that could be considered a reverse Turing test. If so, then by studying interviews, we may be learning more about the intelligence and beliefs of the interviewer than the intelligence of the LLMs. As LLMs become more capable, they may transform the way we interact with machines and how they interact with each other. Increasingly, LLMs are being coupled with sensorimotor devices. LLMs can talk the talk, but can they walk the walk? A road map for achieving artificial general autonomy is outlined with seven major improvements inspired by brain systems and how LLMs could in turn be used to uncover new insights into brain function.

Articulatory effects on perceptions of men's status and attractiveness

Research on heterosexual mating has demonstrated that acoustic parameters (e.g., pitch) of men's voices influence their attractiveness to women and appearance of status and formidability to other men. However, little is known about how men's tendency to clearly articulate their speech influences these important social perceptions. In the current study, we used a repeated-measures design to investigate how men's articulatory clarity or conformity influenced women's (N = 45) evaluations of men's attractiveness for both short- and long-term relationships, and men's (N = 46) evaluations of physical formidability and prestige. Results largely supported our hypotheses: men who enunciated phonemes more distinctly were more attractive to women for long-term relationships than short-term relationships and were perceived by other men to have higher prestige than physical dominance. These findings suggest that aspects of articulatory behavior that influence perceptions of prestige and long-term mating attractiveness may indicate an early social history characterized by high socioeconomic status, likely owing to crystallization of articulatory patterns during the critical period of language development. These articulatory patterns may also be honest signals of condition or disposition owing to the nature of complex, multicomponent traits, which deserve further empirical attention.

Investigating the Impact of Voice Impairment on Quality of Life in Stroke Patients: The Voice Handicap Index (VHI) Questionnaire Study

The Voice Handicap Index (VHI) is a patient-centered evaluation tool specifically designed for assessing voice-related quality of life. Although the VHI has been extensively used in patients with voice disorders, its applicability in stroke patients has not been fully established. This prospective cross-sectional study aimed to investigate the feasibility of using the VHI questionnaire in identifying stroke patients with voice problems. The study included a cohort of acute to subacute first-ever stroke patients (n = 48), with or without voice problems, as well as other non-stroke patients (n = 31) who agreed to complete the VHI questionnaire. Stroke patients with self-reported voice problems demonstrated significantly higher VHI scores and poorer life quality scores compared to the control groups. These patients also had lower Mini-Mental State Examination (MMSE), Modified Barthel Index (MBI), and Euro-QoL-5D-5L (EQ-5D-5L) scores. Spearman correlation analysis revealed an inverse association between VHI scores and EQ-5D-5L (rho = -0.77, p < 0.001), Korean Mann Assessment of Swallowing Ability (rho = -0.51, p < 0.001), and other functional parameters, including the National Institutes of Health Stroke Scale, MMSE, and MBI scores. Multiple regression analysis indicated that the VHI score was the biggest contributing factor to EQ scores. This is the first study to demonstrate that stroke patients with voice problems may experience reduced quality of life, even after controlling for other confounding factors such as dysphagia or neurological deficits. Future studies are needed whether addressing these issues by implementing the VHI may facilitate the improvement of patients' quality of life.

Analogies of human speech and bird song: From vocal learning behavior to its neural basis

Vocal learning is a complex acquired social behavior that has been found only in very few animals. The process of animal vocal learning requires the participation of sensorimotor function. By accepting external auditory input and cooperating with repeated vocal imitation practice, a stable pattern of vocal information output is eventually formed. In parallel evolutionary branches, humans and songbirds share striking similarities in vocal learning behavior. For example, their vocal learning processes involve auditory feedback, complex syntactic structures, and sensitive periods. At the same time, they have evolved the hierarchical structure of special forebrain regions related to vocal motor control and vocal learning, which are organized and closely associated to the auditory cortex. By comparing the location, function, genome, and transcriptome of vocal learning-related brain regions, it was confirmed that songbird singing and human language-related neural control pathways have certain analogy. These common characteristics make songbirds an ideal animal model for studying the neural mechanisms of vocal learning behavior. The neural process of human language learning may be explained through similar neural mechanisms, and it can provide important insights for the treatment of language disorders.

Preparing to sing: respiratory patterns underlying motor readiness for song

Evidence for motor preparation and planning comes from neural activity preceding neural commands to activate the effectors; such preparatory activity is observed in pallial areas controlling learned motor behaviors. Vocal learning in songbirds is an example of a learned, sequential motor behavior that is a respiratory motor act and where there is evidence for neuromuscular planning. Respiration is the foundation of vocalization, elucidating the neural control of song motor planning requires studying respiratory antecedents of song initiation. Despite the importance of respiration in song production, few studies have investigated respiratory antecedents of impending vocalizations. Therefore, we investigated respiratory patterns in male zebra finches (Taeniopygia guttata) and Bengalese finches (Lonchura striata domestica) prior to, during, and following song bouts. In both species, compared with quiet respiration, song respiratory patterns were generated with higher amplitude, faster tempo, and ∼70% of the respiratory cycle is in the expiratory phase. In female-directed and isolation song, both species show a change in the respiratory tempo and the proportion of time spent inhaling prior to song. Following song, only zebra finches show systematic changes in respiratory patterns; they spend a greater proportion of the respiratory cycle in the expiratory phase for 1 s after song, which is likely due to hyperventilation during song. Accelerated respiratory rhythms before song may reflect the motor preparation for the upcoming song production; species differences in preparatory motor activity could be related to the degree to which motor planning is required; finally, song termination may be dictated by respiratory demands.NEW & NOTEWORTHY Motor planning for vocal production in birdsong manifests as an adaptation of respiratory characteristics prior to song. The songbird's respiratory system anticipates the upcoming song production by accelerating the respiratory tempo and increasing the proportion of time spent inhaling.

A causal link between left supplementary motor area and auditory-motor control of vocal production: Evidence by continuous theta burst stimulation

The supplementary motor area (SMA) has been implicated in the feedforward control of speech production. Whether this region is involved in speech motor control through auditory feedback, however, remains uncertain. The present event-related potential (ERP) study examined the role of the left SMA in vocal pitch regulation in a causal manner by combining auditory feedback manipulations and neuronavigated continuous theta bust stimulation (c-TBS). After receiving c-TBS over the left SMA or the control site (vertex), twenty young adults vocalized the vowel sound /u/ while hearing their voice unexpectedly pitch-shifted -50 or -200 cents. Compared to the control stimulation, c-TBS over the left SMA led to decreased vocal compensations for pitch perturbations of -50 and -200 cents. A significant decrease of N1 and P2 responses to -200 cents perturbations was also found when comparing active and control stimulation. Major neural generators of decreased P2 responses included the right-lateralized superior and middle temporal gyrus and angular gyrus. Notably, a significant correlation was found between active-control differences in the vocal compensation and P2 responses for the -200 cents perturbations. These findings provide neurobehavioral evidence for a causal link between the left SMA and auditory-motor integration for vocal pitch regulation, suggesting that the left SMA receives auditory feedback information and mediates vocal compensations for feedback errors in a bottom-up manner.

Convergent and divergent neural circuit architectures that support acoustic communication

Vocal communication is used across extant vertebrates, is evolutionarily ancient, and been maintained, in many lineages. Here I review the neural circuit architectures that support intraspecific acoustic signaling in representative anuran, mammalian and avian species as well as two invertebrates, fruit flies and Hawaiian crickets. I focus on hindbrain motor control motifs and their ties to respiratory circuits, expression of receptors for gonadal steroids in motor, sensory, and limbic neurons as well as divergent modalities that evoke vocal responses. Hindbrain and limbic participants in acoustic communication are highly conserved, while forebrain participants have diverged between anurans and mammals, as well as songbirds and rodents. I discuss the roles of natural and sexual selection in driving speciation, as well as exaptation of circuit elements with ancestral roles in respiration, for producing sounds and driving rhythmic vocal features. Recent technical advances in whole brain fMRI across species will enable real time imaging of acoustic signaling partners, tying auditory perception to vocal production.

When laughter arrests speech: fMRI-based evidence

Who has not experienced that sensation of losing the power of speech owing to an involuntary bout of laughter? An investigation of this phenomenon affords an insight into the neuronal processes that underlie laughter. In our functional magnetic resonance imaging study, participants were made to laugh by tickling in a first condition; in a second one they were requested to produce vocal utterances under the provocation of laughter by tickling. This investigation reveals increased neuronal activity in the sensorimotor cortex, the anterior cingulate gyrus, the insula, the nucleus accumbens, the hypothalamus and the periaqueductal grey for both conditions, thereby replicating the results of previous studies on ticklish laughter. However, further analysis indicates the activity in the emotion-associated regions to be lower when tickling is accompanied by voluntary vocalization. Here, a typical pattern of activation is identified, including the primary sensory cortex, a ventral area of the anterior insula and the ventral tegmental field, to which belongs to the nucleus ambiguus, namely, the common effector organ for voluntary and involuntary vocalizations. During the conflictual voluntary-vocalization versus laughter experience, the laughter-triggering network appears to rely heavily on a sensory and a deep interoceptive analysis, as well as on motor effectors in the brainstem. This article is part of the theme issue 'Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience'.

Motor constellation theory: A model of infants' phonological development

Every normally developing human infant solves the difficult problem of mapping their native-language phonology, but the neural mechanisms underpinning this behavior remain poorly understood. Here, motor constellation theory, an integrative neurophonological model, is presented, with the goal of explicating this issue. It is assumed that infants' motor-auditory phonological mapping takes place through infants' orosensory "reaching" for phonological elements observed in the language-specific ambient phonology, via reference to kinesthetic feedback from motor systems (e.g., articulators), and auditory feedback from resulting speech and speech-like sounds. Attempts are regulated by basal ganglion-cerebellar speech neural circuitry, and successful attempts at reproduction are enforced through dopaminergic signaling. Early in life, the pace of anatomical development constrains mapping such that complete language-specific phonological mapping is prohibited by infants' undeveloped supralaryngeal vocal tract and undescended larynx; constraints gradually dissolve with age, enabling adult phonology. Where appropriate, reference is made to findings from animal and clinical models. Some implications for future modeling and simulation efforts, as well as clinical settings, are also discussed.

Transcranial direct current stimulation over the primary motor cortex improves speech production in post-stroke dysarthric speakers: A randomized pilot study

PURPOSE

The current study investigated the therapeutic potential of transcranial direct current stimulation (tDCS) on speech intelligibility, speech-related physiological and vocal functions among post-stroke dysarthric patients.

METHOD

Nine chronic post-stroke dysarthric patients were randomly assigned to the stimulation or sham group. The stimulation group received 2mA of anodal tDCS over the left inferior primary motor cortex for 15 minutes, while the sham group received 30s of stimulation under the same settings. All the participants received 10 daily 15 minutes of individualized speech therapy targeting their dominant phonological process or phonemes with the greatest difficulty. The outcome measures included (1) perceptual analysis of single words, passage reading and diadochokinetic rate, (2) acoustic analysis of a sustained vowel, and (3) kinematic analysis of rapid syllable repetitions and syllable production in sentence, conducted before and after the treatment.

RESULTS

The results revealed that both the stimulation and sham groups had improved perceptual speech intelligibility at the word level, reduced short rushes of speech during passage reading, improved rate during alternating motion rate, AMR-kha1, and improved articulatory kinematics in AMR-tha1 and syllables /tha1/ and /kha1/ production in sentence. Compared to the sham group, the stimulation group showed significant improvement in articulatory kinematics in AMR-kha1 and syllable /kha1/ production in sentence. The findings also showed that anodal stimulation led to reduced shimmer value in sustained vowel /a/ phonation, positive changes in articulatory kinematics in AMR-tha1 and syllables /pha1/ and /kha1/ production in sentence at the post treatment measure. In addition to positive effects on articulatory control, reduced perturbation of voice amplitude documented in the stimulation group post treatment suggests possible tDCS effects on the vocal function.

CONCLUSIONS

The current study documented the beneficial effects of anodal tDCS over the primary motor cortex on speech production and suggested that combined tDCS and speech therapy may promote recovery from post-stroke dysarthria.

Continuous theta burst stimulation over left supplementary motor area facilitates auditory-vocal integration in individuals with Parkinson’s disease

Accumulating evidence suggests that impairment in auditory-vocal integration characterized by abnormally enhanced vocal compensations for auditory feedback perturbations contributes to hypokinetic dysarthria in Parkinson’s disease (PD). However, treatment of this abnormality remains a challenge. The present study examined whether abnormalities in auditory-motor integration for vocal pitch regulation in PD can be modulated by neuronavigated continuous theta burst stimulation (c-TBS) over the left supplementary motor area (SMA). After receiving active or sham c-TBS over left SMA, 16 individuals with PD vocalized vowel sounds while hearing their own voice unexpectedly pitch-shifted two semitones upward or downward. A group of pairwise-matched healthy participants was recruited as controls. Their vocal responses and event-related potentials (ERPs) were measured and compared across the conditions. The results showed that applying c-TBS over left SMA led to smaller vocal responses paralleled by smaller P1 and P2 responses and larger N1 responses in individuals with PD. Major neural generators of reduced P2 responses were located in the right inferior and medial frontal gyrus, pre- and post-central gyrus, and insula. Moreover, suppressed vocal compensations were predicted by reduced P2 amplitudes and enhanced N1 amplitudes. Notably, abnormally enhanced vocal and P2 responses in individuals with PD were normalized by c-TBS over left SMA when compared to healthy controls. Our results provide the first causal evidence that abnormalities in auditory-motor control of vocal pitch production in PD can be modulated by c-TBS over left SMA, suggesting that it may be a promising non-invasive treatment for speech motor disorders in PD.

Effects of Voiced Gargling on the Electrical Activity of Extrinsic Laryngeal Muscles and Vocal Self-assessment

OBJECTIVE

To verify the immediate effects of voiced gargling on the electrical activity of extrinsic laryngeal muscles and vocal self-assessment.

METHODS

A sample of 20 individuals of both sexes, mean age of 31.95 (±11.57) years, were equally divided in two groups according to the presence or absence of vocal complaint. Both groups were evaluated by surface electromyography of the suprahyoid (SH) and infrahyoid (IH) muscle areas during rest, phonation of the sustained vowel [Ɛ] in habitual and strong intensities; phonation of rising and falling glissando; and counting from 1 to 10. Surface electromyography was assessed before and after the voiced gargling exercise, which lasted 1 minute. All participants self-rated their voice and phonatory comfort after the exercise. Wilcoxon and Mann-Whitney tests were applied, as well as Fisher's exact test and linear-to-linear test. The level of significance was 5%.

RESULTS

The percentage of electrical activity of the SH muscle area decreased in the glissando and counting tasks in the group with vocal complaint, as well as in phonation of sustained vowel in strong intensity in the group without complaint. Decrease was also observed in the right IH muscle area at rest and during sustained vowel phonation at habitual and strong intensities. Percentage of muscular electrical activity was lower in the group with complaint in the following situations: IH muscle area on both sides, at rest and during habitual phonation of sustained vowel and glissando before and after the exercise; right IH muscle area, during counting and strong phonation of sustained vowel before and after exercise; left IH muscle area, in the counting task, just after intervention. Most participants noticed improvement in voice (70%) and phonatory comfort (65%).

CONCLUSIONS

Voiced gargling during 1 minute promotes immediate effects on the electrical activity of the extrinsic laryngeal muscles in individuals with or without vocal complaint. Most individuals reported improved voice and phonatory comfort after exercise.

LaDIVA: A neurocomputational model providing laryngeal motor control for speech acquisition and production

Many voice disorders are the result of intricate neural and/or biomechanical impairments that are poorly understood. The limited knowledge of their etiological and pathophysiological mechanisms hampers effective clinical management. Behavioral studies have been used concurrently with computational models to better understand typical and pathological laryngeal motor control. Thus far, however, a unified computational framework that quantitatively integrates physiologically relevant models of phonation with the neural control of speech has not been developed. Here, we introduce LaDIVA, a novel neurocomputational model with physiologically based laryngeal motor control. We combined the DIVA model (an established neural network model of speech motor control) with the extended body-cover model (a physics-based vocal fold model). The resulting integrated model, LaDIVA, was validated by comparing its model simulations with behavioral responses to perturbations of auditory vocal fundamental frequency (fo) feedback in adults with typical speech. LaDIVA demonstrated capability to simulate different modes of laryngeal motor control, ranging from short-term (i.e., reflexive) and long-term (i.e., adaptive) auditory feedback paradigms, to generating prosodic contours in speech. Simulations showed that LaDIVA's laryngeal motor control displays properties of motor equivalence, i.e., LaDIVA could robustly generate compensatory responses to reflexive vocal fo perturbations with varying initial laryngeal muscle activation levels leading to the same output. The model can also generate prosodic contours for studying laryngeal motor control in running speech. LaDIVA can expand the understanding of the physiology of human phonation to enable, for the first time, the investigation of causal effects of neural motor control in the fine structure of the vocal signal.

Impact of Startling Acoustic Stimuli on Word Repetition in Individuals With Aphasia and Apraxia of Speech Following Stroke

PURPOSE

The StartReact effect, whereby movements are elicited by loud, startling acoustic stimuli (SAS), allows the evaluation of movements when initiated through involuntary circuitry, before auditory feedback. When StartReact is applied during poststroke upper extremity movements, individuals exhibit increased muscle recruitment, reaction times, and reaching distances. StartReact releases unimpaired speech with similar increases in muscle recruitment and reaction time. However, as poststroke communication disorders have divergent neural circuitry from upper extremity tasks, it is unclear if StartReact will enhance speech poststroke. Our objective is to determine if (a) StartReact is present in individuals with poststroke aphasia and apraxia and (b) SAS exposure enhances speech intelligibility.

METHOD

We remotely delivered startling, 105-dB white noise bursts (SAS) and quiet, non-SAS cues to 15 individuals with poststroke aphasia and apraxia during repetition of six words. We evaluated average word intensity, pitch, pitch trajectories, vowel formants F1 and F2 (first and second formants), phonemic error rate, and percent incidence of each SAS versus non-SAS-elicited phoneme produced under each cue type.

RESULTS

For SAS trials compared to non-SAS, speech intensity increased (∆ + 0.6 dB), speech pitch increased (∆ + 22.7 Hz), and formants (F1 and F2) changed, resulting in a smaller vowel space after SAS. SAS affected pitch trajectories for some, but not all, words. Non-SAS trials had more stops (∆ + 4.7 utterances) while SAS trials had more sustained phonemes (fricatives, glides, affricates, liquids; ∆ + 5.4 utterances). SAS trials had fewer distortion errors but no change in substitution errors or overall error rate compared to non-SAS trials.

CONCLUSIONS

We show that stroke-impaired speech is susceptible to StartReact, evidenced by decreased intelligibility due to altered formants, pitch trajectories, and articulation, including increased incidence of sounds that could not be produced without SAS. Future studies should examine the impact of SAS on voluntary speech intelligibility and clinical measures of aphasia and apraxia.

Cortical basis for skilled vocalization

We examined the cortical control of a laryngeal muscle that is essential for vocalization in two monkey species that differ in their vocal motor skill. Our results suggest that enhancements in vocal skill are coupled to enlargements in the descending output from two premotor areas, ventral area 6 (area 6V) and the supplementary motor area (SMA). This result challenges the view that improvements in motor skills are due largely to changes in the output from the primary motor cortex.

Marmosets display remarkable vocal motor abilities. Macaques do not. What is it about the marmoset brain that enables its skill in the vocal domain? We examined the cortical control of a laryngeal muscle that is essential for vocalization in both species. We found that, in both monkeys, multiple premotor areas in the frontal lobe along with the primary motor cortex (M1) are major sources of disynaptic drive to laryngeal motoneurons. Two of the premotor areas, ventral area 6 (area 6V) and the supplementary motor area (SMA), are a substantially larger source of descending output in marmosets. We propose that the enhanced vocal motor skills of marmosets are due, in part, to the expansion of descending output from these premotor areas.

Faces and Voices Processing in Human and Primate Brains: Rhythmic and Multimodal Mechanisms Underlying the Evolution and Development of Speech

While influential works since the 1970s have widely assumed that imitation is an innate skill in both human and non-human primate neonates, recent empirical studies and meta-analyses have challenged this view, indicating other forms of reward-based learning as relevant factors in the development of social behavior. The visual input translation into matching motor output that underlies imitation abilities instead seems to develop along with social interactions and sensorimotor experience during infancy and childhood. Recently, a new visual stream has been identified in both human and non-human primate brains, updating the dual visual stream model. This third pathway is thought to be specialized for dynamics aspects of social perceptions such as eye-gaze, facial expression and crucially for audio-visual integration of speech. Here, we review empirical studies addressing an understudied but crucial aspect of speech and communication, namely the processing of visual orofacial cues (i.e., the perception of a speaker's lips and tongue movements) and its integration with vocal auditory cues. Along this review, we offer new insights from our understanding of speech as the product of evolution and development of a rhythmic and multimodal organization of sensorimotor brain networks, supporting volitional motor control of the upper vocal tract and audio-visual voices-faces integration.

Temporal specificity of abnormal neural oscillations during phonatory events in laryngeal dystonia

Laryngeal dystonia is a debilitating disorder of voicing in which the laryngeal muscles are intermittently in spasm resulting in involuntary interruptions during speech. The central pathophysiology of laryngeal dystonia, underlying computational impairments in vocal motor control, remains poorly understood. Although prior imaging studies have found aberrant activity in the CNS during phonation in patients with laryngeal dystonia, it is not known at what timepoints during phonation these abnormalities emerge and what function may be impaired. To investigate this question, we recruited 22 adductor laryngeal dystonia patients (15 female, age range = 28.83-72.46 years) and 18 controls (eight female, age range = 27.40-71.34 years). We leveraged the fine temporal resolution of magnetoencephalography to monitor neural activity around glottal movement onset, subsequent voice onset and after the onset of pitch feedback perturbations. We examined event-related beta-band (12-30 Hz) and high-gamma-band (65-150 Hz) neural oscillations. Prior to glottal movement onset, we observed abnormal frontoparietal motor preparatory activity. After glottal movement onset, we observed abnormal activity in the somatosensory cortex persisting through voice onset. Prior to voice onset and continuing after, we also observed abnormal activity in the auditory cortex and the cerebellum. After pitch feedback perturbation onset, we observed no differences between controls and patients in their behavioural responses to the perturbation. But in patients, we did find abnormal activity in brain regions thought to be involved in the auditory feedback control of vocal pitch (premotor, motor, somatosensory and auditory cortices). Our study results confirm the abnormal processing of somatosensory feedback that has been seen in other studies. However, there were several remarkable findings in our study. First, patients have impaired vocal motor activity even before glottal movement onset, suggesting abnormal movement preparation. These results are significant because (i) they occur before movement onset, abnormalities in patients cannot be ascribed to deficits in vocal performance and (ii) they show that neural abnormalities in laryngeal dystonia are more than just abnormal responses to sensory feedback during phonation as has been hypothesized in some previous studies. Second, abnormal auditory cortical activity in patients begins even before voice onset, suggesting abnormalities in setting up auditory predictions before the arrival of auditory feedback at voice onset. Generally, activation abnormalities identified in key brain regions within the speech motor network around various phonation events not only provide temporal specificity to neuroimaging phenotypes in laryngeal dystonia but also may serve as potential therapeutic targets for neuromodulation.

Functional Approaches to the Surgery of Brain Gliomas

In the surgery of gliomas, recent years have witnessed unprecedented theoretical and technical development, which extensively increased indication to surgery. On one hand, it has been solidly demonstrated the impact of gross total resection on life expectancy. On the other hand, the paradigm shift from classical cortical localization of brain function towards connectomics caused by the resurgence of awake surgery and the advent of tractography has permitted safer surgeries focused on subcortical white matter tracts preservation and allowed for surgical resections within regions, such as Broca's area or the primary motor cortex, which were previously deemed inoperable. Furthermore, new asleep electrophysiological techniques have been developed whenever awake surgery is not an option, such as operating in situations of poor compliance (including paediatric patients) or pre-existing neurological deficits. One such strategy is the use of intraoperative neurophysiological monitoring (IONM), enabling the identification and preservation of functionally defined, but anatomically ambiguous, cortico-subcortical structures through mapping and monitoring techniques. These advances tie in with novel challenges, specifically risk prediction and the impact of neuroplasticity, the indication for tumour resection beyond visible borders, or supratotal resection, and most of all, a reappraisal of the importance of the right hemisphere from early psychosurgery to mapping and preservation of social behaviour, executive control, and decision making.Here we review current advances and future perspectives in a functional approach to glioma surgery.

Vocal plasticity in harbour seal pups

Vocal plasticity can occur in response to environmental and biological factors, including conspecifics' vocalizations and noise. Pinnipeds are one of the few mammalian groups capable of vocal learning, and are therefore relevant to understanding the evolution of vocal plasticity in humans and other animals. Here, we investigate the vocal plasticity of harbour seals (Phoca vitulina), a species with vocal learning abilities observed in adulthood but not puppyhood. To evaluate early mammalian vocal development, we tested 1-3 weeks-old seal pups. We tailored noise playbacks to this species and age to induce seal pups to shift their fundamental frequency (f0), rather than adapt call amplitude or temporal characteristics. We exposed individual pups to low- and high-intensity bandpass-filtered noise, which spanned-and masked-their typical range of f0; simultaneously, we recorded pups' spontaneous calls. Unlike most mammals, pups modified their vocalizations by lowering their f0 in response to increased noise. This modulation was precise and adapted to the particular experimental manipulation of the noise condition. In addition, higher levels of noise induced less dispersion around the mean f0, suggesting that pups may have actively focused their phonatory efforts to target lower frequencies. Noise did not seem to affect call amplitude. However, one seal showed two characteristics of the Lombard effect known for human speech in noise: significant increase in call amplitude and flattening of spectral tilt. Our relatively low noise levels may have favoured f0 modulation while inhibiting amplitude adjustments. This lowering of f0 is unusual, as most animals commonly display no such f0 shift. Our data represent a relatively rare case in mammalian neonates, and have implications for the evolution of vocal plasticity and vocal learning across species, including humans. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

A dual larynx motor networks hypothesis

Humans are vocal modulators par excellence. This ability is supported in part by the dual representation of the laryngeal muscles in the motor cortex. Movement, however, is not the product of motor cortex alone but of a broader motor network. This network consists of brain regions that contain somatotopic maps that parallel the organization in motor cortex. We therefore present a novel hypothesis that the dual laryngeal representation is repeated throughout the broader motor network. In support of the hypothesis, we review existing literature that demonstrates the existence of network-wide somatotopy and present initial evidence for the hypothesis' plausibility. Understanding how this uniquely human phenotype in motor cortex interacts with broader brain networks is an important step toward understanding how humans evolved the ability to speak. We further suggest that this system may provide a means to study how individual components of the nervous system evolved within the context of neuronal networks. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

Singers show enhanced performance and neural representation of vocal imitation

Humans have a remarkable capacity to finely control the muscles of the larynx, via distinct patterns of cortical topography and innervation that may underpin our sophisticated vocal capabilities compared with non-human primates. Here, we investigated the behavioural and neural correlates of laryngeal control, and their relationship to vocal expertise, using an imitation task that required adjustments of larynx musculature during speech. Highly trained human singers and non-singer control participants modulated voice pitch and vocal tract length (VTL) to mimic auditory speech targets, while undergoing real-time anatomical scans of the vocal tract and functional scans of brain activity. Multivariate analyses of speech acoustics, larynx movements and brain activation data were used to quantify vocal modulation behaviour and to search for neural representations of the two modulated vocal parameters during the preparation and execution of speech. We found that singers showed more accurate task-relevant modulations of speech pitch and VTL (i.e. larynx height, as measured with vocal tract MRI) during speech imitation; this was accompanied by stronger representation of VTL within a region of the right somatosensory cortex. Our findings suggest a common neural basis for enhanced vocal control in speech and song. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

The multi-dimensional nature of vocal learning

How learning affects vocalizations is a key question in the study of animal communication and human language. Parallel efforts in birds and humans have taught us much about how vocal learning works on a behavioural and neurobiological level. Subsequent efforts have revealed a variety of cases among mammals in which experience also has a major influence on vocal repertoires. Janik and Slater (Anim. Behav.60, 1-11. (doi:10.1006/anbe.2000.1410)) introduced the distinction between vocal usage and production learning, providing a general framework to categorize how different types of learning influence vocalizations. This idea was built on by Petkov and Jarvis (Front. Evol. Neurosci.4, 12. (doi:10.3389/fnevo.2012.00012)) to emphasize a more continuous distribution between limited and more complex vocal production learners. Yet, with more studies providing empirical data, the limits of the initial frameworks become apparent. We build on these frameworks to refine the categorization of vocal learning in light of advances made since their publication and widespread agreement that vocal learning is not a binary trait. We propose a novel classification system, based on the definitions by Janik and Slater, that deconstructs vocal learning into key dimensions to aid in understanding the mechanisms involved in this complex behaviour. We consider how vocalizations can change without learning, and a usage learning framework that considers context specificity and timing. We identify dimensions of vocal production learning, including the copying of auditory models (convergence/divergence on model sounds, accuracy of copying), the degree of change (type and breadth of learning) and timing (when learning takes place, the length of time it takes and how long it is retained). We consider grey areas of classification and current mechanistic understanding of these behaviours. Our framework identifies research needs and will help to inform neurobiological and evolutionary studies endeavouring to uncover the multi-dimensional nature of vocal learning. This article is part of the theme issue 'Vocal learning in animals and humans'.

Shouting strengthens maximal voluntary force and is associated with augmented pupillary dilation

Previous research has demonstrated that human maximal voluntary force is generally limited by neural inhibition. Producing a shout during maximal exertion effort enhances the force levels of maximal voluntary contraction. However, the mechanisms underlying this enhancement effect on force production remain unclear. We investigated the influence of producing a shout on the pupil-linked neuromodulatory system state by examining pupil size. We also examined its effects on the motor system state by examining motor evoked potentials in response to transcranial magnetic stimulation applied over the contralateral primary motor cortex, and by evaluating handgrip maximal voluntary force. Analysis revealed that producing a shout significantly increased handgrip maximal voluntary force, followed by an increase in pupil size and a reduction of the cortical silent period. Our results indicate that producing a shout increased handgrip maximal voluntary force through the enhancement of motor cortical excitability, possibly via the enhancement of noradrenergic system activity. This study provides evidence that the muscular force-enhancing effect of shouting during maximal force exertion is related to both the motor system state and the pupil-linked neuromodulatory system state.

Phonatory Characteristics of Male Patients with Classic Essential Tremor

OBJECTIVE

Voice tremor (VT) is one of the characteristics of essential tremor (ET). This study was designed to describe the group and phonatory characteristics of classic ET patients with VT.

METHODS

This retrospective case-control study compared classic ET patients with age and sex-matched controls. The ET population was subgrouped based on auditory perceptual voice analysis. Electroglottography and acoustic voice samples obtained from both groups were analyzed for contact quotient (CQ) and multidimensional voice program parameters, i.e., fundamental frequency (F0), perturbation, noise, and tremor parameters.

RESULTS

The CQ, F0, perturbation, noise, and tremor characteristics significantly increased from the moderate VT group to the severe VT group.

CONCLUSION

The CQ, F0, and noise characteristics reflected the vocal folds' functionality. The perturbation and tremor parameters variation were reasoned considering the tremor-related changes occurring in the laryngeal, vocal tract, and expiratory muscles in patients with ET. Thus, phonatory analysis may help in monitoring the progression of ET.

Five Breakthroughs: A First Approximation of Brain Evolution From Early Bilaterians to Humans

Retracing the evolutionary steps by which human brains evolved can offer insights into the underlying mechanisms of human brain function as well as the phylogenetic origin of various features of human behavior. To this end, this article presents a model for interpreting the physical and behavioral modifications throughout major milestones in human brain evolution. This model introduces the concept of a "breakthrough" as a useful tool for interpreting suites of brain modifications and the various adaptive behaviors these modifications enabled. This offers a unique view into the ordered steps by which human brains evolved and suggests several unique hypotheses on the mechanisms of human brain function.

Songbirds can learn flexible contextual control over syllable sequencing

The flexible control of sequential behavior is a fundamental aspect of speech, enabling endless reordering of a limited set of learned vocal elements (syllables or words). Songbirds are phylogenetically distant from humans but share both the capacity for vocal learning and neural circuitry for vocal control that includes direct pallial-brainstem projections. Based on these similarities, we hypothesized that songbirds might likewise be able to learn flexible, moment-by-moment control over vocalizations. Here, we demonstrate that Bengalese finches (Lonchura striata domestica), which sing variable syllable sequences, can learn to rapidly modify the probability of specific sequences (e.g. ‘ab-c’ versus ‘ab-d’) in response to arbitrary visual cues. Moreover, once learned, this modulation of sequencing occurs immediately following changes in contextual cues and persists without external reinforcement. Our findings reveal a capacity in songbirds for learned contextual control over syllable sequencing that parallels human cognitive control over syllable sequencing in speech.

Human speech and birdsong share numerous parallels. Both humans and birds learn their vocalizations during critical phases early in life, and both learn by imitating adults. Moreover, both humans and songbirds possess specific circuits in the brain that connect the forebrain to midbrain vocal centers.

Humans can flexibly control what they say and how by reordering a fixed set of syllables into endless combinations, an ability critical to human speech and language. Birdsongs also vary depending on their context, and melodies to seduce a mate will be different from aggressive songs to warn other males to stay away. However, so far it was unclear whether songbirds are also capable of modifying songs independent of social or other naturally relevant contexts.

To test whether birds can control their songs in a purposeful way, Veit et al. trained adult male Bengalese finches to change the sequence of their songs in response to random colored lights that had no natural meaning to the birds. A specific computer program was used to detect different variations on a theme that the bird naturally produced (for example, “ab-c” versus “ab-d”), and rewarded birds for singing one sequence when the light was yellow, and the other when it was green. Gradually, the finches learned to modify their songs and were able to switch between the appropriate sequences as soon as the light cues changed. This ability persisted for days, even without any further training.

This suggests that songbirds can learn to flexibly and purposefully modify the way in which they sequence the notes in their songs, in a manner that parallels how humans control syllable sequencing in speech. Moreover, birds can learn to do this ‘on command’ in response to an arbitrarily chosen signal, even if it is not something that would impact their song in nature.

Songbirds are an important model to study brain circuits involved in vocal learning. They are one of the few animals that, like humans, learn their vocalizations by imitating conspecifics. The finding that they can also flexibly control vocalizations may help shed light on the interactions between cognitive processing and sophisticated vocal learning abilities.

Thalamic Deep Brain Stimulation for Spasmodic Dysphonia: A Phase I Prospective Randomized Double-Blind Crossover Trial

BACKGROUND

Adductor spasmodic dysphonia (SD) is a dystonia of the vocal folds causing difficulty with speech. The current standard of care is repeated botulinum toxin injections to weaken the adductor muscles. We sought to ameliorate the underlying neurological cause of SD with a novel therapy—deep brain stimulation (DBS).

OBJECTIVE

To assess the safety of DBS in SD through phase I trial, and to quantify the magnitude of any benefit.

METHODS

Six patients had left ventral intermediate nucleus (Vim) thalamic DBS and were randomized to 3 mo blinded-DBS “on” or “off” followed by a crossover. Primary outcomes were quality of life and quality of voice during the blinded phase. Patients continued with open-DBS “on.” Secondary outcomes were comparisons of pre- and 1-yr cognitive, mood, and quality of life. This trial was registered with ClinicalTrials.gov (NCT02558634).

RESULTS

There were no complications. Every patient reported an improvement in quality of life (P = .07) and had an improvement in quality of their voice (P = .06) when their blinded DBS was “on” versus “off.” The trend did not reach statistical significance with the small sample size. Secondary outcomes showed no difference in cognition, an improvement in mood, and quality of life at 1 yr.

CONCLUSION

This phase I randomized controlled trial confirmed that DBS can be performed safely in patients with SD. Blinded DBS produced a strong trend toward improved quality of life and objective quality of voice despite the small sample size. The cerebellar circuit, not the pallidal circuit, appears to be crucial for motor control of the vocal folds.

The Dynamics of Speech Motor Control Revealed with Time-Resolved fMRI

Holding a conversation means that speech must be started, maintained, and stopped continuously. The brain networks that underlie these aspects of speech motor control remain poorly understood. Here we collected functional magnetic resonance imaging (fMRI) data while participants produced normal and fast rate speech in response to sequences of visually presented objects. We took a non-conventional approach to fMRI data analysis that allowed us to study speech motor behavior as it unfolded over time. To this end, whole-brain fMRI signals were extracted in stimulus-locked epochs using slice-based fMRI. These data were then subjected to group independent component analysis to discover spatially independent networks that were associated with different temporal activation profiles. The results revealed two basic brain networks with different temporal dynamics: a cortical network that was activated continuously during speech production, and a second cortico-subcortical network that increased in activity during the initiation and suppression of speech production. Additional analyses explored whether key areas involved in motor suppression such as the right inferior frontal gyrus, sub-thalamic nucleus and pre-supplementary motor area provide first-order signals to stop speech. The results reveal for the first time the brain networks associated with the initiation, maintenance, and suppression of speech motor behavior.

Common fronto-temporal effective connectivity in humans and monkeys

Human brain pathways supporting language and declarative memory are thought to have differentiated substantially during evolution. However, cross-species comparisons are missing on site-specific effective connectivity between regions important for cognition. We harnessed functional imaging to visualize the effects of direct electrical brain stimulation in macaque monkeys and human neurosurgery patients. We discovered comparable effective connectivity between caudal auditory cortex and both ventro-lateral prefrontal cortex (VLPFC, including area 44) and parahippocampal cortex in both species. Human-specific differences were clearest in the form of stronger hemispheric lateralization effects. In humans, electrical tractography revealed remarkably rapid evoked potentials in VLPFC following auditory cortex stimulation and speech sounds drove VLPFC, consistent with prior evidence in monkeys of direct auditory cortex projections to homologous vocalization-responsive regions. The results identify a common effective connectivity signature in human and nonhuman primates, which from auditory cortex appears equally direct to VLPFC and indirect to the hippocampus. VIDEO ABSTRACT.

Nonverbal auditory communication - Evidence for integrated neural systems for voice signal production and perception

While humans have developed a sophisticated and unique system of verbal auditory communication, they also share a more common and evolutionarily important nonverbal channel of voice signaling with many other mammalian and vertebrate species. This nonverbal communication is mediated and modulated by the acoustic properties of a voice signal, and is a powerful - yet often neglected - means of sending and perceiving socially relevant information. From the viewpoint of dyadic (involving a sender and a signal receiver) voice signal communication, we discuss the integrated neural dynamics in primate nonverbal voice signal production and perception. Most previous neurobiological models of voice communication modelled these neural dynamics from the limited perspective of either voice production or perception, largely disregarding the neural and cognitive commonalities of both functions. Taking a dyadic perspective on nonverbal communication, however, it turns out that the neural systems for voice production and perception are surprisingly similar. Based on the interdependence of both production and perception functions in communication, we first propose a re-grouping of the neural mechanisms of communication into auditory, limbic, and paramotor systems, with special consideration for a subsidiary basal-ganglia-centered system. Second, we propose that the similarity in the neural systems involved in voice signal production and perception is the result of the co-evolution of nonverbal voice production and perception systems promoted by their strong interdependence in dyadic interactions.

High-density intracranial recordings reveal a distinct site in anterior dorsal precentral cortex that tracks perceived speech

Various brain regions are implicated in speech processing, and the specific function of some of them is better understood than others. In particular, involvement of the dorsal precentral cortex (dPCC) in speech perception remains debated, and attribution of the function of this region is more or less restricted to motor processing. In this study, we investigated high-density intracranial responses to speech fragments of a feature film, aiming to determine whether dPCC is engaged in perception of continuous speech. Our findings show that dPCC exhibited preference to speech over other tested sounds. Moreover, the identified area was involved in tracking of speech auditory properties including speech spectral envelope, its rhythmic phrasal pattern and pitch contour. DPCC also showed the ability to filter out noise from the perceived speech. Comparing these results to data from motor experiments showed that the identified region had a distinct location in dPCC, anterior to the hand motor area and superior to the mouth articulator region. The present findings uncovered with high-density intracranial recordings help elucidate the functional specialization of PCC and demonstrate the unique role of its anterior dorsal region in continuous speech perception.

Impaired Cortical Cytoarchitecture and Reduced Excitability of Deep-Layer Neurons in the Offspring of Diabetic Rats

Maternal diabetes has been related to low verbal task scores, impaired fine and gross motor skills, and poor performance in graphic and visuospatial tasks during childhood. The primary motor cortex is important for controlling motor functions, and embryos exposed to high glucose show changes in cell proliferation, migration, and differentiation during corticogenesis. However, the existing studies do not discriminate between embryos with or without neural tube defects, making it difficult to conclude whether the reported changes are related to neural tube defects or other anomalies. Furthermore, postnatal effects on central nervous system cytoarchitecture and function have been scarcely addressed. Through molecular, biochemical, morphological, and electrophysiological approaches, we provide evidence of impaired primary motor cerebral cortex lamination and neuronal function in pups from diabetic rats, showing an altered distribution of SATB2, FOXP2, and TBR1, impaired cell migration and polarity, and decreased excitability of deep-layer cortical neurons, suggesting abnormalities in cortico-cortical and extra-cortical innervation. Furthermore, phase-plot analysis of action potentials suggests changes in the activity of potassium channels. These results indicate that high-glucose insult during development promotes complex changes in migration, neurogenesis, cell polarity establishment, and dendritic arborization, which in turn lead to reduced excitability of deep-layer cortical neurons.

Vocomotor and Social Brain Networks Work Together to Express Social Traits in Voices

Voice modulation is important when navigating social interactions-tone of voice in a business negotiation is very different from that used to comfort an upset child. While voluntary vocal behavior relies on a cortical vocomotor network, social voice modulation may require additional social cognitive processing. Using functional magnetic resonance imaging, we investigated the neural basis for social vocal control and whether it involves an interplay of vocal control and social processing networks. Twenty-four healthy adult participants modulated their voice to express social traits along the dimensions of the social trait space (affiliation and competence) or to express body size (control for vocal flexibility). Naïve listener ratings showed that vocal modulations were effective in evoking social trait ratings along the two primary dimensions of the social trait space. Whereas basic vocal modulation engaged the vocomotor network, social voice modulation specifically engaged social processing regions including the medial prefrontal cortex, superior temporal sulcus, and precuneus. Moreover, these regions showed task-relevant modulations in functional connectivity to the left inferior frontal gyrus, a core vocomotor control network area. These findings highlight the impact of the integration of vocal motor control and social information processing for socially meaningful voice modulation.

Limbic and cortical control of phonation for speech in response to a public speech preparation stressor

Knowledge on brain networks subserving vocalization in vocally healthy individuals under various task conditions is scarce but paramount to understand voice disorders. The aims of our study were to determine (1) the effect of social-evaluative stress on the central neural control of phonation underlying speech production; and (2) the neural signature, personality profile, and aerodynamic vocal function in relation to salivary cortisol responses. Thirteen vocally healthy females underwent an event-related sparse-sampling fMRI protocol consisting of voiced and whispered sentence productions with and without exposure to the social-evaluative stressor public speaking anticipation. Participants completed a personality questionnaire, rating scales of negative emotional state, and provided salivary cortisol samples. In the total sample, the task contrast of voiced productions revealed that stressor exposure resulted in a peak activation in the right caudate with concomitant deactivations in the bilateral pgACC and aMCC, and right IFG, BA 9, BA 10, insula, putamen, and thalamus. There were individual differences in stressor-induced brain activations as a function of stress reactivity with greater cortisol reactivity linked with lower laryngeal motor cortex activity and lower scores on aspects of extraversion. Our data confirm that stress alters the phonatory control for speech production through limbic-motor interactions. The findings support the Trait Theory of Voice Disorders (Roy and Bless 2000) and help provide critical insights to the study of voice disorders such as primary muscle tension dysphonia.