Functional connectivity for the language network in the developing brain: 30 weeks of gestation to 30 months of age.

Although the neural scaffolding for language is putatively present before birth, the maturation of functional connections among the key nodes of the language network, Broca's and Wernicke's areas, is less known. We leveraged longitudinal and cross-sectional data from three sites collected through six studies to track the development of functional circuits between Broca's and Wernicke's areas from 30 weeks of gestation through 30 months of age in 127 unique participants. Using resting-state fMRI data, functional connectivity was calculated as the correlation between fMRI time courses from pairs of regions, defined as Broca's and Wernicke's in both hemispheres. The primary analysis evaluated 23 individuals longitudinally imaged from 30 weeks postmenstrual age (fetal) through the first postnatal month (neonatal). A secondary analysis in 127 individuals extended these curves into older infants and toddlers. These data demonstrated significant growth of interhemispheric connections including left Broca's and its homolog and left Wernicke's and its homolog from 30 weeks of gestation through the first postnatal month. In contrast, intrahemispheric connections did not show significant increases across this period. These data represent an important baseline for language systems in the developing brain against which to compare those neurobehavioral disorders with the potential fetal onset of disease.

SMC5 Plays Independent Roles in Congenital Heart Disease and Neurodevelopmental Disability.

Up to 50% of patients with severe congenital heart disease (CHD) develop life-altering neurodevelopmental disability (NDD). It has been presumed that NDD arises in CHD cases because of hypoxia before, during, or after cardiac surgery. Recent studies detected an enrichment in de novo mutations in CHD and NDD, as well as significant overlap between CHD and NDD candidate genes. However, there is limited evidence demonstrating that genes causing CHD can produce NDD independent of hypoxia. A patient with hypoplastic left heart syndrome and gross motor delay presented with a de novo mutation in SMC5. Modeling mutation of smc5 in Xenopus tropicalis embryos resulted in reduced heart size, decreased brain length, and disrupted pax6 patterning. To evaluate the cardiac development, we induced the conditional knockout (cKO) of Smc5 in mouse cardiomyocytes, which led to the depletion of mature cardiomyocytes and abnormal contractility. To test a role for Smc5 specifically in the brain, we induced cKO in the mouse central nervous system, which resulted in decreased brain volume, and diminished connectivity between areas related to motor function but did not affect vascular or brain ventricular volume. We propose that genetic factors, rather than hypoxia alone, can contribute when NDD and CHD cases occur concurrently.

Age-related topographic map of magnetic resonance diffusion metrics in neonatal brains.

Accelerated maturation of brain parenchyma close to term-equivalent age leads to rapid changes in diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) metrics of neonatal brains, which can complicate the evaluation and interpretation of these scans. In this study, we characterized the topography of age-related evolution of diffusion metrics in neonatal brains. We included 565 neonates who had MRI between 0 and 3 months of age, with no structural or signal abnormality-including 162 who had DTI scans. We analyzed the age-related changes of apparent diffusion coefficient (ADC) values throughout brain and DTI metrics (fractional anisotropy [FA] and mean diffusivity [MD]) along white matter (WM) tracts. Rate of change in ADC, FA, and MD values across 5 mm cubic voxels was calculated. There was significant reduction of ADC and MD values and increase of FA with increasing gestational age (GA) throughout neonates' brain, with the highest temporal rates in subcortical WM, corticospinal tract, cerebellar WM, and vermis. GA at birth had significant effect on ADC values in convexity cortex and corpus callosum as well as FA/MD values in corpus callosum, after correcting for GA at scan. We developed online interactive atlases depicting age-specific normative values of ADC (ages 34-46 weeks), and FA/MD (35-41 weeks). Our results show a rapid decrease in diffusivity metrics of cerebral/cerebellar WM and vermis in the first few weeks of neonatal age, likely attributable to myelination. In addition, prematurity and low GA at birth may result in lasting delay in corpus callosum myelination and cerebral cortex cellularity.

Fine Motor Skill Mediates Visual Memory Ability with Microstructural Neuro-correlates in Cerebellar Peduncles in Prematurely Born Adolescents.

Adolescents born preterm (PT) with no evidence of neonatal brain injury are at risk of deficits in visual memory and fine motor skills that diminish academic performance. The association between these deficits and white matter microstructure is relatively unexplored. We studied 190 PTs with no brain injury and 92 term controls at age 16 years. The Rey-Osterrieth Complex Figure Test (ROCF), the Beery visual-motor integration (VMI), and the Grooved Pegboard Test (GPT) were collected for all participants, while a subset (40 PTs and 40 terms) underwent diffusion-weighted magnetic resonance imaging. PTs performed more poorly than terms on ROCF, VMI, and GPT (all P < 0.01). Mediation analysis showed fine motor skill (GPT score) significantly mediates group difference in ROCF and VMI (all P < 0.001). PTs showed a negative correlation (P < 0.05, corrected) between fractional anisotropy (FA) in the bilateral middle cerebellar peduncles and GPT score, with higher FA correlating to lower (faster task completion) GPT scores, and between FA in the right superior cerebellar peduncle and ROCF scores. PTs also had a positive correlation (P < 0.05, corrected) between VMI and left middle cerebellar peduncle FA. Novel strategies to target fine motor skills and the cerebellum may help PTs reach their full academic potential.

Alterations in Anatomical Covariance in the Prematurely Born.

Preterm (PT) birth results in long-term alterations in functional and structural connectivity, but the related changes in anatomical covariance are just beginning to be explored. To test the hypothesis that PT birth alters patterns of anatomical covariance, we investigated brain volumes of 25 PTs and 22 terms at young adulthood using magnetic resonance imaging. Using regional volumetrics, seed-based analyses, and whole brain graphs, we show that PT birth is associated with reduced volume in bilateral temporal and inferior frontal lobes, left caudate, left fusiform, and posterior cingulate for prematurely born subjects at young adulthood. Seed-based analyses demonstrate altered patterns of anatomical covariance for PTs compared with terms. PTs exhibit reduced covariance with R Brodmann area (BA) 47, Broca's area, and L BA 21, Wernicke's area, and white matter volume in the left prefrontal lobe, but increased covariance with R BA 47 and left cerebellum. Graph theory analyses demonstrate that measures of network complexity are significantly less robust in PTs compared with term controls. Volumes in regions showing group differences are significantly correlated with phonological awareness, the fundamental basis for reading acquisition, for the PTs. These data suggest both long-lasting and clinically significant alterations in the covariance in the PTs at young adulthood.

Does prenatal stress alter the developing connectome?

Human neurodevelopment requires the organization of neural elements into complex structural and functional networks called the connectome. Emerging data suggest that prenatal exposure to maternal stress plays a role in the wiring, or miswiring, of the developing connectome. Stress-related symptoms are common in women during pregnancy and are risk factors for neurobehavioral disorders ranging from autism spectrum disorder, attention deficit hyperactivity disorder, and addiction, to major depression and schizophrenia. This review focuses on structural and functional connectivity imaging to assess the impact of changes in women's stress-based physiology on the dynamic development of the human connectome in the fetal brain.

Cerebral Lateralization is Protective in the Very Prematurely Born.

Individuals born prematurely are at risk for developmental delay, and converging data suggest alterations in neural networks in the developing preterm brain. Nevertheless, those critical period processes such as cerebral lateralization that underlie these findings remain largely unexplored. To test the hypothesis that preterm birth alters the fundamental program of corticogenesis in the developing brain, we interrogated cerebral lateralization at rest in very prematurely born participants and term controls at young adulthood. Employing a novel, voxel-based measure of functional connectivity, these data demonstrate for the first time that cerebral lateralization of functional connectivity in right hemisphere language homologs is altered for very preterm participants. Very preterm participants with no evidence for severe brain injury exhibited a significant decrease in right hemisphere lateralization in the right parietal and temporal lobes in this data driven analysis. Further, for the very preterm participants, but not the term participants, these fundamental alterations in the cerebral lateralization for language significantly correlate with language scores. These findings provide evidence that cerebral asymmetry is both plastic and experiential, and suggest the need for further study of underlying environmental factors responsible for these changes.

Functional magnetic resonance connectivity studies in infants born preterm: suggestions of proximate and long-lasting changes in language organization.

Sophisticated neuroimaging strategies demonstrate alterations in functional connectivity at school age, adolescence, and young adulthood in individuals born preterm. Recent data suggest these alterations are present in the postnatal period prior to term-equivalent age in neonates born preterm. Likewise, functional organization increases across development, but the influence of preterm birth on this fundamental infrastructure is immediate and unchanging. This article briefly reviews the current methods of measuring functional connectivity throughout development in those born preterm, and the association of functional connectivity with language disorders. Taken together, these data suggest that the effects of preterm birth on the functional organization of language in the developing brain are both proximate and long-lasting.

Adaptive mechanisms of developing brain: cerebral lateralization in the prematurely-born.

Preterm birth results in alterations in neural connectivity, but the impact of prematurity on the functional organization of the developing brain has yet to be explored. To test the hypothesis that preterm birth alters cortical organization during the late second and third trimesters of gestation, we interrogated cerebral lateralization at rest in 26 very preterm subjects (birth weight 500-1500g) with no evidence of brain injury and 25 healthy term control subjects at term equivalent age. Employing an unbiased voxel-based measure of functional connectivity, these data demonstrated that cerebral lateralization is impaired in the prematurely-born. At term equivalent age, preterm neonates showed significantly less lateralization in regions subserving both receptive and expressive language, left Brodmann (BA) areas insula-BA22-BA21 and L BA45-BA47 (p<0.05 corrected for multiple comparisons for both). Exploratory region of interest analyses demonstrated significantly less inter-hemispheric connectivity from L BA22 to R BA22 in preterm infants compared to term controls (p<0.005) and from R BA22 to its homolog (p<0.005). L BA22, Wernicke's area, was more strongly connected to R BA39, foreshadowing neural networks for language in preterm subjects at school age, adolescence and young adulthood. For these very preterm neonates born at less than 30weeks' PMA, the degree of prematurity had no influence on lateralization in these differential regions.

Maternal race, demography, and health care disparities impact risk for intraventricular hemorrhage in preterm neonates.

OBJECTIVE: To determine whether risk factors associated with grade 2-4 intraventricular hemorrhage (IVH) differs between infants of African ancestry and white infants. STUDY DESIGN: Inborn, appropriate for gestational age infants with birth weight 500-1250 g and exposure to at least 1 dose of antenatal steroids were enrolled in 24 neonatal intensive care units. Cases had grade 2-4 IVH and controls matched for site, race, and birth weight range had 2 normal ultrasounds read centrally. Multivariate logistic regression modeling identified factors associated with IVH across African ancestry and white race. RESULTS: Subjects included 579 African ancestry or white race infants with grade 2-4 IVH and 532 controls. Mothers of African ancestry children were less educated, and white case mothers were more likely to have more than 1 prenatal visit and multiple gestation (P ≤ .01 for all). Increasing gestational age (P = .01), preeclampsia (P < .001), complete antenatal steroid exposure (P = .02), cesarean delivery (P < .001), and white race (P = .01) were associated with decreased risk for IVH. Chorioamnionitis (P = .01), 5-minute Apgar score <3 (P < .004), surfactant use (P < .001), and high-frequency ventilation (P < .001) were associated with increased risk for IVH. Among African ancestry infants, having more than 1 prenatal visit was associated with decreased risk (P = .02). Among white infants, multiple gestation was associated with increased risk (P < .001), and higher maternal education was associated with decreased risk (P < .05). CONCLUSION: The risk for IVH differs between infants of African ancestry and white infants, possibly attributable to both race and health care disparities.

Gene-environment interactions in severe intraventricular hemorrhage of preterm neonates.

Intraventricular hemorrhage (IVH) of the preterm neonate is a complex developmental disorder, with contributions from both the environment and the genome. IVH, or hemorrhage into the germinal matrix of the developing brain with secondary periventricular infarction, occurs in that critical period of time before the 32nd to 33rd wk postconception and has been attributed to changes in cerebral blood flow to the immature germinal matrix microvasculature. Emerging data suggest that genes subserving coagulation, inflammatory, and vascular pathways and their interactions with environmental triggers may influence both the incidence and severity of cerebral injury and are the subject of this review. Polymorphisms in the Factor V Leiden gene are associated with the atypical timing of IVH, suggesting an as yet unknown environmental trigger. The methylenetetrahydrofolate reductase (MTHFR) variants render neonates more vulnerable to cerebral injury in the presence of perinatal hypoxia. The present study demonstrates that the MTHFR 677C>T polymorphism and low 5-min Apgar score additively increase the risk of IVH. Finally, review of published preclinical data suggests the stressors of delivery result in hemorrhage in the presence of mutations in collagen 4A1, a major structural protein of the developing cerebral vasculature. Maternal genetics and fetal environment may also play a role.

Adolescents born prematurely with isolated grade 2 haemorrhage in the early 1990s face increased risks of learning challenges.

AIM: To compare the impact of low-grade haemorrhage on neurocognitive function in 16-year-old adolescents born preterm, by grade of intraventricular haemorrhage, and term controls. METHODS: We evaluated 338 preterm adolescents (birth weight 600-1250 g) for intelligence, executive function and memory tasks. Eleven had grade 3-4 haemorrhage, 44 had grade 2, 31 had grade 1, and 251 had no haemorrhage. Group comparisons were made with 102 term age-matched controls, and regression models used to identify the risk that low-grade haemorrhage posed for cognitive, executive function and memory deficits. RESULTS: Preterm adolescents with grade 2 haemorrhage had higher deficit rates of verbal intelligence, receptive vocabulary, phonemic fluency, cognitive flexibility and phonological fluency than preterm adolescents with grade 1 or no haemorrhage, compared with term controls. After excluding preterm adolescents with both grade 2 haemorrhage and cystic periventricular leukomalacia, those with isolated grade 2 haemorrhage remained at greater risk of cognitive and executive function deficits than term controls and of cognitive deficits than preterm adolescents with no haemorrhage. CONCLUSION: Our findings suggest that preterm adolescents born in the early 1990s with isolated grade 2 haemorrhage are at increased risk of learning challenges, including cognitive and executive function deficits.

Environmental enrichment increases the GFAP+ stem cell pool and reverses hypoxia-induced cognitive deficits in juvenile mice.

Premature children born with very low birth weight (VLBW) can suffer chronic hypoxic injury as a consequence of abnormal lung development and cardiovascular abnormalities, often leading to grave neurological and behavioral consequences. Emerging evidence suggests that environmental enrichment improves outcome in animal models of adult brain injury and disease; however, little is known about the impact of environmental enrichment following developmental brain injury. Intriguingly, data on socio-demographic factors from longitudinal studies that examined a number of VLBW cohorts suggest that early environment has a substantial impact on neurological and behavioral outcomes. In the current study, we demonstrate that environmental enrichment significantly enhances behavioral and neurobiological recovery from perinatal hypoxic injury. Using a genetic fate-mapping model that allows us to trace the progeny of GFAP+ astroglial cells, we show that hypoxic injury increases the proportion of astroglial cells that attain a neuronal fate. In contrast, environmental enrichment increases the stem cell pool, both through increased stem cell proliferation and stem cell survival. In mice subjected to hypoxia and subsequent enrichment there is an additive effect of both conditions on hippocampal neurogenesis from astroglia, resulting in a robust increase in the number of neurons arising from GFAP+ cells by the time these mice reach full adulthood.

A left cerebellar pathway mediates language in prematurely-born young adults.

Preterm (PT) subjects are at risk for developmental delay, and task-based studies suggest that developmental disorders may be due to alterations in neural connectivity. Since emerging data imply the importance of right cerebellar function for language acquisition in typical development, we hypothesized that PT subjects would have alternate areas of cerebellar connectivity, and that these areas would be responsible for differences in cognitive outcomes between PT subjects and term controls at age 20 years. Nineteen PT and 19 term control young adults were prospectively studied using resting-state functional MRI (fMRI) to create voxel-based contrast maps reflecting the functional connectivity of each tissue element in the grey matter through analysis of the intrinsic connectivity contrast degree (ICC-d). Left cerebellar ICC-d differences between subjects identified a region of interest that was used for subsequent seed-based connectivity analyses. Subjects underwent standardized language testing, and correlations with cognitive outcomes were assessed. There were no differences in gender, hand preference, maternal education, age at study, or Peabody Picture Vocabulary Test (PPVT) scores. Functional connectivity (FcMRI) demonstrated increased tissue connectivity in the biventer, simple and quadrangular lobules of the L cerebellum (p<0.05) in PTs compared to term controls; seed-based analyses from these regions demonstrated alterations in connectivity from L cerebellum to both R and L inferior frontal gyri (IFG) in PTs compared to term controls. For PTs but not term controls, there were significant positive correlations between these connections and PPVT scores (R IFG: r=0.555, p=0.01; L IFG: r=0.454, p=0.05), as well as Verbal Comprehension Index (VCI) scores (R IFG: r=0.472, p=0.04). These data suggest the presence of a left cerebellar language circuit in PT subjects at young adulthood. These findings may represent either a delay in maturation or the engagement of alternative neural pathways for language in the developing PT brain.

Candidate gene analysis: severe intraventricular hemorrhage in inborn preterm neonates.

Intraventricular hemorrhage (IVH) is a disorder of complex etiology. We analyzed genotypes for 7 genes from 224 inborn preterm neonates treated with antenatal steroids and grade 3-4 IVH and 389 matched controls. Only methylenetetrahydrofolate reductase was more prevalent in cases of IVH, emphasizing the need for more comprehensive genetic strategies.

Brain injury patterns in hypoxic ischemic encephalopathy of term neonates.

BACKGROUND AND PURPOSE: Topographic patterns of brain injury in neonates can help with differentiation and prognostic categorization of hypoxic ischemic encephalopathy (HIE). In this study, we quantitatively and objectively characterized the location of hypoxic ischemic lesions in term neonates with varying severity of HIE. METHODS: We analyzed term neonates (born ≥37 postmenstrual gestational weeks) with MRI diffusion-weighted imaging (DWI) and diagnoses of HIE. Neonates' HIE was categorized into mild, moderate, and severe. The hypoxic ischemic lesions were segmented on DWI series with attention to T1- and T2-weighted images and then co-registered onto standard brain space to generate summation maps for each severity category. Applying voxel-wise general linear models, we also identified cerebral regions more likely to infarct with increasing severity of HIE, after correction for lesion volume and time-to-scan as covariates. RESULTS: We included 33 neonates: 20 with mild, eight with moderate, and five with severe HIE. Infarct volumes (p = .00052) and Appearance, Pulse, Grimace, Activity, and Respiration scores at 1 minute (p = .032) differed between HIE severity categories. Hypoxic ischemic lesions in neonates with mild and moderate HIE were predominant in subcortical and deep white matter along the border zones of arterial supply territories, while severe HIE also involved basal ganglia, hippocampus, and thalamus. In voxel-wise analysis, higher severity of HIE was associated with the presence of lesions in hippocampus, thalamus, and lentiform nucleus. CONCLUSIONS: In term neonates, mild/moderate HIE is associated with infarctions of arterial territory watershed zones, whereas severe HIE distinctively involves basal ganglia, thalami, and hippocampi.

Early brain microstructural development among preterm infants requiring caesarean section versus those delivered vaginally.

It is known that the rate of caesarean section (C-section) has been increasing among preterm births. However, the relationship between C-section and long-term neurological outcomes is unclear. In this study, we utilized diffusion tensor imaging (DTI) to characterize the association of delivery method with brain white matter (WM) microstructural integrity in preterm infants. We retrospectively analyzed the DTI scans and health records of preterm infants without neuroimaging abnormality on pre-discharge term-equivalent MRI. We applied both voxel-wise and tract-based analyses to evaluate the association between delivery method and DTI metrics across WM tracts while controlling for numerous covariates. We included 68 preterm infants in this study (23 delivered vaginally, 45 delivered via C-section). Voxel-wise and tract-based analyses revealed significantly lower fractional anisotropy values and significantly higher diffusivity values across major WM tracts in preterm infants delivered via C-section when compared to those delivered vaginally. These results may be partially, but not entirely, mediated by lower birth weight among infants delivered by C-section. Nevertheless, these infants may be at risk for delayed neurodevelopment and could benefit from close neurological follow up for early intervention and mitigation of adverse long-term outcomes.