Cognitive control of vocalizations in the primate ventrolateral-dorsomedial frontal (VLF-DMF) brain network

Volitional inspiration is mediated by two independent output channels in the primary motor cortex

The diaphragm is a multifunctional muscle that mediates both autonomic and volitional inspiration. It is critically involved in vocalization, postural stability, and expulsive core-trunk functions, such as coughing, hiccups, and vomiting. In macaque monkeys, we used retrograde transneuronal transport of rabies virus injected into the left hemidiaphragm to identify cortical neurons that have multisynaptic connections with phrenic motoneurons. Our research demonstrates that representation of the diaphragm in the primary motor cortex (M1) is split into two spatially separate and independent sites. No cortico-cortical connections are known to exist between these two sites. One site is located dorsal to the arm representation within the central sulcus and the second site is lateral to the arm. The dual representation of the diaphragm warrants a revision to the somatotopic map of M1. The dorsal diaphragm representation overlaps with trunk and axial musculature. It is ideally situated to coordinate with these muscles during volitional inspiration and in producing intra-abdominal pressure gradients. The lateral site overlaps the origin of M1 projections to a laryngeal muscle, the cricothyroid. This observation suggests that the coordinated control of laryngeal muscles and the diaphragm during vocalization may be achieved, in part, by co-localization of their representations in M1. The neural organization of the two diaphragm sites underlies a new perspective for interpreting functional imaging studies of respiration and/or vocalization. Furthermore, our results provide novel evidence supporting the concept that overlapping output channels within M1 are a prerequisite for the formation of muscle synergies underlying fine motor control.

Anatomo-functional correspondence in the voice-selective regions of human prefrontal cortex

Group level analyses of functional regions involved in voice perception show evidence of 3 sets of bilateral voice-sensitive activations in the human prefrontal cortex, named the anterior, middle and posterior Frontal Voice Areas (FVAs). However, the relationship with the underlying sulcal anatomy, highly variable in this region, is still unknown. We examined the inter-individual variability of the FVAs in conjunction with the sulcal anatomy. To do so, anatomical and functional MRI scans from 74 subjects were analyzed to generate individual contrast maps of the FVAs and relate them to each subject's manually labeled prefrontal sulci. We report two major results. First, the frontal activations for the voice are significantly associated with the sulcal anatomy. Second, this correspondence with the sulcal anatomy at the individual level is a better predictor than coordinates in the MNI space. These findings offer new perspectives for the understanding of anatomical-functional correspondences in this complex cortical region. They also shed light on the importance of considering individual-specific variations in subject's anatomy.

The relevance of the unique anatomy of the human prefrontal operculum to the emergence of speech

Identifying the evolutionary origins of human speech remains a topic of intense scientific interest. Here we describe a unique feature of adult human neuroanatomy compared to chimpanzees and other primates that may provide an explanation of changes that occurred to enable the capacity for speech. That feature is the Prefrontal extent of the Frontal Operculum (PFOp) region, which is located in the ventrolateral prefrontal cortex, adjacent and ventromedial to the classical Broca's area. We also show that, in chimpanzees, individuals with the most human-like PFOp, particularly in the left hemisphere, have greater oro-facial and vocal motor control abilities. This critical discovery, when combined with recent paleontological evidence, suggests that the PFOp is a recently evolved feature of human cortical structure (perhaps limited to the genus Homo) that emerged in response to increasing selection for cognitive and motor functions evident in modern speech abilities.

A vocalization-processing network in marmosets

Vocalizations play an important role in the daily life of primates and likely form the basis of human language. Functional imaging studies have demonstrated that listening to voices activates a fronto-temporal voice perception network in human participants. Here, we acquired whole-brain ultrahigh-field (9.4 T) fMRI in awake marmosets (Callithrix jacchus) and demonstrate that these small, highly vocal New World primates possess a similar fronto-temporal network, including subcortical regions, that is activated by the presentation of conspecific vocalizations. The findings suggest that the human voice perception network has evolved from an ancestral vocalization-processing network that predates the separation of New and Old World primates.

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.

Background noise responding neurons in the inferior colliculus of the CF-FM bat, Hipposideros pratti

The Lombard effect, referring to an involuntary rise in vocal intensity, is a widespread vertebrate mechanism that aims to maintain signal efficiency in response to ambient noise. Previous studies showed that the Lombard effect could be sufficiently implemented at subcortical levels and operated by continuously monitoring background noise, requiring some subcortical auditory sensitive neurons to have continuous responses to background noise. However, such neurons have not been well characterized. The inferior colliculus (IC) is a major auditory integration center under the auditory cortex and provides projections to the putative vocal pattern generator in the brainstem. Thus, it is reasonable to speculate that the IC is a likely auditory nucleus candidate having background noise responding neurons (BNR neurons). In the present study, we isolated 183 sound-sensitive IC neurons in a constant frequency-frequency modulation bat, Hipposideros pratti, and found that around 19% of these IC neurons are BNR neurons when stimulated with 70 dB SPL background white noise. Their firing rates in response to noise increased with increasing noise intensity and could be suppressed by sound stimulation. Furthermore, compared to neurons with similar best frequencies, the BNR neurons had smaller Q_10-dB values and lower noise-induced minimal threshold change, indicating that BNR neurons received fewer inhibitory inputs. These results suggested that the BNR neurons are ideal candidates for collecting information about background noise. We proposed that the BNR neurons synapsed with neurons in vocal-pattern-generating networks in the brainstem and initiated the Lombard effect by a feed-forward loop.

Auditory verbal hallucination can be evoked by prefrontal epileptic seizure

Auditory verbal hallucinations (AVHs) have been reported in neocortical temporal epileptic seizures and have been considered highly associated with implication of auditory cortex by epileptic discharges or electrical stimulation. Herein, we report two rare frontal epilepsy cases in which AVHs featured the habitual seizures. The epileptogenic zones of these two patients were localized in the dorsal and orbitomedial prefrontal cortex, respectively by stereoelectroencephalography (SEEG) monitoring. Comparing with the AVHs in schizophrenia, we postulated that the phenomenological similarities between the two sets of AVHs imply homology in mechanisms. Ictal SEEG confirmed that the wide involvement of prefrontal-cingulate-auditory cortical network by low-voltage fast activity corresponded the occurrence with AVHs during frontal epileptic seizures. Electrical stimulation study of one of the two cases highlighted the causal role of prefrontal-cingulate cortex in the emergence of AVHs. Based on our clinical observation, SEEG findings, and electrical cortical stimulation, we supposed that wide implication of prefrontal-cingulate-auditory cortical network during epileptic seizure underlie the emergence of AVHs, and further hypothesized that AVHs could be yielded by transient deficit of self-monitoring for inner speech in focal epileptic seizures.

Cognitive control of song production by humpback whales

Singing humpback whales are highly versatile vocalizers, producing complex sequences of sounds that they vary throughout adulthood. Past analyses of humpback whale song have emphasized yearly variations in structural features of songs made collectively by singers within a population with comparatively little attention given to the ways that individual singers vary consecutive songs. As a result, many researchers describe singing by humpback whales as a process in which singers produce sequences of repeating sound patterns. Here, we show that such characterizations misrepresent the degree to which humpback whales flexibly and dynamically control the production of sounds and sound patterns within song sessions. Singers recorded off the coast of Hawaii continuously morphed units along multiple acoustic dimensions, with the degree and direction of morphing varying across parallel streams of successive units. Individual singers also produced multiple phrase variants (structurally similar, but acoustically distinctive sequences) within song sessions. The precision with which individual singers maintained some acoustic properties of phrases and morphing trajectories while flexibly changing others suggests that singing humpback whales actively select and adjust acoustic elements of their songs in real time rather than simply repeating stereotyped sound patterns within song sessions.

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.

Structural Brain Asymmetries for Language: A Comparative Approach across Primates

Humans are the only species that can speak. Nonhuman primates, however, share some ‘domain-general’ cognitive properties that are essential to language processes. Whether these shared cognitive properties between humans and nonhuman primates are the results of a continuous evolution [homologies] or of a convergent evolution [analogies] remain difficult to demonstrate. However, comparing their respective underlying structure—the brain—to determinate their similarity or their divergence across species is critical to help increase the probability of either of the two hypotheses, respectively. Key areas associated with language processes are the Planum Temporale, Broca’s Area, the Arcuate Fasciculus, Cingulate Sulcus, The Insula, Superior Temporal Sulcus, the Inferior Parietal lobe, and the Central Sulcus. These structures share a fundamental feature: They are functionally and structurally specialised to one hemisphere. Interestingly, several nonhuman primate species, such as chimpanzees and baboons, show human-like structural brain asymmetries for areas homologous to key language regions. The question then arises: for what function did these asymmetries arise in non-linguistic primates, if not for language per se? In an attempt to provide some answers, we review the literature on the lateralisation of the gestural communication system, which may represent the missing behavioural link to brain asymmetries for language area’s homologues in our common ancestor.

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.

Chronic recording of cortical activity underlying vocalization in awake minipigs

BACKGROUND

Investigating brain dynamics underlying vocal production in animals is a powerful way to inform on the neural bases of human speech. In particular, brain networks underlying vocal production in non-human primates show striking similarities with the human speech production network. However, despite increasing findings also in birds and more recently in rodents, the extent to which the primate vocal cortical network model generalizes to other non-primate mammals remains unclear. Especially, no domestic species has yet been proposed to investigate vocal brain activity using electrophysiological approaches.

NEW METHOD

In the present study, we introduce a novel experimental paradigm to identify the cortical dynamics underlying vocal production in behaving minipigs. A key problem to chronically implant cortical probes in pigs is the presence and growth of frontal sinuses extending caudally to the parietal bone and preventing safe access to neural structures with conventional craniotomy in adult animals.

RESULTS

Here we first show that implantations of soft ECoG grids can be done safely using conventional craniotomy in minipigs younger than 5 months, a period when sinuses are not yet well developed. Using wireless recordings in behaving animals, we further show activation of the motor and premotor cortex around the onset of vocal production of grunts, the most common vocalization of pigs.

CONCLUSION

These results suggest that minipigs, which are very loquacious and social animals, can be a good experimental large animal model to study the cortical bases of vocal production.

The Arcuate Fasciculus and language origins: Disentangling existing conceptions that influence evolutionary accounts

The Arcuate Fasciculus (AF) is of considerable interdisciplinary interest, because of its major implication in language processing. Theories about language brain evolution are based on anatomical differences in the AF across primates. However, changing methodologies and nomenclatures have resulted in conflicting findings regarding interspecies AF differences: Historical knowledge about the AF originated from human blunt dissections and later from monkey tract-tracing studies. Contemporary tractography studies reinvestigate the fasciculus' morphology, but remain heavily bound to unclear anatomical priors and methodological limitations. First, we aim to disentangle the influences of these three epistemological steps on existing AF conceptions, and to propose a contemporary model to guide future work. Second, considering the influence of various AF conceptions, we discuss four key evolutionary changes that propagated current views about language evolution: 1) frontal terminations, 2) temporal terminations, 3) greater Dorsal- versus Ventral Pathway expansion, 4) lateralisation. We conclude that new data point towards a more shared AF anatomy across primates than previously described. Language evolution theories should incorporate this continuous AF evolution across primates.

Functional and molecular characterization of a non-human primate model of autism spectrum disorder shows similarity with the human disease

Autism spectrum disorder (ASD) is a multifactorial disorder with characteristic synaptic and gene expression changes. Early intervention during childhood is thought to benefit prognosis. Here, we examined the changes in cortical synaptogenesis, synaptic function, and gene expression from birth to the juvenile stage in a marmoset model of ASD induced by valproic acid (VPA) treatment. Early postnatally, synaptogenesis was reduced in this model, while juvenile-age VPA-treated marmosets showed increased synaptogenesis, similar to observations in human tissue. During infancy, synaptic plasticity transiently increased and was associated with altered vocalization. Synaptogenesis-related genes were downregulated early postnatally. At three months of age, the differentially expressed genes were associated with circuit remodeling, similar to the expression changes observed in humans. In summary, we provide a functional and molecular characterization of a non-human primate model of ASD, highlighting its similarity to features observed in human ASD.

Sulcal Morphology in Cingulate Cortex is Associated with Voluntary Oro-Facial Motor Control and Gestural Communication in Chimpanzees (Pan troglodytes)

Individual differences in sulcal variation within the anterior and mid-cingulate cortex of the human brain, particularly the presence or absence of a paracingulate sulcus (PCGS), are associated with various motor and cognitive processes. Recently, it has been reported that chimpanzees possess a PCGS, previously thought to be a unique feature of the human brain. Here, we examined whether individual variation in the presence or absence of a PCGS as well as the variability in the intralimbic sulcus (ILS) are associated with oro-facial motor control, handedness for manual gestures, and sex in a sample of MRI scans obtained in 225 chimpanzees. Additionally, we quantified the depth of the cingulate sulcus (CGS) along the anterior-posterior axis and tested for association with oro-facial motor control, handedness, and sex. Chimpanzees with better oro-facial motor control were more likely to have a PCGS, particularly in the left hemisphere compared to those with poorer control. Male chimpanzees with better oro-facial motor control showed increased leftward asymmetries in the depth of the anterior CGS, whereas female chimpanzees showed the opposite pattern. Significantly, more chimpanzees had an ILS in the left compared to the right hemisphere, but variability in this fold was not associated with sex, handedness, or oro-facial motor control. Finally, significant population-level leftward asymmetries were found in the anterior portion of the CGS, whereas significant rightward biases were evident in the posterior regions. The collective results suggest that the emergence of a PCGS and enhanced gyrification within the anterior and mid-cingulate gyrus may have directly or indirectly evolved in response to selection for increasing oro-facial motor control in primates.

The evolution of hierarchical structure building capacity for language and music: a bottom-up perspective

A central property of human language is its hierarchical structure. Humans can flexibly combine elements to build a hierarchical structure expressing rich semantics. A hierarchical structure is also considered as playing a key role in many other human cognitive domains. In music, auditory-motor events are combined into hierarchical pitch and/or rhythm structure expressing affect. How did such a hierarchical structure building capacity evolve? This paper investigates this question from a bottom-up perspective based on a set of action-related components as a shared basis underlying cognitive capacities of nonhuman primates and humans. Especially, I argue that the evolution of hierarchical structure building capacity for language and music is tractable for comparative evolutionary study once we focus on the gradual elaboration of shared brain architecture: the cortico-basal ganglia-thalamocortical circuits for hierarchical control of goal-directed action and the dorsal pathways for hierarchical internal models. I suggest that this gradual elaboration of the action-related brain architecture in the context of vocal control and tool-making went hand in hand with amplification of working memory, and made the brain ready for hierarchical structure building in language and music.

Corticostriatal Projections of Macaque Area 44

Ventrolateral frontal area 44 is implicated in inhibitory motor functions and facilitating prefrontal control over vocalization. The contribution of corticostriatal circuits to area 44 functions is unclear, as prior investigation of area 44 projections to the striatum—a central structure in motor circuits—is limited. Here, we used anterograde and retrograde tracing in macaques to map the innervation zone of area 44 corticostriatal projections, quantify their strengths, and evaluate their convergence with corticostriatal projections from other frontal cortical regions. First, whereas terminal fields from a rostral area 44 injection site were found primarily in the central caudate nucleus, those from a caudal area 44 injection site were found primarily in the ventrolateral putamen. Second, amongst sampled injection sites, area 44 input as a percentage of total frontal cortical input was highest in the ventral putamen at the level of the anterior commissure. Third, area 44 projections converged with orofacial premotor area 6VR and other motor-related projections (in the putamen), and with nonmotor prefrontal projections (in the caudate nucleus). Findings support the role of area 44 as an interface between motor and nonmotor functional domains, possibly facilitated by rostral and caudal area 44 subregions with distinct corticostriatal connectivity profiles.

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.

Theta Synchronization of Phonatory and Articulatory Systems in Marmoset Monkey Vocal Production

Human speech shares a 3-8-Hz theta rhythm across all languages [1-3]. According to the frame/content theory of speech evolution, this rhythm corresponds to syllabic rates derived from natural mandibular-associated oscillations [4]. The underlying pattern originates from oscillatory movements of articulatory muscles [4, 5] tightly linked to periodic vocal fold vibrations [4, 6, 7]. Such phono-articulatory rhythms have been proposed as one of the crucial preadaptations for human speech evolution [3, 8, 9]. However, the evolutionary link in phono-articulatory rhythmicity between vertebrate vocalization and human speech remains unclear. From the phonatory perspective, theta oscillations might be phylogenetically preserved throughout all vertebrate clades [10-12]. From the articulatory perspective, theta oscillations are present in non-vocal lip smacking [1, 13, 14], teeth chattering [15], vocal lip smacking [16], and clicks and faux-speech [17] in non-human primates, potential evolutionary precursors for speech rhythmicity [1, 13]. Notably, a universal phono-articulatory rhythmicity similar to that in human speech is considered to be absent in non-human primate vocalizations, typically produced with sound modulations lacking concomitant articulatory movements [1, 9, 18]. Here, we challenge this view by investigating the coupling of phonatory and articulatory systems in marmoset vocalizations. Using quantitative measures of acoustic call structure, e.g., amplitude envelope, and call-associated articulatory movements, i.e., inter-lip distance, we show that marmosets display speech-like bi-motor rhythmicity. These oscillations are synchronized and phase locked at theta rhythms. Our findings suggest that oscillatory rhythms underlying speech production evolved early in the primate lineage, identifying marmosets as a suitable animal model to decipher the evolutionary and neural basis of coupled phono-articulatory movements.

The Evolution of Human Vocal Emotion

Vocal affect is a subcomponent of emotion programs that coordinate a variety of physiological and psychological systems. Emotional vocalizations comprise a suite of vocal behaviors shaped by evolution to solve adaptive social communication problems. The acoustic forms of vocal emotions are often explicable with reference to the communicative functions they serve. An adaptationist approach to vocal emotions requires that we distinguish between evolved signals and byproduct cues, and understand vocal affect as a collection of multiple strategic communicative systems subject to the evolutionary dynamics described by signaling theory. We should expect variability across disparate societies in vocal emotion according to culturally evolved pragmatic rules, and universals in vocal production and perception to the extent that form–function relationships are present.

Cognitive control of orofacial motor and vocal responses in the ventrolateral and dorsomedial human frontal cortex

In the primate brain, a set of areas in the ventrolateral frontal (VLF) cortex and the dorsomedial frontal (DMF) cortex appear to control vocalizations. The basic role of this network in the human brain and how it may have evolved to enable complex speech remain unknown. In the present functional neuroimaging study of the human brain, a multidomain protocol was utilized to investigate the roles of the various areas that comprise the VLF-DMF network in learning rule-based cognitive selections between different types of motor actions: manual, orofacial, nonspeech vocal, and speech vocal actions. Ventrolateral area 44 (a key component of the Broca's language production region in the human brain) is involved in the cognitive selection of orofacial, as well as, speech and nonspeech vocal responses; and the midcingulate cortex is involved in the analysis of speech and nonspeech vocal feedback driving adaptation of these responses. By contrast, the cognitive selection of speech vocal information requires this former network and the additional recruitment of area 45 and the presupplementary motor area. We propose that the basic function expressed by the VLF-DMF network is to exert cognitive control of orofacial and vocal acts and, in the language dominant hemisphere of the human brain, has been adapted to serve higher speech function. These results pave the way to understand the potential changes that could have occurred in this network across primate evolution to enable speech production.

Cognitive control of complex motor behavior in marmoset monkeys

Marmosets have attracted significant interest in the life sciences. Similarities with human brain anatomy and physiology, such as the granular frontal cortex, as well as the development of transgenic lines and potential for transferring rodent neuroscientific techniques to small primates make them a promising neurodegenerative and neuropsychiatric model system. However, whether marmosets can exhibit complex motor tasks in highly controlled experimental designs—one of the prerequisites for investigating higher-order control mechanisms underlying cognitive motor behavior—has not been demonstrated. We show that marmosets can be trained to perform vocal behavior in response to arbitrary visual cues in controlled operant conditioning tasks. Our results emphasize the marmoset as a suitable model to study complex motor behavior and the evolution of cognitive control underlying speech.

Whether marmosets can exhibit complex motor tasks in controlled experimental designs has not yet been demonstrated. Here, the authors show that marmoset monkeys can be trained to call on command in controlled operant conditioning tasks.

Multimodal communication and language origins: integrating gestures and vocalizations

The presence of divergent and independent research traditions in the gestural and vocal domains of primate communication has resulted in major discrepancies in the definition and operationalization of cognitive concepts. However, in recent years, accumulating evidence from behavioural and neurobiological research has shown that both human and non-human primate communication is inherently multimodal. It is therefore timely to integrate the study of gestural and vocal communication. Herein, we review evidence demonstrating that there is no clear difference between primate gestures and vocalizations in the extent to which they show evidence for the presence of key language properties: intentionality, reference, iconicity and turn-taking. We also find high overlap in the neurobiological mechanisms producing primate gestures and vocalizations, as well as in ontogenetic flexibility. These findings confirm that human language had multimodal origins. Nonetheless, we note that in great apes, gestures seem to fulfil a carrying (i.e. predominantly informative) role in close-range communication, whereas the opposite holds for face-to-face interactions of humans. This suggests an evolutionary shift in the carrying role from the gestural to the vocal stream, and we explore this transition in the carrying modality. Finally, we suggest that future studies should focus on the links between complex communication, sociality and cooperative tendency to strengthen the study of language origins.

Language Origins Viewed in Spontaneous and Interactive Vocal Rates of Human and Bonobo Infants

From the first months of life, human infants produce "protophones," speech-like, non-cry sounds, presumed absent, or only minimally present in other apes. But there have been no direct quantitative comparisons to support this presumption. In addition, by 2 months, human infants show sustained face-to-face interaction using protophones, a pattern thought also absent or very limited in other apes, but again, without quantitative comparison. Such comparison should provide evidence relevant to determining foundations of language, since substantially flexible vocalization, the inclination to explore vocalization, and the ability to interact socially by means of vocalization are foundations for language. Here we quantitatively compare data on vocalization rates in three captive bonobo (Pan paniscus) mother-infant pairs with various sources of data from our laboratories on human infant vocalization. Both humans and bonobos produced distress sounds (cries/screams) and laughter. The bonobo infants also produced sounds that were neither screams nor laughs and that showed acoustic similarities to the human protophones. These protophone-like sounds confirm that bonobo infants share with humans the capacity to produce vocalizations that appear foundational for language. Still, there were dramatic differences between the species in both quantity and function of the protophone and protophone-like sounds. The bonobo protophone-like sounds were far less frequent than the human protophones, and the human protophones were far less likely to be interpreted as complaints and more likely as vocal play. Moreover, we found extensive vocal interaction between human infants and mothers, but no vocal interaction in the bonobo mother-infant pairs-while bonobo mothers were physically responsive to their infants, we observed no case of a bonobo mother vocalization directed to her infant. Our cross-species comparison focuses on low- and moderate-arousal circumstances because we reason the roots of language entail vocalization not triggered by excitement, for example, during fighting or intense play. Language appears to be founded in flexible vocalization, used to regulate comfortable social interaction, to share variable affective states at various levels of arousal, and to explore vocalization itself.

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.

Critical role of the right VLPFC in emotional regulation of social exclusion: a tDCS study

There is abundant evidence suggesting that the right ventrolateral prefrontal cortex (rVLPFC) plays an important role in down-regulating the emotional response to social exclusion. However, a causal relationship between rVLPFC function and explicit emotional regulation is not clear in the context of social exclusion. This study employed anodal transcranial direct current stimulation (tDCS) to activate rVLPFC while participants used emotional regulation to reappraise pictures of social exclusion. Forty-four participants were randomly assigned to an active tDCS group or a sham group. Both groups viewed social exclusion images under two conditions: in the no-reappraisal condition, participants were instructed to passively view social exclusion images; in the reappraisal condition, they reappraised the images to down-regulate negative emotional responses. Compared to sham stimulation, anodal tDCS over the rVLPFC resulted in less negative emotion ratings, and produced significantly smaller pupil diameter in the reappraisal, compared to no-reappraisal block. The tDCS also led to longer fixation durations to rejectees and shorter fixation durations to rejecters. Taken together, these findings suggest a causal role for rVLPFC in down-regulation of negative emotions produced by social exclusion. This study has implications for clinical interventions targeting emotional regulation deficits.

Mapping the distribution of language related genes FoxP1, FoxP2, and CntnaP2 in the brains of vocal learning bat species

Genes including FOXP2, FOXP1, and CNTNAP2, have been implicated in human speech and language phenotypes, pointing to a role in the development of normal language‐related circuitry in the brain. Although speech and language are unique to humans a comparative approach is possible by addressing language‐relevant traits in animal systems. One such trait, vocal learning, represents an essential component of human spoken language, and is shared by cetaceans, pinnipeds, elephants, some birds and bats. Given their vocal learning abilities, gregarious nature, and reliance on vocalizations for social communication and navigation, bats represent an intriguing mammalian system in which to explore language‐relevant genes. We used immunohistochemistry to detail the distribution of FoxP2, FoxP1, and Cntnap2 proteins, accompanied by detailed cytoarchitectural histology in the brains of two vocal learning bat species; Phyllostomus discolor and Rousettus aegyptiacus. We show widespread expression of these genes, similar to what has been previously observed in other species, including humans. A striking difference was observed in the adult P. discolor bat, which showed low levels of FoxP2 expression in the cortex that contrasted with patterns found in rodents and nonhuman primates. We created an online, open‐access database within which all data can be browsed, searched, and high resolution images viewed to single cell resolution. The data presented herein reveal regions of interest in the bat brain and provide new opportunities to address the role of these language‐related genes in complex vocal‐motor and vocal learning behaviors in a mammalian model system.

Rostro-Caudal Organization of Connectivity between Cingulate Motor Areas and Lateral Frontal Regions

According to contemporary views, the lateral frontal cortex is organized along a rostro-caudal functional axis with increasingly complex cognitive/behavioral control implemented rostrally, and increasingly detailed motor control implemented caudally. Whether the medial frontal cortex follows the same organization remains to be elucidated. To address this issue, the functional connectivity of the 3 cingulate motor areas (CMAs) in the human brain with the lateral frontal cortex was investigated. First, the CMAs and their representations of hand, tongue, and eye movements were mapped via task-related functional magnetic resonance imaging (fMRI). Second, using resting-state fMRI, their functional connectivity with lateral prefrontal and lateral motor cortical regions of interest (ROIs) were examined. Importantly, the above analyses were conducted at the single-subject level to account for variability in individual cingulate morphology. The results demonstrated a rostro-caudal functional organization of the CMAs in the human brain that parallels that in the lateral frontal cortex: the rostral CMA has stronger functional connectivity with prefrontal regions and weaker connectivity with motor regions; conversely, the more caudal CMAs have weaker prefrontal and stronger motor connectivity. Connectivity patterns of the hand, tongue and eye representations within the CMAs are consistent with that of their parent CMAs. The parallel rostral-to-caudal functional organization observed in the medial and lateral frontal cortex could likely contribute to different hierarchies of cognitive-motor control.