Hemodynamic responses to speech and music in newborn infants

Syncopation as structure bootstrapping: the role of asymmetry in rhythm and language

Syncopation - the occurrence of a musical event on a metrically weak position preceding a rest on a metrically strong position - represents an important challenge in the study of the mapping between rhythm and meter. In this contribution, we present the hypothesis that syncopation is an effective strategy to elicit the bootstrapping of a multi-layered, hierarchically organized metric structure from a linear rhythmic surface. The hypothesis is inspired by a parallel with the problem of linearization in natural language syntax, which is the problem of how hierarchically organized phrase-structure markers are mapped onto linear sequences of words. The hypothesis has important consequences for the role of meter in music perception and cognition and, more particularly, for its role in the relationship between rhythm and bodily entrainment.

Preliminary evidence for selective cortical responses to music in one-month-old infants

Prior studies have observed selective neural responses in the adult human auditory cortex to music and speech that cannot be explained by the differing lower-level acoustic properties of these stimuli. Does infant cortex exhibit similarly selective responses to music and speech shortly after birth? To answer this question, we attempted to collect functional magnetic resonance imaging (fMRI) data from 45 sleeping infants (2.0- to 11.9-weeks-old) while they listened to monophonic instrumental lullabies and infant-directed speech produced by a mother. To match acoustic variation between music and speech sounds we (1) recorded music from instruments that had a similar spectral range as female infant-directed speech, (2) used a novel excitation-matching algorithm to match the cochleagrams of music and speech stimuli, and (3) synthesized "model-matched" stimuli that were matched in spectrotemporal modulation statistics to (yet perceptually distinct from) music or speech. Of the 36 infants we collected usable data from, 19 had significant activations to sounds overall compared to scanner noise. From these infants, we observed a set of voxels in non-primary auditory cortex (NPAC) but not in Heschl's Gyrus that responded significantly more to music than to each of the other three stimulus types (but not significantly more strongly than to the background scanner noise). In contrast, our planned analyses did not reveal voxels in NPAC that responded more to speech than to model-matched speech, although other unplanned analyses did. These preliminary findings suggest that music selectivity arises within the first month of life. A video abstract of this article can be viewed at https://youtu.be/c8IGFvzxudk. RESEARCH HIGHLIGHTS: Responses to music, speech, and control sounds matched for the spectrotemporal modulation-statistics of each sound were measured from 2- to 11-week-old sleeping infants using fMRI. Auditory cortex was significantly activated by these stimuli in 19 out of 36 sleeping infants. Selective responses to music compared to the three other stimulus classes were found in non-primary auditory cortex but not in nearby Heschl's Gyrus. Selective responses to speech were not observed in planned analyses but were observed in unplanned, exploratory analyses.

Sound Level Changes the Auditory Cortical Activation Detected with Functional Near-Infrared Spectroscopy

BACKGROUND

Functional near-infrared spectroscopy (fNIRS) is a viable non-invasive technique for functional neuroimaging in the cochlear implant (CI) population; however, the effects of acoustic stimulus features on the fNIRS signal have not been thoroughly examined. This study examined the effect of stimulus level on fNIRS responses in adults with normal hearing or bilateral CIs. We hypothesized that fNIRS responses would correlate with both stimulus level and subjective loudness ratings, but that the correlation would be weaker with CIs due to the compression of acoustic input to electric output.

METHODS

Thirteen adults with bilateral CIs and 16 with normal hearing (NH) completed the study. Signal-correlated noise, a speech-shaped noise modulated by the temporal envelope of speech stimuli, was used to determine the effect of stimulus level in an unintelligible speech-like stimulus between the range of soft to loud speech. Cortical activity in the left hemisphere was recorded.

RESULTS

Results indicated a positive correlation of cortical activation in the left superior temporal gyrus with stimulus level in both NH and CI listeners with an additional correlation between cortical activity and perceived loudness for the CI group. The results are consistent with the literature and our hypothesis.

CONCLUSIONS

These results support the potential of fNIRS to examine auditory stimulus level effects at a group level and the importance of controlling for stimulus level and loudness in speech recognition studies. Further research is needed to better understand cortical activation patterns for speech recognition as a function of both stimulus presentation level and perceived loudness.

Newborns modulate their crawling in response to their native language but not another language

Human newborns can propel themselves to their mother's breast when positioned skin to skin on her abdomen just after birth. For decades, researchers have considered this primitive crawling behavior a spinal reflex, immune to supra spinal control. However, recent research suggests that neonatal crawling is already responsive to visual and olfactory stimuli processed at a supra spinal level. Here we report that a few hours post birth, French newborns can also modulate their crawling in response to their native language - a source of information that is processed supra-spinally. The crawling patterns of 23 French-born newborns were recorded on video and via an infrared motion capture system during two randomly ordered 2-min trials. The newborns were secured on a mini skateboard to facilitate arm and leg movements during their crawling propulsion. They heard a repetitive sequence of the same sentences either in French, their native language, or in English, a rhythmically different and hence discriminable unfamiliar language, on each trial. In French, compared to English, crawling was enhanced, with significantly more arm and leg steps and significantly more and larger trunk rotations in the cephalo-caudal axis. Moreover, newborns rotated their heads and trunk toward the appropriate loud speaker when hearing French but not English. These preliminary findings suggest that newborn crawling is not a simple stereotyped reflex under spinal control, but a complex pattern that can be modulated in response to higher-order, supra-spinally processed stimuli. The findings open fascinating questions about the range of stimuli to which newborn crawling is responsive.

On the representation of hierarchical structure: Revisiting Darwin's musical protolanguage

In this article, we address the tenability of Darwin's musical protolanguage, arguing that a more compelling evolutionary scenario is one where a prosodic protolanguage is taken to be the preliminary step to represent the hierarchy involved in linguistic structures within a linear auditory signal. We hypothesize that the establishment of a prosodic protolanguage results from an enhancement of a rhythmic system that transformed linear signals into speech prosody, which in turn can mark syntactic hierarchical relations. To develop this claim, we explore the role of prosodic cues on the parsing of syntactic structures, as well as neuroscientific evidence connecting the evolutionary development of music and linguistic capacities. Finally, we entertain the assumption that the capacity to generate hierarchical structure might have developed as part of tool-making in human prehistory, and hence was established prior to the enhancement of a prosodic protolinguistic system.

Evaluation of the Short-Term Music Therapy on Brain Functions of Preterm Infants Using Functional Near-Infrared Spectroscopy

Music contains substantial contents that humans can perceive and thus has the capability to evoke positive emotions. Even though neonatal intensive care units (NICUs) can provide preterm infants a developmental environment, they still cannot fully simulate the environment in the womb. The reduced maternal care would increase stress levels in premature infants. Fortunately, music intervention has been proved that it can improve the NICU environment, such as stabilize the heart rate and the respiratory rate, reduce the incidence of apnea, and improve feeding. However, the effects of music therapy on the brain development of preterm infants need to be further investigated. In this paper, we evaluated the influence of short-term music therapy on the brain functions of preterm infants measured by functional near-infrared spectroscopy (fNIRS). We began by investigating how premature babies perceive structural information of music by calculating the correlations between music features and fNIRS signals. Then, the influences of short-term music therapy on brain functions were evaluated by comparing the resting-state functional connectivity before and after the short-term music therapy. The results show that distinct brain regions are responsible for processing corresponding musical features, indicating that preterm infants have the capability to process the complex musical content. However, the results of network analysis show that short-term music intervention is insufficient to cause the changes in cerebral functional connectivity. Therefore, long-term music therapy may be required to achieve the deserved effects on brain functional connectivity.

Hearing brain evaluated using near-infrared spectroscopy in congenital toxoplasmosis

Congenital toxoplasmosis (CT) is a known cause of hearing loss directly caused by Toxoplasma gondii. Hearing loss might result from sensory, neural, or sensorineural lesions. Early treated infants rarely develop hearing loss, but retinochoroidal lesions, intracranial calcifications and hydrocephalus are common. In this study, we aimed to evaluate the brain evoked hemodynamic responses of CT and healthy infants during four auditory stimuli: mother infant directed speech, researcher infant directed speech, mother reading and researcher recorded. Children underwent Transitionally Evoked Otoacoustic Emission Auditory Testing and Automated Brainstem Auditory Response tests with normal auditory results, but with a tendency for greater latencies in the CT group compared to the control group. We assessed brain hemodynamics with functional near-infrared spectroscopy (fNIRS) measurements from 61 infants, and we present fNIRS results as frequency maps of activation and deactivation for each stimulus. By evaluating infants in the three first months of life, we observed an individual heterogeneous brain activation pattern in response to all auditory stimuli for both groups. Each channel was activated or deactivated in less than 30% of children for all stimuli. There is a need of prospective studies to evaluate if the neurologic or auditory changes course with compromise of children outcomes.

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.

The Neurophysiological Processing of Music in Children: A Systematic Review With Narrative Synthesis and Considerations for Clinical Practice in Music Therapy

Introduction: Evidence supporting the use of music interventions to maximize arousal and awareness in adults presenting with a disorder of consciousness continues to grow. However, the brain of a child is not simply a small adult brain, and therefore adult theories are not directly translatable to the pediatric population. The present study aims to synthesize brain imaging data about the neural processing of music in children aged 0-18 years, to form a theoretical basis for music interventions with children presenting with a disorder of consciousness following acquired brain injury. Methods: We conducted a systematic review with narrative synthesis utilizing an adaptation of the methodology developed by Popay and colleagues. Following the development of the narrative that answered the central question "what does brain imaging data reveal about the receptive processing of music in children?", discussion was centered around the clinical implications of music therapy with children following acquired brain injury. Results: The narrative synthesis included 46 studies that utilized EEG, MEG, fMRI, and fNIRS scanning techniques in children aged 0-18 years. From birth, musical stimuli elicit distinct but immature electrical responses, with components of the auditory evoked response having longer latencies and variable amplitudes compared to their adult counterparts. Hemodynamic responses are observed throughout cortical and subcortical structures however cortical immaturity impacts musical processing and the localization of function in infants and young children. The processing of complex musical stimuli continues to mature into late adolescence. Conclusion: While the ability to process fundamental musical elements is present from birth, infants and children process music more slowly and utilize different cortical areas compared to adults. Brain injury in childhood occurs in a period of rapid development and the ability to process music following brain injury will likely depend on pre-morbid musical processing. Further, a significant brain injury may disrupt the developmental trajectory of complex music processing. However, complex music processing may emerge earlier than comparative language processing, and occur throughout a more global circuitry.

Structural and functional brain asymmetries in the early phases of life: a scoping review

Asymmetry characterizes the brain in both structure and function. Anatomical asymmetries explain only a fraction of functional variability in lateralization, with structural and functional asymmetries developing at different periods of life and in different ways. In this work, we perform a scoping review of the cerebral asymmetries in the first brain development phases. We included all English-written studies providing direct evidence of hemispheric asymmetries in full-term neonates, foetuses, and premature infants, both at term post-conception and before. The final analysis included 57 studies. The reviewed literature shows large variability in the used techniques and methodological procedures. Most structural studies investigated the temporal lobe, showing a temporal planum more pronounced on the left than on the right (although not all data agree), a morphological asymmetry already present from the 29th week of gestation. Other brain structures have been poorly investigated, and the results are even more discordant. Unlike data on structural asymmetries, functional data agree with each other, identifying a leftward dominance for speech stimuli and an overall dominance of the right hemisphere in all other functional conditions. This generalized dominance of the right hemisphere for all conditions (except linguistic stimuli) is in line with theories stating that the right hemisphere develops earlier and that its development is less subject to external influences because it sustains functions necessary to survive.

Sleep, Little Baby: The Calming Effects of Prenatal Speech Exposure on Newborns' Sleep and Heartrate

In a pilot study, 34 fetuses were stimulated daily with a maternal spoken nursery rhyme from week 34 of gestation onward and re-exposed two and five weeks after birth to this familiar, as well as to an unfamiliar rhyme, both spoken with the maternal and an unfamiliar female voice. During auditory stimulation, newborns were continuously monitored with polysomnography using video-monitored hdEEG. Afterward, changes in sleep–wake-state proportions during familiar and unfamiliar voice stimulation were analyzed. Our preliminary results demonstrate a general calming effect of auditory stimulation exclusively in infants who were prenatally “familiarized” with a spoken nursery rhyme, as evidenced by less waking states, more time spent in quiet (deep) sleep, and lower heartrates. A stimulation naïve group, on the other hand, demonstrated no such effects. Stimulus-specific effects related to the familiarity of the prenatally replayed voice or rhyme were not evident in newborns. Together, these results suggest “fetal learning” at a basic level and point to a familiarization with auditory stimuli prior to birth, which is evident in the first weeks of life in behavioral states and heartrate physiology of the newborn.

Language Cerebro-cerebellar Reorganization in Children After Surgery of Right Cerebellar Astrocytoma: a fMRI Study

Language processing depends on an integrated circuit involving the left supratentorial language areas and the right posterior lateral cerebellar hemisphere (lobule VI, lobule VII, Crus I, and Crus II). Reorganization of the language system after lesions of the cerebral language areas includes also cerebellar relocation. This is the first study assessing functional language reorganization after lesions concerning primarily the cerebellum, using a fMRI paradigm of phonological covert word production task in six children operated for right cerebellar astrocytoma and in 15 typically developing children. We found right cerebellar and left frontal activations in healthy controls and high variability of reorganizational patterns in patients with early right cerebellar lesion. Also lesions not located in the areas typically involved in language tasks (Crus I and Crus II) can cause reorganization between the two hemispheres or hemispheric language reinforcement of the original lateralization. We discuss the role of several variables in determining the reorganizational pattern such as the site, extension, and timing of surgery. No variables revealed as predictors, suggesting that co-occurring influence of other biological and/or pathological factors are not yet demonstrated. Lesions in the postero-lateral cerebellum seem related to less efficient language performances, as an indicator of the system's functioning.

Hemodynamic responses to emotional speech in two-month-old infants imaged using diffuse optical tomography

Emotional speech is one of the principal forms of social communication in humans. In this study, we investigated neural processing of emotional speech (happy, angry, sad and neutral) in the left hemisphere of 21 two-month-old infants using diffuse optical tomography. Reconstructed total hemoglobin (HbT) images were analysed using adaptive voxel-based clustering and region-of-interest (ROI) analysis. We found a distributed happy > neutral response within the temporo-parietal cortex, peaking in the anterior temporal cortex; a negative HbT response to emotional speech (the average of the emotional speech conditions < baseline) in the temporo-parietal cortex, neutral > angry in the anterior superior temporal sulcus (STS), happy > angry in the superior temporal gyrus and posterior superior temporal sulcus, angry < baseline in the insula, superior temporal sulcus and superior temporal gyrus and happy < baseline in the anterior insula. These results suggest that left STS is more sensitive to happy speech as compared to angry speech, indicating that it might play an important role in processing positive emotions in two-month-old infants. Furthermore, happy speech (relative to neutral) seems to elicit more activation in the temporo-parietal cortex, thereby suggesting enhanced sensitivity of temporo-parietal cortex to positive emotional stimuli at this stage of infant development.

Investigation of the Pattern of the Hemodynamic Response as Measured by Functional Near-Infrared Spectroscopy (fNIRS) Studies in Newborns, Less Than a Month Old: A Systematic Review

It has been 20 years since functional near-infrared spectroscopy (fNIRS) was first used to investigate the evoked hemodynamic response to a stimulus in newborns. The hemodynamic response to functional activation is well-established in adults, with an observed increase in concentration change of oxygenated hemoglobin (Δ[HbO2]) and decrease in deoxygenated hemoglobin (Δ[HHb]). However, functional studies in newborns have revealed a mixed response, particularly with Δ[HHb] where an inconsistent change in direction is observed. The reason for this heterogeneity is unknown, with potential explanations arising from differing physiology in the developing brain, or differences in instrumentation or methodology. The aim of this review is to collate the findings from studies that have employed fNIRS to monitor cerebral hemodynamics in term newborn infants aged 1 day-1 month. A total of 46 eligible studies were identified; some studies investigated more than one stimulus type, resulting in a total of 51 reported results. The NIRS parameters reported varied across studies with 50/51 cases reporting Δ[HbO2], 39/51 reporting Δ[HHb], and 13/51 reporting total hemoglobin concentration Δ[HbT] (Δ[HbO2] + Δ[HHb]). However, of the 39 cases reporting Δ[HHb] in graphs or tables, only 24 studies explicitly discussed the response (i.e., direction of change) of this variable. In the studies where the fNIRS responses were discussed, 46/51 cases observed an increase in Δ[HbO2], 7/51 observed an increase or varied Δ[HHb], and 2/51 reported a varied or negative Δ[HbT]. An increase in Δ[HbO2] and decrease or no change in Δ[HHb] was observed in 15 studies. By reviewing this body of literature, we have identified that the majority of research articles reported an increase in Δ[HbO2] across various functional tasks and did not report the response of Δ[HHb]. Confirming the normal, healthy hemodynamic response in newborns will allow identification of unhealthy patterns and their association to normal neurodevelopment.

Neonatal eyelid conditioning during sleep

Using an eyelid conditioning paradigm modeled after that developed by Little, Lipsitt, and Rovee-Collier (1984), Fifer et al. (2010) demonstrated that newborn infants learn during sleep. This study examined the role of sleep state in neonatal learning. We recorded electroencephalogram (EEG), respiratory, and cardiovascular activity from sleeping full term newborn infants during delay eyelid conditioning. In the experimental group (n = 21), a tone was paired with an air puff to the eye. Consistent with Fifer et al. (2010), newborn infants reliably learned during sleep. The experimental group more than doubled EMR rates to a tone alone, while a control group (n = 17) presented with unpaired tones and puffs maintained low EMR rates. Infant learners were more likely to produce a conditioned EMR during quiet sleep compared to active sleep. Understanding the influence of sleep state on conditioned responses will inform the potential use of eyelid conditioning for early screening.

fNIRS in the developmental sciences

With the introduction of functional near-infrared spectroscopy (fNIRS) into the experimental setting, developmental scientists have, for the first time, the capacity to investigate the functional activation of the infant brain in awake, engaged participants. The advantages of fNIRS clearly outweigh the limitations, and a description of how this technology is implemented in infant populations is provided. Most fNIRS research falls into one of three content domains: object processing, processing of biologically and socially relevant information, and language development. Within these domains, there are ongoing debates about the origins and development of human knowledge, making early neuroimaging particularly advantageous. The use of fNIRS has allowed investigators to begin to identify the localization of early object, social, and linguistic knowledge in the immature brain and the ways in which this changes with time and experience. In addition, there is a small but growing body of research that provides insight into the neural mechanisms that support and facilitate learning during the first year of life. At the same time, as with any emerging field, there are limitations to the conclusions that can be drawn on the basis of current findings. We offer suggestions as to how to optimize the use of this technology to answer questions of theoretical and practical importance to developmental scientists.

Responses to vocalizations and auditory controls in the human newborn brain

In the adult brain, speech can recruit a brain network that is overlapping with, but not identical to, that involved in perceiving non-linguistic vocalizations. Using the same stimuli that had been presented to human 4-month-olds and adults, as well as adult macaques, we sought to shed light on the cortical networks engaged when human newborns process diverse vocalization types. Near infrared spectroscopy was used to register the response of 40 newborns' perisylvian regions when stimulated with speech, human and macaque emotional vocalizations, as well as auditory controls where the formant structure was destroyed but the long-term spectrum was retained. Left fronto-temporal and parietal regions were significantly activated in the comparison of stimulation versus rest, with unclear selectivity in cortical activation. These results for the newborn brain are qualitatively and quantitatively compared with previous work on newborns, older human infants, adult humans, and adult macaques reported in previous work.

Precursors of dancing and singing to music in three- to four-months-old infants

Dancing and singing to music involve auditory-motor coordination and have been essential to our human culture since ancient times. Although scholars have been trying to understand the evolutionary and developmental origin of music, early human developmental manifestations of auditory-motor interactions in music have not been fully investigated. Here we report limb movements and vocalizations in three- to four-months-old infants while they listened to music and were in silence. In the group analysis, we found no significant increase in the amount of movement or in the relative power spectrum density around the musical tempo in the music condition compared to the silent condition. Intriguingly, however, there were two infants who demonstrated striking increases in the rhythmic movements via kicking or arm-waving around the musical tempo during listening to music. Monte-Carlo statistics with phase-randomized surrogate data revealed that the limb movements of these individuals were significantly synchronized to the musical beat. Moreover, we found a clear increase in the formant variability of vocalizations in the group during music perception. These results suggest that infants at this age are already primed with their bodies to interact with music via limb movements and vocalizations.

Music processing similarities between sleeping newborns and alert adults: cause for celebration or concern?

[This corrects the article on p. 492 in vol. 4, PMID: 23966962.].

Music and speech prosody: a common rhythm

Disorders of music and speech perception, known as amusia and aphasia, have traditionally been regarded as dissociated deficits based on studies of brain damaged patients. This has been taken as evidence that music and speech are perceived by largely separate and independent networks in the brain. However, recent studies of congenital amusia have broadened this view by showing that the deficit is associated with problems in perceiving speech prosody, especially intonation and emotional prosody. In the present study the association between the perception of music and speech prosody was investigated with healthy Finnish adults (n = 61) using an on-line music perception test including the Scale subtest of Montreal Battery of Evaluation of Amusia (MBEA) and Off-Beat and Out-of-key tasks as well as a prosodic verbal task that measures the perception of word stress. Regression analyses showed that there was a clear association between prosody perception and music perception, especially in the domain of rhythm perception. This association was evident after controlling for music education, age, pitch perception, visuospatial perception, and working memory. Pitch perception was significantly associated with music perception but not with prosody perception. The association between music perception and visuospatial perception (measured using analogous tasks) was less clear. Overall, the pattern of results indicates that there is a robust link between music and speech perception and that this link can be mediated by rhythmic cues (time and stress).

Insights on NIRS Sensitivity from a Cross-Linguistic Study on the Emergence of Phonological Grammar

Each language has a unique set of phonemic categories and phonotactic rules which determine permissible sound sequences in that language. Behavioral research demonstrates that one's native language shapes the perception of both sound categories and sound sequences in adults, and neuroimaging results further indicate that the processing of native phonemes and phonotactics involves a left-dominant perisylvian brain network. Recent work using a novel technique, functional Near InfraRed Spectroscopy (NIRS), has suggested that a left-dominant network becomes evident toward the end of the first year of life as infants process phonemic contrasts. The present research project attempted to assess whether the same pattern would be seen for native phonotactics. We measured brain responses in Japanese- and French-learning infants to two contrasts: Abuna vs. Abna (a phonotactic contrast that is native in French, but not in Japanese) and Abuna vs. Abuuna (a vowel length contrast that is native in Japanese, but not in French). Results did not show a significant response to either contrast in either group, unlike both previous behavioral research on phonotactic processing and NIRS work on phonemic processing. To understand these null results, we performed similar NIRS experiments with Japanese adult participants. These data suggest that the infant null results arise from an interaction of multiple factors, involving the suitability of the experimental paradigm for NIRS measurements and stimulus perceptibility. We discuss the challenges facing this novel technique, particularly focusing on the optimal stimulus presentation which could yield strong enough hemodynamic responses when using the change detection paradigm.

An online database of infant functional near infrared spectroscopy studies: a community-augmented systematic review

Until recently, imaging the infant brain was very challenging. Functional Near InfraRed Spectroscopy (fNIRS) is a promising, relatively novel technique, whose use is rapidly expanding. As an emergent field, it is particularly important to share methodological knowledge to ensure replicable and robust results. In this paper, we present a community-augmented database which will facilitate precisely this exchange. We tabulated articles and theses reporting empirical fNIRS research carried out on infants below three years of age along several methodological variables. The resulting spreadsheet has been uploaded in a format allowing individuals to continue adding new results, and download the most recent version of the table. Thus, this database is ideal to carry out systematic reviews. We illustrate its academic utility by focusing on the factors affecting three key variables: infant attrition, the reliability of oxygenated and deoxygenated responses, and signal-to-noise ratios. We then discuss strengths and weaknesses of the DBIfNIRS, and conclude by suggesting a set of simple guidelines aimed to facilitate methodological convergence through the standardization of reports.

Music and early language acquisition

Language is typically viewed as fundamental to human intelligence. Music, while recognized as a human universal, is often treated as an ancillary ability - one dependent on or derivative of language. In contrast, we argue that it is more productive from a developmental perspective to describe spoken language as a special type of music. A review of existing studies presents a compelling case that musical hearing and ability is essential to language acquisition. In addition, we challenge the prevailing view that music cognition matures more slowly than language and is more difficult; instead, we argue that music learning matches the speed and effort of language acquisition. We conclude that music merits a central place in our understanding of human development.

A failure of left temporal cortex to specialize for language is an early emerging and fundamental property of autism

Failure to develop normal language comprehension is an early warning sign of autism, but the neural mechanisms underlying this signature deficit are unknown. This is because of an almost complete absence of functional studies of the autistic brain during early development. Using functional magnetic resonance imaging, we previously observed a trend for abnormally lateralized temporal responses to language (i.e. greater activation on the right, rather than the expected left) in a small sample (n = 12) of sleeping 2-3 year olds with autism in contrast to typically developing children, a finding also reported in autistic adults and adolescents. It was unclear, however, if findings of atypical laterality would be observed in a larger sample, and at even earlier ages in autism, such as around the first birthday. Answers to these questions would provide the foundation for understanding how neurofunctional defects of autism unfold, and provide a foundation for studies using patterns of brain activation as a functional early biomarker of autism. To begin to examine these issues, a prospective, cross-sectional design was used in which brain activity was measured in a large sample of toddlers (n = 80) during the presentation of a bedtime story during natural sleep. Forty toddlers with autism spectrum disorder and 40 typically developing toddlers ranging in age between 12-48 months participated. Any toddler with autism who participated in the imaging experiment prior to final diagnosis was tracked and diagnoses confirmed at a later age. Results indicated that at-risk toddlers later diagnosed as autistic display deficient left hemisphere response to speech sounds and have abnormally right-lateralized temporal cortex response to language; this defect worsens with age, becoming most severe in autistic 3- and 4-year-olds. Typically developing children show opposite developmental trends with a tendency towards greater temporal cortex response with increasing age and maintenance of left-lateralized activation with age. We have now demonstrated lateralized abnormalities of temporal cortex processing of language in autism across two separate samples, including a large sample of young infants who later are diagnosed with autism, suggesting that this pattern may reflect a fundamental early neural developmental pathology in autism.

Influence of gestational age and postnatal age on speech sound processing in NICU infants

The study examined the effect of gestational (GA) and postnatal (PNA) age on speech sound perception in infants. Auditory event-related potentials (ERPs) were recorded in response to speech sounds (syllables) in 50 infant NICU patients (born at 24-40 weeks gestation) prior to discharge. Efficiency of speech perception was quantified as absolute difference in mean amplitudes of ERPs in response to vowel (/a/-/u/) and consonant (/b/-/g/, /d/-/g/) contrasts within 150-250, 250-400, 400-700 ms after stimulus onset. Results indicated that both GA and PNA affected speech sound processing. These effects were more pronounced for consonant than vowel contrasts. Increasing PNA was associated with greater sound discrimination in infants born at or after 30 weeks GA, while minimal PNA-related changes were observed for infants with GA less than 30 weeks. Our findings suggest that a certain level of brain maturity at birth is necessary to benefit from postnatal experience in the first 4 months of life, and both gestational and postnatal ages need to be considered when evaluating infant brain responses.

Questioning the questions that have been asked about the infant brain using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a noninvasive diffuse optical-imaging technique that can measure local metabolic demand in the surface of the cortex due to differential absorption of light by oxygenated and deoxygenated blood. Over the past decade, NIRS has become increasingly used as a complement to other neuroimaging techniques, such as electroencephalography (EEG), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI), particularly in paediatric populations who cannot easily be tested using fMRI and MEG. In this review of empirical findings from human infants, ranging in age from birth to 12 months of age, a number of interpretive concerns are raised about what can be concluded from NIRS data. In addition, inconsistencies across studies are highlighted, and strategies are proposed for enhancing the reliability of NIRS data gathered from infants. Finally, a variety of new and promising advances in NIRS techniques are highlighted.

Linking behavioral and neurophysiological indicators of perceptual tuning to language

Little is known about the neural mechanisms that underlie tuning to the native language(s) in early infancy. Here we review language tuning through the lens of type and amount of language experience and introduce a new manner in which to conceptualize the phenomenon of language tuning: the relative speed of tuning hypothesis. This hypothesis has as its goal a characterization of the unique time course of the tuning process, given the different components (e.g., phonology, prosody, syntax, semantics) of one or more languages as they become available to infants, and biologically based maturational constraints. In this review, we first examine the established behavioral findings and integrate more recent neurophysiological data on neonatal development, which together demonstrate evidence of early language tuning given differential language exposure even in utero. Next, we examine traditional accounts of sensitive and critical periods to determine how these constructs complement current data on the neural mechanisms underlying language tuning. We then synthesize the extant infant behavioral and neurophysiological data on monolingual, bilingual, and sensory deprived tuning, thereby scrutinizing the effect of these three different language profiles on the specific timing, progression, and outcome of language tuning. Finally, we discuss future directions researchers might pursue to further understand this aspect of language development, advocating our relative speed of tuning hypothesis as a useful framework for conceptualizing the complex process by which language experience works together with biological constraints to shape language development.

Cerebral hemodynamics in newborn infants exposed to speech sounds: a whole-head optical topography study

Considerable knowledge on neural development related to speech perception has been obtained by functional imaging studies using near-infrared spectroscopy (optical topography). In particular, a pioneering study showed stronger left-dominant activation in the temporal lobe for (normal) forward speech (FW) than for (reversed) backward speech (BW) in neonates. However, it is unclear whether this stronger left-dominant activation for FW is equally observed for any language or is clearer for the mother tongue. We hypothesized that the maternal language elicits clearer activation than a foreign language in newborns because of their prenatal and/or few-day postnatal exposure to the maternal language. To test this hypothesis, we developed a whole-head optode cap for 72-channel optical topography and visualized the spatiotemporal hemodynamics in the brains of 17 Japanese newborns when they were exposed to FW and BW in their maternal language (Japanese) and in a foreign language (English). Statistical analysis showed that all sound stimuli together induced significant activation in the bilateral temporal regions and the frontal region. They also showed that the left temporal-parietal region was significantly more active for Japanese FW than Japanese BW or English FW, while no significant difference between FW and BW was shown for English. This supports our hypothesis and suggests that the few-day-old brain begins to become attuned to the maternal language. Together with a finding of equivalent activation for all sound stimuli in the adjacent measurement positions in the temporal region, these findings further clarify the functional organization of the neonatal brain.

A linear structural equation model for covert verb generation based on independent component analysis of FMRI data from children and adolescents

Human language is a complex and protean cognitive ability. Young children, following well defined developmental patterns learn language rapidly and effortlessly producing full sentences by the age of 3 years. However, the language circuitry continues to undergo significant neuroplastic changes extending well into teenage years. Evidence suggests that the developing brain adheres to two rudimentary principles of functional organization: functional integration and functional specialization. At a neurobiological level, this distinction can be identified with progressive specialization or focalization reflecting consolidation and synaptic reinforcement of a network (Lenneberg, 1967; Muller et al., 1998; Berl et al., 2006). In this paper, we used group independent component analysis and linear structural equation modeling (McIntosh and Gonzalez-Lima, 1994; Karunanayaka et al., 2007) to tease out the developmental trajectories of the language circuitry based on fMRI data from 336 children ages 5–18 years performing a blocked, covert verb generation task. The results are analyzed and presented in the framework of theoretical models for neurocognitive brain development. This study highlights the advantages of combining both modular and connectionist approaches to cognitive functions; from a methodological perspective, it demonstrates the feasibility of combining data-driven and hypothesis driven techniques to investigate the developmental shifts in the semantic network.

Large-scale brain networks underlying language acquisition in early infancy

A critical issue in human development is that of whether the language-related areas in the left frontal and temporal regions work as a functional network in preverbal infants. Here, we used 94-channel near-infrared spectroscopy to reveal the functional networks in the brains of sleeping 3-month-old infants with and without presenting speech sounds. During the first 3 min, we measured spontaneous brain activation (period 1). After period 1, we provided stimuli by playing Japanese sentences for 3 min (period 2). Finally, we measured brain activation for 3 min without providing the stimulus (period 3), as in period 1. We found that not only the bilateral temporal and temporoparietal regions but also the prefrontal and occipital regions showed oxygenated hemoglobin signal increases and deoxygenated hemoglobin signal decreases when speech sounds were presented to infants. By calculating time-lagged cross-correlations and coherences of oxy-Hb signals between channels, we tested the functional connectivity for the three periods. The oxy-Hb signals in neighboring channels, as well as their homologous channels in the contralateral hemisphere, showed high correlation coefficients in period 1. Similar correlations were observed in period 2; however, the number of channels showing high correlations was higher in the ipsilateral hemisphere, especially in the anterior–posterior direction. The functional connectivity in period 3 showed a close relationship between the frontal and temporal regions, which was less prominent in period 1, indicating that these regions form the functional networks and work as a hysteresis system that has memory of the previous inputs. We propose a hypothesis that the spatiotemporally large-scale brain networks, including the frontal and temporal regions, underlie speech processing in infants and they might play important roles in language acquisition during infancy.

Functional development in the infant brain for auditory pitch processing

Understanding how the developing brain processes auditory information is a critical step toward the clarification of infants' perception of speech and music. We have reported that the infant brain perceives pitch information in speech sounds. Here, we used multichannel near-infrared spectroscopy to examine whether the infant brain is sensitive to information of pitch changes in auditory sequences. Three types of auditory sequences with distinct temporal structures of pitch changes were presented to 3- and 6-month-old infants: a long condition of 12 successive tones constructing a chromatic scale (600 ms), a short condition of four successive tones constructing a chromatic scale (200 ms), and a random condition of random tone sequences (50 ms per tone). The difference among the conditions was only in the sequential order of the tones, which causes pitch changes between the successive tones. We found that the bilateral temporal regions of both ages of infants showed significant activation under the three conditions. The stimulus-dependent activation was observed in the right temporoparietal region of the both infant groups; the 3- and 6-month-old infants showed the most prominent activation under the random and short conditions, respectively. Our findings indicate that the infant brain, which shows functional differentiation and lateralization in auditory-related areas, is capable of responding to more than single tones of pitch information. These results suggest that the right temporoparietal region of the infants increases sensitivity to auditory sequences, which have temporal structures similar to those of syllables in speech sounds, in the course of development.

Assessment of the frequency-domain multi-distance method to evaluate the brain optical properties: Monte Carlo simulations from neonate to adult

The near infrared spectroscopy (NIRS) frequency-domain multi-distance (FD-MD) method allows for the estimation of optical properties in biological tissue using the phase and intensity of radiofrequency modulated light at different source-detector separations. In this study, we evaluated the accuracy of this method to retrieve the absorption coefficient of the brain at different ages. Synthetic measurements were generated with Monte Carlo simulations in magnetic resonance imaging (MRI)-based heterogeneous head models for four ages: newborn, 6 and 12 month old infants, and adult. For each age, we determined the optimal set of source-detector separations and estimated the corresponding errors. Errors arise from different origins: methodological (FD-MD) and anatomical (curvature, head size and contamination by extra-cerebral tissues). We found that the brain optical absorption could be retrieved with an error between 8-24% in neonates and infants, while the error increased to 19-44% in adults over all source-detector distances. The dominant contribution to the error was found to be the head curvature in neonates and infants, and the extra-cerebral tissues in adults.