A probabilistic map of the human ventral sensorimotor cortex using electrical stimulation

Dynamic functional connectivity in verbal cognitive control and word reading

Cognitive control processes enable the suppression of automatic behaviors and the initiation of appropriate responses. The Stroop color naming task serves as a benchmark paradigm for understanding the neurobiological model of verbal cognitive control. Previous research indicates a predominant engagement of the prefrontal and premotor cortex during the Stroop task compared to reading. We aim to further this understanding by creating a dynamic atlas of task-preferential modulations of functional connectivity through white matter. Patients undertook word-reading and Stroop tasks during intracranial EEG recording. We quantified task-related high-gamma amplitude modulations at 547 nonepileptic electrode sites, and a mixed model analysis identified regions and timeframes where these amplitudes differed between tasks. We then visualized white matter pathways with task-preferential functional connectivity enhancements at given moments. Word reading, compared to the Stroop task, exhibited enhanced functional connectivity in inter- and intra-hemispheric white matter pathways from the left occipital-temporal region 350-600 ms before response, including the posterior callosal fibers as well as the left vertical occipital, inferior longitudinal, inferior fronto-occipital, and arcuate fasciculi. The Stroop task showed enhanced functional connectivity in the pathways from the left middle-frontal pre-central gyri, involving the left frontal u-fibers and anterior callosal fibers. Automatic word reading largely utilizes the left occipital-temporal cortices and associated white matter tracts. Verbal cognitive control predominantly involves the left middle frontal and precentral gyri and its connected pathways. Our dynamic tractography atlases may serve as a novel resource providing insights into the unique neural dynamics and pathways of automatic reading and verbal cognitive control.

An instantaneous voice synthesis neuroprosthesis

Brain computer interfaces (BCIs) have the potential to restore communication to people who have lost the ability to speak due to neurological disease or injury. BCIs have been used to translate the neural correlates of attempted speech into text1-3. However, text communication fails to capture the nuances of human speech such as prosody, intonation and immediately hearing one's own voice. Here, we demonstrate a "brain-to-voice" neuroprosthesis that instantaneously synthesizes voice with closed-loop audio feedback by decoding neural activity from 256 microelectrodes implanted into the ventral precentral gyrus of a man with amyotrophic lateral sclerosis and severe dysarthria. We overcame the challenge of lacking ground-truth speech for training the neural decoder and were able to accurately synthesize his voice. Along with phonemic content, we were also able to decode paralinguistic features from intracortical activity, enabling the participant to modulate his BCI-synthesized voice in real-time to change intonation, emphasize words, and sing short melodies. These results demonstrate the feasibility of enabling people with paralysis to speak intelligibly and expressively through a BCI.

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".

Sensorimotor regulation of facial expression - An untouched frontier

Facial expression is a critical form of nonverbal social communication which promotes emotional exchange and affiliation among humans. Facial expressions are generated via precise contraction of the facial muscles, guided by sensory feedback. While the neural pathways underlying facial motor control are well characterized in humans and primates, it remains unknown how tactile and proprioceptive information reaches these pathways to guide facial muscle contraction. Thus, despite the importance of facial expressions for social functioning, little is known about how they are generated as a unique sensorimotor behavior. In this review, we highlight current knowledge about sensory feedback from the face and how it is distinct from other body regions. We describe connectivity between the facial sensory and motor brain systems, and call attention to the other brain systems which influence facial expression behavior, including vision, gustation, emotion, and interoception. Finally, we petition for more research on the sensory basis of facial expressions, asserting that incomplete understanding of sensorimotor mechanisms is a barrier to addressing atypical facial expressivity in clinical populations.

Stimulation of caudal inferior and middle frontal gyri disrupts planning during spoken interaction

Turn-taking is a central feature of conversation across languages and cultures.1,2,3,4 This key social behavior requires numerous sensorimotor and cognitive operations1,5,6 that can be organized into three general phases: comprehension of a partner's turn, preparation of a speaker's own turn, and execution of that turn. Using intracranial electrocorticography, we recently demonstrated that neural activity related to these phases is functionally distinct during turn-taking.7 In particular, networks active during the perceptual and articulatory stages of turn-taking consisted of structures known to be important for speech-related sensory and motor processing,8,9,10,11,12,13,14,15,16,17 while putative planning dynamics were most regularly observed in the caudal inferior frontal gyrus (cIFG) and the middle frontal gyrus (cMFG). To test if these structures are necessary for planning during spoken interaction, we used direct electrical stimulation (DES) to transiently perturb cortical function in neurosurgical patient-volunteers performing a question-answer task.7,18,19 We found that stimulating the cIFG and cMFG led to various response errors9,13,20,21 but not gross articulatory deficits, which instead resulted from DES of structures involved in motor control8,13,20,22 (e.g., the precentral gyrus). Furthermore, perturbation of the cIFG and cMFG delayed inter-speaker timing-consistent with slowed planning-while faster responses could result from stimulation of sites located in other areas. Taken together, our findings suggest that the cIFG and cMFG contain critical preparatory circuits that are relevant for interactive language use.

Processing of auditory feedback in perisylvian and insular cortex

When we speak, we not only make movements with our mouth, lips, and tongue, but we also hear the sound of our own voice. Thus, speech production in the brain involves not only controlling the movements we make, but also auditory and sensory feedback. Auditory responses are typically suppressed during speech production compared to perception, but how this manifests across space and time is unclear. Here we recorded intracranial EEG in seventeen pediatric, adolescent, and adult patients with medication-resistant epilepsy who performed a reading/listening task to investigate how other auditory responses are modulated during speech production. We identified onset and sustained responses to speech in bilateral auditory cortex, with a selective suppression of onset responses during speech production. Onset responses provide a temporal landmark during speech perception that is redundant with forward prediction during speech production. Phonological feature tuning in these "onset suppression" electrodes remained stable between perception and production. Notably, the posterior insula responded at sentence onset for both perception and production, suggesting a role in multisensory integration during feedback control.

The Feel of Speech: Multisystem and Polymodal Somatosensation in Speech Production

PURPOSE

The oral structures such as the tongue and lips have remarkable somatosensory capacities, but understanding the roles of somatosensation in speech production requires a more comprehensive knowledge of somatosensation in the speech production system in its entirety, including the respiratory, laryngeal, and supralaryngeal subsystems. This review was conducted to summarize the system-wide somatosensory information available for speech production.

METHOD

The search was conducted with PubMed/Medline and Google Scholar for articles published until November 2023. Numerous search terms were used in conducting the review, which covered the topics of psychophysics, basic and clinical behavioral research, neuroanatomy, and neuroscience.

RESULTS AND CONCLUSIONS

The current understanding of speech somatosensation rests primarily on the two pillars of psychophysics and neuroscience. The confluence of polymodal afferent streams supports the development, maintenance, and refinement of speech production. Receptors are both canonical and noncanonical, with the latter occurring especially in the muscles innervated by the facial nerve. Somatosensory representation in the cortex is disproportionately large and provides for sensory interactions. Speech somatosensory function is robust over the lifespan, with possible declines in advanced aging. The understanding of somatosensation in speech disorders is largely disconnected from research and theory on speech production. A speech somatoscape is proposed as the generalized, system-wide sensation of speech production, with implications for speech development, speech motor control, and speech disorders.

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.

A frontal cortical network is critical for language planning during spoken interaction

Many brain areas exhibit activity correlated with language planning, but the impact of these dynamics on spoken interaction remains unclear. Here we use direct electrical stimulation to transiently perturb cortical function in neurosurgical patient-volunteers performing a question-answer task. Stimulating structures involved in speech motor function evoked diverse articulatory deficits, while perturbations of caudal inferior and middle frontal gyri - which exhibit preparatory activity during conversational turn-taking - led to response errors. Perturbation of the same planning-related frontal regions slowed inter-speaker timing, while faster responses could result from stimulation of sites located in other areas. Taken together, these findings further indicate that caudal inferior and middle frontal gyri constitute a critical planning network essential for interactive language use.

A high-performance neuroprosthesis for speech decoding and avatar control

Speech neuroprostheses have the potential to restore communication to people living with paralysis, but naturalistic speed and expressivity are elusive1. Here we use high-density surface recordings of the speech cortex in a clinical-trial participant with severe limb and vocal paralysis to achieve high-performance real-time decoding across three complementary speech-related output modalities: text, speech audio and facial-avatar animation. We trained and evaluated deep-learning models using neural data collected as the participant attempted to silently speak sentences. For text, we demonstrate accurate and rapid large-vocabulary decoding with a median rate of 78 words per minute and median word error rate of 25%. For speech audio, we demonstrate intelligible and rapid speech synthesis and personalization to the participant's pre-injury voice. For facial-avatar animation, we demonstrate the control of virtual orofacial movements for speech and non-speech communicative gestures. The decoders reached high performance with less than two weeks of training. Our findings introduce a multimodal speech-neuroprosthetic approach that has substantial promise to restore full, embodied communication to people living with severe paralysis.

Beyond Broca: neural architecture and evolution of a dual motor speech coordination system

Classical neural architecture models of speech production propose a single system centred on Broca's area coordinating all the vocal articulators from lips to larynx. Modern evidence has challenged both the idea that Broca's area is involved in motor speech coordination and that there is only one coordination network. Drawing on a wide range of evidence, here we propose a dual speech coordination model in which laryngeal control of pitch-related aspects of prosody and song are coordinated by a hierarchically organized dorsolateral system while supralaryngeal articulation at the phonetic/syllabic level is coordinated by a more ventral system posterior to Broca's area. We argue further that these two speech production subsystems have distinguishable evolutionary histories and discuss the implications for models of language evolution.

A Neurosurgical Functional Dissection of the Middle Precentral Gyrus during Speech Production

Classical models have traditionally focused on the left posterior inferior frontal gyrus (Broca's area) as a key region for motor planning of speech production. However, converging evidence suggests that it is not critical for either speech motor planning or execution. Alternative cortical areas supporting high-level speech motor planning have yet to be defined. In this review, we focus on the precentral gyrus, whose role in speech production is often thought to be limited to lower-level articulatory muscle control. In particular, we highlight neurosurgical investigations that have shed light on a cortical region anatomically located near the midpoint of the precentral gyrus, hence called the middle precentral gyrus (midPrCG). The midPrCG is functionally located between dorsal hand and ventral orofacial cortical representations and exhibits unique sensorimotor and multisensory functions relevant for speech processing. This includes motor control of the larynx, auditory processing, as well as a role in reading and writing. Furthermore, direct electrical stimulation of midPrCG can evoke complex movements, such as vocalization, and selective injury can cause deficits in verbal fluency, such as pure apraxia of speech. Based on these findings, we propose that midPrCG is essential to phonological-motoric aspects of speech production, especially syllabic-level speech sequencing, a role traditionally ascribed to Broca's area. The midPrCG is a cortical brain area that should be included in contemporary models of speech production with a unique role in speech motor planning and execution.

Electrical stimulation-induced speech-related negative motor responses in the lateral frontal cortex

OBJECTIVE

Speech arrest is a common but crucial negative motor response (NMR) recorded during intraoperative brain mapping. However, recent studies have reported nonspeech-specific NMR sites in the ventral precentral gyrus (vPrCG), where stimulation halts both speech and ongoing hand movement. The aim of this study was to investigate the spatial relationship between speech-specific NMR sites and nonspeech-specific NMR sites in the lateral frontal cortex.

METHODS

In this prospective cohort study, an intraoperative mapping strategy was designed to identify positive motor response (PMR) sites and NMR sites in 33 consecutive patients undergoing awake craniotomy for the treatment of left-sided gliomas. Patients were asked to count, flex their hands, and simultaneously perform these two tasks to map NMRs. Each site was plotted onto a standard atlas and further analyzed. The speech and hand motor arrest sites in the supplementary motor area of 2 patients were resected. The 1- and 3-month postoperative language and motor functions of all patients were assessed.

RESULTS

A total of 91 PMR sites and 72 NMR sites were identified. NMR and PMR sites were anteroinferiorly and posterosuperiorly distributed in the precentral gyrus, respectively. Three distinct NMR sites were identified: 24 pure speech arrest (speech-specific NMR) sites (33.33%), 7 pure hand motor arrest sites (9.72%), and 41 speech and hand motor arrest (nonspeech-specific NMR) sites (56.94%). Nonspeech-specific NMR sites and speech-specific NMR sites were dorsoventrally distributed in the vPrCG. For language function, 1 of 2 patients in the NMA resection group had language dysfunction at the 1-month follow-up but had recovered by the 3-month follow-up. All patients in the NMA resection group had fine motor dysfunction at the 1- and 3-month follow-ups.

CONCLUSIONS

The study results demonstrated a functional segmentation of speech-related NMRs in the lateral frontal cortex and that most of the stimulation-induced speech arrest sites are not specific to speech. A better understanding of the spatial distribution of speech-related NMR sites will be helpful in surgical planning and intraoperative mapping and provide in-depth insight into the motor control of speech production.

Beyond language: The unspoken sensory-motor representation of the tongue in non-primates, non-human and human primates

The English idiom "on the tip of my tongue" commonly acknowledges that something is known, but it cannot be immediately brought to mind. This phrase accurately describes sensorimotor functions of the tongue, which are fundamental for many tongue-related behaviors (e.g., speech), but often neglected by scientific research. Here, we review a wide range of studies conducted on non-primates, non-human and human primates with the aim of providing a comprehensive description of the cortical representation of the tongue's somatosensory inputs and motor outputs across different phylogenetic domains. First, we summarize how the properties of passive non-noxious mechanical stimuli are encoded in the putative somatosensory tongue area, which has a conserved location in the ventral portion of the somatosensory cortex across mammals. Second, we review how complex self-generated actions involving the tongue are represented in more anterior regions of the putative somato-motor tongue area. Finally, we describe multisensory response properties of the primate and non-primate tongue area by also defining how the cytoarchitecture of this area is affected by experience and deafferentation.

Comparative morphology and physiology of the vocal production apparatus and the brain in the extant primates

Objective data mainly from the comparative anatomy of various organs related to human speech and language is considered to unearth clues about the mechanisms behind language development. The two organs of the larynx and hyoid bone are considered to have evolved towards suitable positions and forms in preparation for the occurrence of the large repertoire of vocalization necessary for human speech. However, some researchers have asserted that there is no significant difference of these organs between humans and non-human primates. Speech production is dependent on the voluntary control of the respiratory, laryngeal, and vocal tract musculature. Such control is fully present in humans but only partially so in non-human primates, which appear to be able to voluntarily control only supralaryngeal articulators. Both humans and non-human primates have direct cortical innervation of motor neurons controlling the supralaryngeal vocal tract but only human appear to have direct cortical innervation of motor neurons controlling the larynx. In this review, we investigate the comparative morphology and function of the wide range of components involved in vocal production, including the larynx, the hyoid bone, the tongue, and the vocal brain. We would like to emphasize the importance of the tongue in the primary development of human speech and language. It is now time to reconsider the possibility of the tongue playing a definitive role in the emergence of human speech.

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.

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)'.

Speech-Driven Spectrotemporal Receptive Fields Beyond the Auditory Cortex

We recently developed a method to estimate speech-driven spectrotemporal receptive fields (STRFs) using fMRI. The method uses spectrotemporal modulation filtering, a form of acoustic distortion that renders speech sometimes intelligible and sometimes unintelligible. Using this method, we found significant STRF responses only in classic auditory regions throughout the superior temporal lobes. However, our analysis was not optimized to detect small clusters of STRFs as might be expected in non-auditory regions. Here, we re-analyze our data using a more sensitive multivariate statistical test for cross-subject alignment of STRFs, and we identify STRF responses in non-auditory regions including the left dorsal premotor cortex (dPM), left inferior frontal gyrus (IFG), and bilateral calcarine sulcus (calcS). All three regions responded more to intelligible than unintelligible speech, but left dPM and calcS responded significantly to vocal pitch and demonstrated strong functional connectivity with early auditory regions. Left dPM's STRF generated the best predictions of activation on trials rated as unintelligible by listeners, a hallmark auditory profile. IFG, on the other hand, responded almost exclusively to intelligible speech and was functionally connected with classic speech-language regions in the superior temporal sulcus and middle temporal gyrus. IFG's STRF was also (weakly) able to predict activation on unintelligible trials, suggesting the presence of a partial 'acoustic trace' in the region. We conclude that left dPM is part of the human dorsal laryngeal motor cortex, a region previously shown to be capable of operating in an 'auditory mode' to encode vocal pitch. Further, given previous observations that IFG is involved in syntactic working memory and/or processing of linear order, we conclude that IFG is part of a higher-order speech circuit that exerts a top-down influence on processing of speech acoustics. Finally, because calcS is modulated by emotion, we speculate that changes in the quality of vocal pitch may have contributed to its response.

Articulatory Gain Predicts Motor Cortex and Subthalamic Nucleus Activity During Speech

Speaking precisely is important for effective verbal communication, and articulatory gain is one component of speech motor control that contributes to achieving this goal. Given that the basal ganglia have been proposed to regulate the speed and size of limb movement, that is, movement gain, we explored the basal ganglia contribution to articulatory gain, through local field potentials (LFP) recorded simultaneously from the subthalamic nucleus (STN), precentral gyrus, and postcentral gyrus. During STN deep brain stimulation implantation for Parkinson's disease, participants read aloud consonant-vowel-consonant syllables. Articulatory gain was indirectly assessed using the F2 Ratio, an acoustic measurement of the second formant frequency of/i/vowels divided by/u/vowels. Mixed effects models demonstrated that the F2 Ratio correlated with alpha and theta activity in the precentral gyrus and STN. No correlations were observed for the postcentral gyrus. Functional connectivity analysis revealed that higher phase locking values for beta activity between the STN and precentral gyrus were correlated with lower F2 Ratios, suggesting that higher beta synchrony impairs articulatory precision. Effects were not related to disease severity. These data suggest that articulatory gain is encoded within the basal ganglia-cortical loop.

Human larynx motor cortices coordinate respiration for vocal-motor control

Vocal flexibility is a hallmark of the human species, most particularly the capacity to speak and sing. This ability is supported in part by the evolution of a direct neural pathway linking the motor cortex to the brainstem nucleus that controls the larynx the primary sound source for communication. Early brain imaging studies demonstrated that larynx motor cortex at the dorsal end of the orofacial division of motor cortex (dLMC) integrated laryngeal and respiratory control, thereby coordinating two major muscular systems that are necessary for vocalization. Neurosurgical studies have since demonstrated the existence of a second larynx motor area at the ventral extent of the orofacial motor division (vLMC) of motor cortex. The vLMC has been presumed to be less relevant to speech motor control, but its functional role remains unknown. We employed a novel ultra-high field (7T) magnetic resonance imaging paradigm that combined singing and whistling simple melodies to localise the larynx motor cortices and test their involvement in respiratory motor control. Surprisingly, whistling activated both 'larynx areas' more strongly than singing despite the reduced involvement of the larynx during whistling. We provide further evidence for the existence of two larynx motor areas in the human brain, and the first evidence that laryngeal-respiratory integration is a shared property of both larynx motor areas. We outline explicit predictions about the descending motor pathways that give these cortical areas access to both the laryngeal and respiratory systems and discuss the implications for the evolution of speech.

A Novel Intraoperative Brain Mapping Integrated Task-Presentation Platform

BACKGROUND

To be efficient, intraoperative task-presentation systems must accurately present various language and cognitive tasks to patients undergoing awake surgery, and record behavioral data without compromising convenience of surgery.

OBJECTIVE

To present an integrated brain mapping task-presentation system we developed and evaluate its effectiveness in intraoperative task presentation.

METHODS

The Brain Mapping Interactive Stimulation System (Brain MISS) is a flexible task presentation system that adjusts for patient comfort, needs of the surgeon, and operating team, with multivideo recording for patients' behavior. A total of 48 patients from 3 centers underwent intraoperative language task test during awake brain surgery with the Brain MISS. Each patient was assigned 5 questions each on picture naming, reading, and listening comprehension before and during awake surgeries. The accuracy of intraoperative stimulus-response (without electrical stimulation) was recorded. The Brain MISS was to be considered effective, if the lower limit of 95% CI of patients' intraoperative response was ≥80% and also if the accuracy of intraoperative response of all patients was statistically higher than 80%.

RESULTS

All patients successfully underwent intraoperative assessment with the Brain MISS. The overall accuracy of stimulus response was 95.8% (95% CI 90.18%-100.00%), with the lower limit being higher than 80% and the response accuracy also significantly being higher than 80% in all patients (P = .006).

CONCLUSION

The Brain MISS is a portable and effective system for presenting and streamlining complicated language and cognitive tasks during awake surgery. It can also record standardized patient response data for neuroscientific research.

Hybrid Fluoroscopic and Neurophysiological Targeting of Responsive Neurostimulation of the Rolandic Cortex

BACKGROUND

Precise targeting of cortical surface electrodes to epileptogenic regions defined by anatomic and electrophysiological guideposts remains a surgical challenge during implantation of responsive neurostimulation (RNS) devices.

OBJECTIVE

To describe a hybrid fluoroscopic and neurophysiological technique for targeting of subdural cortical surface electrodes to anatomic regions with limited direct visualization, such as the interhemispheric fissure.

METHODS

Intraoperative two-dimensional (2D) fluoroscopy was used to colocalize and align an electrode for permanent device implantation with a temporary in Situ electrode placed for extraoperative seizure mapping. Intraoperative phase reversal mapping technique was performed to distinguish primary somatosensory and motor cortex.

RESULTS

We applied these techniques to optimize placement of an interhemispheric strip electrode connected to a responsive neurostimulator system for detection and treatment of seizures arising from a large perirolandic cortical malformation. Intraoperative neuromonitoring (IONM) phase reversal technique facilitated neuroanatomic mapping and electrode placement.

CONCLUSION

In challenging-to-access anatomic regions, fluoroscopy and intraoperative neurophysiology can be employed to augment targeting of neuromodulation electrodes to the site of seizure onset zone or specific neurophysiological biomarkers of clinical interest while minimizing brain retraction.

Clinical applications of neurolinguistics in neurosurgery

The protection of language function is one of the major challenges of brain surgery. Over the past century, neurosurgeons have attempted to seek the optimal strategy for the preoperative and intraoperative identification of language-related brain regions. Neurosurgeons have investigated the neural mechanism of language, developed neurolinguistics theory, and provided unique evidence to further understand the neural basis of language functions by using intraoperative cortical and subcortical electrical stimulation. With the emergence of modern neuroscience techniques and dramatic advances in language models over the last 25 years, novel language mapping methods have been applied in the neurosurgical practice to help neurosurgeons protect the brain and reduce morbidity. The rapid advancements in brain-computer interface have provided the perfect platform for the combination of neurosurgery and neurolinguistics. In this review, the history of neurolinguistics models, advancements in modern technology, role of neurosurgery in language mapping, and modern language mapping methods (including noninvasive neuroimaging techniques and invasive cortical electroencephalogram) are presented.

Two cortical representations of voice control are differentially involved in speech fluency

Recent studies have identified two distinct cortical representations of voice control in humans, the ventral and the dorsal laryngeal motor cortex. Strikingly, while persistent developmental stuttering has been linked to a white-matter deficit in the ventral laryngeal motor cortex, intensive fluency-shaping intervention modulated the functional connectivity of the dorsal laryngeal motor cortical network. Currently, it is unknown whether the underlying structural network organization of these two laryngeal representations is distinct or differently shaped by stuttering intervention. Using probabilistic diffusion tractography in 22 individuals who stutter and participated in a fluency shaping intervention, in 18 individuals who stutter and did not participate in the intervention and in 28 control participants, we here compare structural networks of the dorsal laryngeal motor cortex and the ventral laryngeal motor cortex and test intervention-related white-matter changes. We show (i) that all participants have weaker ventral laryngeal motor cortex connections compared to the dorsal laryngeal motor cortex network, regardless of speech fluency, (ii) connections of the ventral laryngeal motor cortex were stronger in fluent speakers, (iii) the connectivity profile of the ventral laryngeal motor cortex predicted stuttering severity (iv) but the ventral laryngeal motor cortex network is resistant to a fluency shaping intervention. Our findings substantiate a weaker structural organization of the ventral laryngeal motor cortical network in developmental stuttering and imply that assisted recovery supports neural compensation rather than normalization. Moreover, the resulting dissociation provides evidence for functionally segregated roles of the ventral laryngeal motor cortical and dorsal laryngeal motor cortical networks.

Evolution of Human Brain Atlases in Terms of Content, Applications, Functionality, and Availability

Human brain atlases have been evolving tremendously, propelled recently by brain big projects, and driven by sophisticated imaging techniques, advanced brain mapping methods, vast data, analytical strategies, and powerful computing. We overview here this evolution in four categories: content, applications, functionality, and availability, in contrast to other works limited mostly to content. Four atlas generations are distinguished: early cortical maps, print stereotactic atlases, early digital atlases, and advanced brain atlas platforms, and 5 avenues in electronic atlases spanning the last two generations. Content-wise, new electronic atlases are categorized into eight groups considering their scope, parcellation, modality, plurality, scale, ethnicity, abnormality, and a mixture of them. Atlas content developments in these groups are heading in 23 various directions. Application-wise, we overview atlases in neuroeducation, research, and clinics, including stereotactic and functional neurosurgery, neuroradiology, neurology, and stroke. Functionality-wise, tools and functionalities are addressed for atlas creation, navigation, individualization, enabling operations, and application-specific. Availability is discussed in media and platforms, ranging from mobile solutions to leading-edge supercomputers, with three accessibility levels. The major application-wise shift has been from research to clinical practice, particularly in stereotactic and functional neurosurgery, although clinical applications are still lagging behind the atlas content progress. Atlas functionality also has been relatively neglected until recently, as the management of brain data explosion requires powerful tools. We suggest that the future human brain atlas-related research and development activities shall be founded on and benefit from a standard framework containing the core virtual brain model cum the brain atlas platform general architecture.

Mapping Human Laryngeal Motor Cortex during Vocalization

The representations of the articulators involved in human speech production are organized somatotopically in primary motor cortex. The neural representation of the larynx, however, remains debated. Both a dorsal and a ventral larynx representation have been previously described. It is unknown, however, whether both representations are located in primary motor cortex. Here, we mapped the motor representations of the human larynx using functional magnetic resonance imaging and characterized the cortical microstructure underlying the activated regions. We isolated brain activity related to laryngeal activity during vocalization while controlling for breathing. We also mapped the articulators (the lips and tongue) and the hand area. We found two separate activations during vocalization-a dorsal and a ventral larynx representation. Structural and quantitative neuroimaging revealed that myelin content and cortical thickness underlying the dorsal, but not the ventral larynx representation, are similar to those of other primary motor representations. This finding confirms that the dorsal larynx representation is located in primary motor cortex and that the ventral one is not. We further speculate that the location of the ventral larynx representation is in premotor cortex, as seen in other primates. It remains unclear, however, whether and how these two representations differentially contribute to laryngeal motor control.

Evolution of the speech-ready brain: The voice/jaw connection in the human motor cortex

A prominent model of the origins of speech, known as the "frame/content" theory, posits that oscillatory lowering and raising of the jaw provided an evolutionary scaffold for the development of syllable structure in speech. Because such oscillations are nonvocal in most nonhuman primates, the evolution of speech required the addition of vocalization onto this scaffold in order to turn such jaw oscillations into vocalized syllables. In the present functional MRI study, we demonstrate overlapping somatotopic representations between the larynx and the jaw muscles in the human primary motor cortex. This proximity between the larynx and jaw in the brain might support the coupling between vocalization and jaw oscillations to generate syllable structure. This model suggests that humans inherited voluntary control of jaw oscillations from ancestral species, but added voluntary control of vocalization onto this via the evolution of a new brain area that came to be situated near the jaw region in the human motor cortex.

Brain Cortex Activity in Children With Anterior Open Bite: A Pilot Study

Anterior open bite (AOB) is related to functional alterations of the stomatognathic system. There are no studies concerning brain activation of the cortex comparing children with and without AOB during rest and activities such as deglutition and phonation. The aim of this study was to determine the activity of the brain cortex of children with AOB at rest and during phonation and deglutition and to evaluate the association of intelligence quotient (IQ), attention (Test of Variables of Attention, known as TOVA), beats per minute (BPM), and oxygen saturation measurement (SpO₂) with brain activity in subjects with AOB. Fourteen children (seven with AOB and seven without AOB) with mixed dentition, aged 10–13 years, underwent an IQ test, TOVA, SpO₂, and quantitative electroencephalography (QEEG). Electrodes were set in the scalp, according to the 10–20 protocol. Data were analyzed using statistical tests to assess comparisons between children with and without AOB. The results showed that IQ, TOVA, SpO₂, or BPM did not show any statistically significant differences between the groups, except for the response time (contained in TOVA) (p = 0.03). Significant differences were found for the brain activity during rest (Condition 1) of the tongue, between children with and without AOB (p < 0.05 for alpha/theta and alpha peaks), whereas there were no differences during function (Condition 2). The findings of this investigation provide insights about the cortex activity of the brain while the tongue is in the resting position in children with AOB. This may imply an altered activity of the brain cortex, which should be considered when diagnosing and treating AOB. Other diagnostic techniques derived from investigations based on neuroscience could develop new diagnostic and therapeutic techniques to give better solutions to children with malocclusions. Treatments should be focused not only on the teeth but also on the brain cortex.

The neurobiology of innate, volitional and learned vocalizations in mammals and birds

Vocalization is an ancient vertebrate trait essential to many forms of communication, ranging from courtship calls to free verse. Vocalizations may be entirely innate and evoked by sexual cues or emotional state, as with many types of calls made in primates, rodents and birds; volitional, as with innate calls that, following extensive training, can be evoked by arbitrary sensory cues in non-human primates and corvid songbirds; or learned, acoustically flexible and complex, as with human speech and the courtship songs of oscine songbirds. This review compares and contrasts the neural mechanisms underlying innate, volitional and learned vocalizations, with an emphasis on functional studies in primates, rodents and songbirds. This comparison reveals both highly conserved and convergent mechanisms of vocal production in these different groups, despite their often vast phylogenetic separation. This similarity of central mechanisms for different forms of vocal production presents experimentalists with useful avenues for gaining detailed mechanistic insight into how vocalizations are employed for social and sexual signalling, and how they can be modified through experience to yield new vocal repertoires customized to the individual's social group. This article is part of the theme issue 'What can animal communication teach us about human language?'

Neural ensemble dynamics in dorsal motor cortex during speech in people with paralysis

Speaking is a sensorimotor behavior whose neural basis is difficult to study with single neuron resolution due to the scarcity of human intracortical measurements. We used electrode arrays to record from the motor cortex 'hand knob' in two people with tetraplegia, an area not previously implicated in speech. Neurons modulated during speaking and during non-speaking movements of the tongue, lips, and jaw. This challenges whether the conventional model of a 'motor homunculus' division by major body regions extends to the single-neuron scale. Spoken words and syllables could be decoded from single trials, demonstrating the potential of intracortical recordings for brain-computer interfaces to restore speech. Two neural population dynamics features previously reported for arm movements were also present during speaking: a component that was mostly invariant across initiating different words, followed by rotatory dynamics during speaking. This suggests that common neural dynamical motifs may underlie movement of arm and speech articulators.

Decoding Speech from Intracortical Multielectrode Arrays in Dorsal "Arm/Hand Areas" of Human Motor Cortex

Neural prostheses are being developed to restore speech to people with neurological injury or disease. A key design consideration is where and how to access neural correlates of intended speech. Most prior work has examined cortical field potentials at a coarse resolution using electroencephalography (EEG) or medium resolution using electrocorticography (ECoG). The few studies of speech with single-neuron resolution recorded from ventral areas known to be part of the speech network. Here, we recorded from two 96- electrode arrays chronically implanted into the 'hand knob' area of motor cortex while a person with tetraplegia spoke. Despite being located in an area previously demonstrated to modulate during attempted arm movements, many electrodes' neuronal firing rates responded to speech production. In offline analyses, we could classify which of 9 phonemes (plus silence) was spoken with 81% single-trial accuracy using a combination of spike rate and local field potential (LFP) power. This suggests that high-fidelity speech prostheses may be possible using large-scale intracortical recordings in motor cortical areas involved in controlling speech articulators.

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

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

Subthalamic Nucleus and Sensorimotor Cortex Activity During Speech Production

The sensorimotor cortex is somatotopically organized to represent the vocal tract articulators such as lips, tongue, larynx, and jaw. How speech and articulatory features are encoded at the subcortical level, however, remains largely unknown. We analyzed LFP recordings from the subthalamic nucleus (STN) and simultaneous electrocorticography recordings from the sensorimotor cortex of 11 human subjects (1 female) with Parkinson's disease during implantation of deep-brain stimulation (DBS) electrodes while they read aloud three-phoneme words. The initial phonemes involved either articulation primarily with the tongue (coronal consonants) or the lips (labial consonants). We observed significant increases in high-gamma (60-150 Hz) power in both the STN and the sensorimotor cortex that began before speech onset and persisted for the duration of speech articulation. As expected from previous reports, in the sensorimotor cortex, the primary articulators involved in the production of the initial consonants were topographically represented by high-gamma activity. We found that STN high-gamma activity also demonstrated specificity for the primary articulator, although no clear topography was observed. In general, subthalamic high-gamma activity varied along the ventral-dorsal trajectory of the electrodes, with greater high-gamma power recorded in the dorsal locations of the STN. Interestingly, the majority of significant articulator-discriminative activity in the STN occurred before that in sensorimotor cortex. These results demonstrate that articulator-specific speech information is contained within high-gamma activity of the STN, but with different spatial and temporal organization compared with similar information encoded in the sensorimotor cortex.SIGNIFICANCE STATEMENT Clinical and electrophysiological evidence suggest that the subthalamic nucleus (STN) is involved in speech; however, this important basal ganglia node is ignored in current models of speech production. We previously showed that STN neurons differentially encode early and late aspects of speech production, but no previous studies have examined subthalamic functional organization for speech articulators. Using simultaneous LFP recordings from the sensorimotor cortex and the STN in patients with Parkinson's disease undergoing deep-brain stimulation surgery, we discovered that STN high-gamma activity tracks speech production at the level of vocal tract articulators before the onset of vocalization and often before related cortical encoding.

Inhibition of Manual Movements at Speech Arrest Sites in the Posterior Inferior Frontal Lobe

BACKGROUND

Intraoperative stimulation of the posterior inferior frontal lobe (IFL) induces speech arrest, which is often interpreted as demonstration of essential language function. However, prior reports have described “negative motor areas” in the IFL, sites where stimulation halts ongoing limb motor activity.

OBJECTIVE

To investigate the spatial and functional relationship between IFL speech arrest areas and negative motor areas (NMAs).

METHODS

In this retrospective cohort study, intraoperative stimulation mapping was performed to localize speech and motor function, as well as arrest of hand movement, hand posture, and guitar playing in a set of patients undergoing awake craniotomy for dominant hemisphere pathologies. The incidence and localization of speech arrest and motor inhibition was analyzed.

RESULTS

Eleven patients underwent intraoperative localization of speech arrest sites and inhibitory motor areas. A total of 17 speech arrest sites were identified in the dominant frontal lobe, and, of these, 5 sites (29.4%) were also identified as NMAs. Speech arrest and arrest of guitar playing was also evoked by a single IFL site in 1 subject.

CONCLUSION

Inferior frontal gyrus speech arrest sites do not function solely in speech production. These findings provide further evidence for the complexity of language organization, and suggest the need for refined mapping strategies that discern between language-specific sites and inhibitory motor areas.

How does human motor cortex regulate vocal pitch in singers?

Vocal pitch is used as an important communicative device by humans, as found in the melodic dimension of both speech and song. Vocal pitch is determined by the degree of tension in the vocal folds of the larynx, which itself is influenced by complex and nonlinear interactions among the laryngeal muscles. The relationship between these muscles and vocal pitch has been described by a mathematical model in the form of a set of 'control rules'. We searched for the biological implementation of these control rules in the larynx motor cortex of the human brain. We scanned choral singers with functional magnetic resonance imaging as they produced discrete pitches at four different levels across their vocal range. While the locations of the larynx motor activations varied across singers, the activation peaks for the four pitch levels were highly consistent within each individual singer. This result was corroborated using multi-voxel pattern analysis, which demonstrated an absence of patterned activations differentiating any pairing of pitch levels. The complex and nonlinear relationships between the multiple laryngeal muscles that control vocal pitch may obscure the neural encoding of vocal pitch in the brain.

The Control of Vocal Pitch in Human Laryngeal Motor Cortex

In speech, the highly flexible modulation of vocal pitch creates intonation patterns that speakers use to convey linguistic meaning. This human ability is unique among primates. Here, we used high-density cortical recordings directly from the human brain to determine the encoding of vocal pitch during natural speech. We found neural populations in bilateral dorsal laryngeal motor cortex (dLMC) that selectively encoded produced pitch but not non-laryngeal articulatory movements. This neural population controlled short pitch accents to express prosodic emphasis on a word in a sentence. Other larynx cortical representations controlling voicing and longer pitch phrase contours were found at separate sites. dLMC sites also encoded vocal pitch during a non-speech singing task. Finally, direct focal stimulation of dLMC evoked laryngeal movements and involuntary vocalization, confirming its causal role in feedforward control. Together, these results reveal the neural basis for the voluntary control of vocal pitch in human speech. VIDEO ABSTRACT.

Encoding of Articulatory Kinematic Trajectories in Human Speech Sensorimotor Cortex

When speaking, we dynamically coordinate movements of our jaw, tongue, lips, and larynx. To investigate the neural mechanisms underlying articulation, we used direct cortical recordings from human sensorimotor cortex while participants spoke natural sentences that included sounds spanning the entire English phonetic inventory. We used deep neural networks to infer speakers' articulator movements from produced speech acoustics. Individual electrodes encoded a diversity of articulatory kinematic trajectories (AKTs), each revealing coordinated articulator movements toward specific vocal tract shapes. AKTs captured a wide range of movement types, yet they could be differentiated by the place of vocal tract constriction. Additionally, AKTs manifested out-and-back trajectories with harmonic oscillator dynamics. While AKTs were functionally stereotyped across different sentences, context-dependent encoding of preceding and following movements during production of the same phoneme demonstrated the cortical representation of coarticulation. Articulatory movements encoded in sensorimotor cortex give rise to the complex kinematics underlying continuous speech production. VIDEO ABSTRACT.

Connectivity and the search for specializations in the language-capable brain

The search for the anatomical basis of language has traditionally been a search for specializations. More recently such research has focused both on aspects of brain organization that are unique to humans and aspects shared with other primates. This work has mostly concentrated on the architecture of connections between brain areas. However, as specializations can take many guises, comparison of anatomical organization across species is often complicated. We demonstrate how viewing different types of specializations within a common framework allows one to better appreciate both shared and unique aspects of brain organization. We illustrate this point by discussing recent insights into the anatomy of the dorsal language pathway to the frontal cortex and areas for laryngeal control in the motor cortex.

Direct cortical stimulation of inferior frontal cortex disrupts both speech and music production in highly trained musicians

Music and speech are human-specific behaviours that share numerous properties, including the fine motor skills required to produce them. Given these similarities, previous work has suggested that music and speech may at least partially share neural substrates. To date, much of this work has focused on perception, and has not investigated the neural basis of production, particularly in trained musicians. Here, we report two rare cases of musicians undergoing neurosurgical procedures, where it was possible to directly stimulate the left hemisphere cortex during speech and piano/guitar music production tasks. We found that stimulation to left inferior frontal cortex, including pars opercularis and ventral pre-central gyrus, caused slowing and arrest for both speech and music, and note sequence errors for music. Stimulation to posterior superior temporal cortex only caused production errors during speech. These results demonstrate partially dissociable networks underlying speech and music production, with a shared substrate in frontal regions.

Decoding Speech With Integrated Hybrid Signals Recorded From the Human Ventral Motor Cortex

Restoration of speech communication for locked-in patients by means of brain computer interfaces (BCIs) is currently an important area of active research. Among the neural signals obtained from intracranial recordings, single/multi-unit activity (SUA/MUA), local field potential (LFP), and electrocorticography (ECoG) are good candidates for an input signal for BCIs. However, the question of which signal or which combination of the three signal modalities is best suited for decoding speech production remains unverified. In order to record SUA, LFP, and ECoG simultaneously from a highly localized area of human ventral sensorimotor cortex (vSMC), we fabricated an electrode the size of which was 7 by 13 mm containing sparsely arranged microneedle and conventional macro contacts. We determined which signal modality is the most capable of decoding speech production, and tested if the combination of these signals could improve the decoding accuracy of spoken phonemes. Feature vectors were constructed from spike frequency obtained from SUAs and event-related spectral perturbation derived from ECoG and LFP signals, then input to the decoder. The results showed that the decoding accuracy for five spoken vowels was highest when features from multiple signals were combined and optimized for each subject, and reached 59% when averaged across all six subjects. This result suggests that multi-scale signals convey complementary information for speech articulation. The current study demonstrated that simultaneous recording of multi-scale neuronal activities could raise decoding accuracy even though the recording area is limited to a small portion of cortex, which is advantageous for future implementation of speech-assisting BCIs.

Poor neuro-motor tuning of the human larynx: a comparison of sung and whistled pitch imitation

Vocal imitation is a hallmark of human communication that underlies the capacity to learn to speak and sing. Even so, poor vocal imitation abilities are surprisingly common in the general population and even expert vocalists cannot match the precision of a musical instrument. Although humans have evolved a greater degree of control over the laryngeal muscles that govern voice production, this ability may be underdeveloped compared with control over the articulatory muscles, such as the tongue and lips, volitional control of which emerged earlier in primate evolution. Human participants imitated simple melodies by either singing (i.e. producing pitch with the larynx) or whistling (i.e. producing pitch with the lips and tongue). Sung notes were systematically biased towards each individual's habitual pitch, which we hypothesize may act to conserve muscular effort. Furthermore, while participants who sung more precisely also whistled more precisely, sung imitations were less precise than whistled imitations. The laryngeal muscles that control voice production are under less precise control than the oral muscles that are involved in whistling. This imprecision may be due to the relatively recent evolution of volitional laryngeal-motor control in humans, which may be tuned just well enough for the coarse modulation of vocal-pitch in speech.

Neural reuse of action perception circuits for language, concepts and communication

Neurocognitive and neurolinguistics theories make explicit statements relating specialized cognitive and linguistic processes to specific brain loci. These linking hypotheses are in need of neurobiological justification and explanation. Recent mathematical models of human language mechanisms constrained by fundamental neuroscience principles and established knowledge about comparative neuroanatomy offer explanations for where, when and how language is processed in the human brain. In these models, network structure and connectivity along with action- and perception-induced correlation of neuronal activity co-determine neurocognitive mechanisms. Language learning leads to the formation of action perception circuits (APCs) with specific distributions across cortical areas. Cognitive and linguistic processes such as speech production, comprehension, verbal working memory and prediction are modelled by activity dynamics in these APCs, and combinatorial and communicative-interactive knowledge is organized in the dynamics within, and connections between APCs. The network models and, in particular, the concept of distributionally-specific circuits, can account for some previously not well understood facts about the cortical 'hubs' for semantic processing and the motor system's role in language understanding and speech sound recognition. A review of experimental data evaluates predictions of the APC model and alternative theories, also providing detailed discussion of some seemingly contradictory findings. Throughout, recent disputes about the role of mirror neurons and grounded cognition in language and communication are assessed critically.

New Developments in Understanding the Complexity of Human Speech Production

Speech is one of the most unique features of human communication. Our ability to articulate our thoughts by means of speech production depends critically on the integrity of the motor cortex. Long thought to be a low-order brain region, exciting work in the past years is overturning this notion. Here, we highlight some of major experimental advances in speech motor control research and discuss the emerging findings about the complexity of speech motocortical organization and its large-scale networks. This review summarizes the talks presented at a symposium at the Annual Meeting of the Society of Neuroscience; it does not represent a comprehensive review of contemporary literature in the broader field of speech motor control.

A Near-Infrared Spectroscopy Study on Cortical Hemodynamic Responses to Normal and Whispered Speech in 3- to 7-Year-Old Children

PURPOSE

The purpose of this study was to assess cortical hemodynamic response patterns in 3- to 7-year-old children listening to two speech modes: normally vocalized and whispered speech. Understanding whispered speech requires processing of the relatively weak, noisy signal, as well as the cognitive ability to understand the speaker's reason for whispering.

METHOD

Near-infrared spectroscopy (NIRS) was used to assess changes in cortical oxygenated hemoglobin from 16 typically developing children.

RESULTS

A profound difference in oxygenated hemoglobin levels between the speech modes was found over left ventral sensorimotor cortex. In particular, over areas that represent speech articulatory body parts and motion, such as the larynx, lips, and jaw, oxygenated hemoglobin was higher for whisper than for normal speech. The weaker stimulus, in terms of sound energy, thus induced the more profound hemodynamic response. This, moreover, occurred over areas involved in speech articulation, even though the children did not overtly articulate speech during measurements.

CONCLUSION

Because whisper is a special form of communication not often used in daily life, we suggest that the hemodynamic response difference over left ventral sensorimotor cortex resulted from inner (covert) practice or imagination of the different articulatory actions necessary to produce whisper as opposed to normal speech.

A contemporary framework of language processing in the human brain in the context of preoperative and intraoperative language mapping

INTRODUCTION

The emergence of advanced in vivo neuroimaging methods has redefined the understanding of brain function with a shift from traditional localizationist models to more complex and widely distributed neural networks. In human language processing, the traditional localizationist models of Wernicke and Broca have fallen out of favor for a dual-stream processing system involving complex networks organized over vast areas of the dominant hemisphere. The current review explores the cortical function and white matter connections of human language processing, as well as their relevance to surgical planning.

METHODS

We performed a systematic review of the literature with narrative data analysis.

RESULTS

Although there is significant heterogeneity in the literature over the past century of exploration, modern evidence provides new insight into the true cortical function and white matter anatomy of human language. Intraoperative data and postoperative outcome studies confirm a widely distributed language network extending far beyond the traditional cortical areas of Wernicke and Broca.

CONCLUSIONS

The anatomic distribution of language networks, based on current theories, is explored to present a modern and clinically relevant interpretation of language function. Within this framework, we present current knowledge regarding the known effects of damage to both cortical and subcortical components of these language networks. Ideally, we hope this framework will provide a common language for which to base future clinical studies in human language function.