Early development of brain responses to rapidly presented auditory stimulation: a magnetoencephalographic study

Tracking evoked responses to auditory and visual stimuli in fetuses exposed to maternal high-risk conditions

Magnetoencephalography (MEG) has been successfully applied to record fetal auditory (auditory evoked response [AER]) and visual evoked responses (VER). In this study, we report the AER and VER development trajectory by tracking the evoked response detectability and latency from recordings starting at 27 weeks of gestation in pregnancies classified as high risk. Fetal MEG and ultrasound recordings were performed on 158 pregnant women, and the total number of fetal auditory and visual tests conducted was 321 and 237, respectively. The overall evoked response analysis showed 237 AER (73.8%) and 164 VER detections (69.2%). The mean AER latency was 290.7 (SD 125.5) ms and the mean VER latency was 293.7 (SD 114.5) ms. The rate of decrease (95% confidence limits) in average AER and VER first-peak latency between 100-350 ms was 1.97 (-1.86, +5.81) ms/week and 1.35 (-3.83, +6.53) ms/week, respectively. This trend in high-risk fetuses conforms to the general trajectory of decrease in latency with gestational age progression, even though this decrease was non-significant, as reported in the case of normal growing fetuses. Although there was a significant difference in detection rates between male and female fetuses, this was not reflected in either latency values or the sensory modality applied. Furthermore, the main factors that had the most significant effect on response detectability included the presence of intervening layers of adipose tissue between the fetal head and stimulus source and an increase in the maternal body mass index.

Magnetic Source Imaging and Infant MEG: Current Trends and Technical Advances

Magnetoencephalography (MEG) is known for its temporal precision and good spatial resolution in cognitive brain research. Nonetheless, it is still rarely used in developmental research, and its role in developmental cognitive neuroscience is not adequately addressed. The current review focuses on the source analysis of MEG measurement and its potential to answer critical questions on neural activation origins and patterns underlying infants’ early cognitive experience. The advantages of MEG source localization are discussed in comparison with functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS), two leading imaging tools for studying cognition across age. Challenges of the current MEG experimental protocols are highlighted, including measurement and data processing, which could potentially be resolved by developing and improving both software and hardware. A selection of infant MEG research in auditory, speech, vision, motor, sleep, cross-modality, and clinical application is then summarized and discussed with a focus on the source localization analyses. Based on the literature review and the advancements of the infant MEG systems and source analysis software, typical practices of infant MEG data collection and analysis are summarized as the basis for future developmental cognitive research.

Exploring early human brain development with structural and physiological neuroimaging

Early brain development, from the embryonic period to infancy, is characterized by rapid structural and functional changes. These changes can be studied using structural and physiological neuroimaging methods. In order to optimally acquire and accurately interpret this data, concepts from adult neuroimaging cannot be directly transferred. Instead, one must have a basic understanding of fetal and neonatal structural and physiological brain development, and the important modulators of this process. Here, we first review the major developmental milestones of transient cerebral structures and structural connectivity (axonal connectivity) followed by a summary of the contributions from ex vivo and in vivo MRI. Next, we discuss the basic biology of neuronal circuitry development (synaptic connectivity, i.e. ensemble of direct chemical and electrical connections between neurons), physiology of neurovascular coupling, baseline metabolic needs of the fetus and the infant, and functional connectivity (defined as statistical dependence of low-frequency spontaneous fluctuations seen with functional magnetic resonance imaging (fMRI)). The complementary roles of magnetic resonance imaging (MRI), electroencephalography (EEG), magnetoencephalography (MEG), and near-infrared spectroscopy (NIRS) are discussed. We include a section on modulators of brain development where we focus on the placenta and emerging placental MRI approaches. In each section we discuss key technical limitations of the imaging modalities and some of the limitations arising due to the biology of the system. Although neuroimaging approaches have contributed significantly to our understanding of early brain development, there is much yet to be done and a dire need for technical innovations and scientific discoveries to realize the future potential of early fetal and infant interventions to avert long term disease.

Magnetoencephalography and the infant brain

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that provides whole-head measures of neural activity with millisecond temporal resolution. Over the last three decades, MEG has been used for assessing brain activity, most commonly in adults. MEG has been used less often to examine neural function during early development, in large part due to the fact that infant whole-head MEG systems have only recently been developed. In this review, an overview of infant MEG studies is provided, focusing on the period from birth to three years. The advantages of MEG for measuring neural activity in infants are highlighted (See Box 1), including the ability to assess activity in brain (source) space rather than sensor space, thus allowing direct assessment of neural generator activity. Recent advances in MEG hardware and source analysis are also discussed. As the review indicates, efforts in this area demonstrate that MEG is a promising technology for studying the infant brain. As a noninvasive technology, with emerging hardware providing the necessary sensitivity, an expected deliverable is the capability for longitudinal infant MEG studies evaluating the developmental trajectory (maturation) of neural activity. It is expected that departures from neuro-typical trajectories will offer early detection and prognosis insights in infants and toddlers at-risk for neurodevelopmental disorders, thus paving the way for early targeted interventions.

Extremely preterm children exhibit increased interhemispheric connectivity for language: findings from fMRI-constrained MEG analysis

Children born extremely preterm are at significant risk for cognitive impairment, including language deficits. The relationship between preterm birth and neurological changes that underlie cognitive deficits is poorly understood. We use a stories-listening task in fMRI and MEG to characterize language network representation and connectivity in children born extremely preterm (n = 15, <28 weeks gestation, ages 4-6 years), and in a group of typically developing control participants (n = 15, term birth, 4-6 years). Participants completed a brief neuropsychological assessment. Conventional fMRI analyses revealed no significant differences in language network representation across groups (p > .05, corrected). The whole-group fMRI activation map was parcellated to define the language network as a set of discrete nodes, and the timecourse of neuronal activity at each position was estimated using linearly constrained minimum variance beamformer in MEG. Virtual timecourses were subjected to connectivity and network-based analyses. We observed significantly increased beta-band functional connectivity in extremely preterm compared to controls (p < .05). Specifically, we observed an increase in connectivity between left and right perisylvian cortex. Subsequent effective connectivity analyses revealed that hyperconnectivity in preterms was due to significantly increased information flux originating from the right hemisphere (p < 0.05). The total strength and density of the language network were not related to language or nonverbal performance, suggesting that the observed hyperconnectivity is a "pure" effect of prematurity. Although our extremely preterm children exhibited typical language network architecture, we observed significantly altered network dynamics, indicating reliance on an alternative neural strategy for the language task.

Antenatal Training with Music and Maternal Talk Concurrently May Reduce Autistic-Like Behaviors at around 3 Years of Age

Antenatal training through music and maternal talk to the unborn fetus is a topic of general interest for parents-to-be in China, but we still lack a comprehensive assessment of their effects on the development of autistic-like behaviors during early childhood. During 2014-2016, 34,749 parents of children around the age of 3 years who were enrolled at kindergarten in the Longhua district of Shenzhen participated in this study. Self-administered questionnaires regarding demographics, antenatal music training, and maternal talk to the fetus during pregnancy were completed by the children's primary caregivers. Autistic-like behaviors were assessed using the Autism Behavioral Checklist. Tobit regression analyses revealed that antenatal music training and maternal talk to the fetus was associated with a reduction in autistic-like behaviors in children, with a dose-dependent relationship. Furthermore, factorial analysis of covariance indicated a significant interaction effect between antenatal music training and maternal talk to the fetus on the autistic-like behaviors and found that children who often experienced antenatal music training and maternal talk concurrently had the lowest risk of autistic-like behaviors, while children who were never exposed to maternal talk and only sometimes experienced antenatal music training had the highest risk. Our results suggest that antenatal training through both music and maternal talk to the unborn fetus might reduce the risk of children's autistic-like behaviors at around 3 years of age.

W, Parlato-Oliveira EM. Estratégias de percepção da língua materna: do nascimento até um ano de vida

RESUMO Bebês muito jovens demonstram habilidades linguísticas bastante refinadas, sendo capazes de perceber várias características na fala do adulto. A percepção da língua materna é, pois, imprescindível para a aquisição da linguagem. Esta revisão de literatura trata das habilidades de percepção de fala dos bebês a partir do nascimento até um ano de idade. Para tanto, foi realizada a busca bibliográfica em 7 bases de dados, nos idiomas inglês, francês, português e espanhol, no período de 2007 a 2014. Com esse levantamento bibliográfico foi possível reconhecer como a aquisição da linguagem ocorre de forma rápida e que bebês bem jovens são capazes de utilizar estratégias elaboradas para iniciar tal aquisição.

The functional foetal brain: A systematic preview of methodological factors in reporting foetal visual and auditory capacity

Due to technological advancements in functional brain imaging, foetal brain responses to visual and auditory stimuli is a growing area of research despite being relatively small with much variation between research laboratories. A number of inconsistencies between studies are, nonetheless, present in the literature. This article aims to explore the potential contribution of methodological factors to variation in reports of foetal neural responses to external stimuli. Some of the variation in reports can be explained by methodological differences in aspects of study design, such as brightness and wavelength of light source. In contrast to visual foetal processing, auditory foetal processing has been more frequently investigated and findings are more consistent between different studies. This is an early preview of an emerging field with many articles reporting small sample sizes with techniques that are yet to be replicated. We suggest areas for improvement for the field as a whole, such as the standardisation of stimulus delivery and a more detailed reporting of methods and results. This will improve our understanding of foetal functional response to light and sound. We suggest that enhanced technology will allow for a more reliable description of the developmental trajectory of foetal processing of light stimuli.

Functional plasticity before the cradle: a review of neural functional imaging in the human fetus

The organization of the brain is highly plastic in fetal life. Establishment of healthy neural functional systems during the fetal period is essential to normal growth and development. Across the last several decades, remarkable progress has been made in understanding the development of human fetal functional brain systems. This is largely due to advances in imaging methodologies. Fetal neuroimaging began in the 1950-1970's with fetal electroencephalography (EEG) applied during labor. Later, in the 1980's, magnetoencephalography (MEG) emerged as an effective approach for investigating fetal brain function. Most recently, functional magnetic resonance imaging (fMRI) has arisen as an additional powerful approach for examining fetal brain function. This review will discuss major developmental findings from fetal imaging studies such as the maturation of prenatal sensory system functions, functional hemispheric asymmetry, and sensory-driven neurodevelopment. We describe how with improved imaging and analysis techniques, functional imaging of the fetus has the potential to assess the earliest point of neural maturation and provide insight into the patterning and sequence of normal and abnormal brain development.

Magnetoencephalography in neonatology

Magnetoencephalography (MEG) is a noninvasive method to study brain activity. In the previous decade the advantages of MEG -- good temporal resolution combined with good spatial resolution allowing separation of activated brain areas -- have been successfully used in gaining new information about the neonatal brain functioning. In this review, we discuss the findings from studies of spontaneous magnetoencephalogram and evoked responses to somatosensory, auditory, and visual stimulation. Our group has shown that stimulation of the upper limb in neonates evokes a response sequence reflecting activation of both primary (S(I)) and secondary somatosensory (S(II)) cortices. Like in mature brains, the earliest cortical response to median nerve stimulation reflects the arrival of afferent information to S(I). However, source modeling of the subsequent activation from S(I)suggests immature cortical functioning in neonates. Another feature typical for neonates is that the S(II)response is prominent in quiet sleep, unlike in adults in whom it diminishes in sleep. Interestingly, in very prematurely-born infants, we found alterations of the somatosensory responses at both group and individual levels. MEG provides a novel way to look at brain activity in neonates and can be used to increase knowledge of the development of brain processing and its disturbances.

Increasing the efficiency of neonatal MEG measurements by alternating auditory and tactile stimulation

OBJECTIVE

To evaluate the possible effect of intervening auditory stimulation on somatosensory evoked magnetic fields in newborns.

METHODS

We recorded auditory and tactile evoked responses with magnetoencephalography (MEG) from two groups of healthy newborns. One group (n=11) received only tactile stimuli to the index finger, the other (n=11) received alternating tactile and auditory (vowel [a:] with 300-ms duration) stimuli. The interval between subsequent tactile stimuli was always 2 s. We analyzed the equivalent current dipoles (ECDs) of the main auditory and somatosensory responses.

RESULTS

The ECDs of the tactile responses agreed with activation of the primary somatosensory cortex at ∼60 ms and the secondary somatosensory region at ∼200 ms. The source of the auditory response (∼250 ms) was clearly distinct from those to tactile stimulation and in line with auditory cortex activation. The intervening auditory stimulation did not affect the strength, latency, or location of the ECDs of the tactile responses.

CONCLUSIONS

Auditory and tactile MEG responses from newborns can be obtained in one measurement session.

SIGNIFICANCE

The alternating stimulation can be used to shorten the total measurement time and/or to improve the signal to noise ratio by collecting more data.