Sex differences associated with corpus callosum development in human infants: A longitudinal multimodal imaging study

White matter microstructure, traumatic brain injury, and disruptive behavior disorders in girls and boys

Introduction

Girls and boys presenting disruptive behavior disorders (DBDs) display differences in white matter microstructure (WMM) relative to typically developing (TD) sex-matched peers. Boys with DBDs are at increased risk for traumatic brain injuries (TBIs), which are also known to impact WMM. This study aimed to disentangle associations of WMM with DBDs and TBIs.

Methods

The sample included 673 children with DBDs and 836 TD children, aged 9-10, from the Adolescent Brain Cognitive Development Study. Thirteen white matter bundles previously associated with DBDs were the focus of study. Analyses were undertaken separately by sex, adjusting for callous-unemotional traits (CU), attention-deficit hyperactivity disorder (ADHD), age, pubertal stage, IQ, ethnicity, and family income.

Results

Among children without TBIs, those with DBDs showed sex-specific differences in WMM of several tracts relative to TD. Most differences were associated with ADHD, CU, or both. Greater proportions of girls and boys with DBDs than sex-matched TD children had sustained TBIs. Among girls and boys with DBDs, those who had sustained TBIs compared to those not injured, displayed WMM alterations that were robust to adjustment for all covariates. Across most DBD/TD comparisons, axonal density scores were higher among children presenting DBDs.

Discussion

In conclusion, in this community sample of children, those with DBDs were more likely to have sustained TBIs that were associated with additional, sex-specific, alterations of WMM. These additional alterations further compromise the future development of children with DBDs.

Insight into brain sex differences of typically developed infants and brain pathologies: A systematic review

The continually advancing landscape of neuroscientific and imaging research has broadened our comprehension of sex differences encoded in the human brain, expanding from the hypothalamus and sexual behaviour to encompass the entire brain, including its diverse lobes, structures, and functions. However, less is known about sex differences in the brains of neonates and infants, despite their relevance to various sex-linked diseases that develop early in life. In this review, we provide a synopsis of the literature evidence on sex differences in the brains of neonates and infants at the morphological, structural and network levels. We also briefly overview the present evidence on the sex bias in some brain disorders affecting infants and neonates.

Surface-based morphometry of the corpus callosum in young children of ages 1-5

The corpus callosum (CC) is a large white matter fiber bundle in the brain and is involved in various cognitive, sensory, and motor processes. While implicated in various developmental and psychiatric disorders, much is yet to be uncovered about the normal development of this structure, especially in young children. Additionally, while sexual dimorphism has been reported in prior literature, observations have not necessarily been consistent. In this study, we use morphometric measures including surface tensor-based morphometry (TBM) to investigate local changes in the shape of the CC in children between the ages of 12 and 60 months, in intervals of 12 months. We also analyze sex differences in each of these age groups. We observed larger significant clusters in the earlier ages between 12 v 24 m and between 48 v 60 m and localized differences in the anterior region of the body of the CC. Sex differences were most pronounced in the 12 m group. This study adds to the growing literature of work aiming to understand the developing brain and emphasizes the utility of surface TBM as a useful tool for analyzing regional differences in neuroanatomical morphometry.

The Role of Puberty and Sex on Brain Structure in Adolescents With Anxiety Following Concussion

BACKGROUND

Adolescence represents a window of vulnerability for developing psychological symptoms following concussion, especially in girls. Concussion-related lesions in emotion regulation circuits may help explain these symptoms. However, the contribution of sex and pubertal maturation remains unclear. Using the neurite density index (NDI) in emotion regulation tracts (left/right cingulum bundle [CB], forceps minor [FMIN], and left/right uncinate fasciculus), we sought to elucidate these relationships.

METHODS

No adolescent had a history of anxiety and/or depression. The Screen for Child Anxiety Related Emotional Disorders and Children's Depression Rating Scale were used at scan to assess anxiety and depressive symptoms in 55 concussed adolescents (41.8% girls) and 50 control adolescents with no current/history of concussion (44% girls). We evaluated if a mediation-moderation model including the NDI (mediation) and sex or pubertal status (moderation) could help explain this relationship.

RESULTS

Relative to control adolescents, concussed adolescents showed higher anxiety (p = .003) and lower NDI, with those at more advanced pubertal maturation showing greater abnormalities in 4 clusters: the left CB frontal (p = .002), right CB frontal (p = .011), FMIN left-sided (p = .003), and FMIN right-sided (p = .003). Across all concussed adolescents, lower NDI in the left CB frontal and FMIN left-sided clusters partially mediated the association between concussion and anxiety, with the CB being specific to female adolescents. These effects did not explain depressive symptoms.

CONCLUSIONS

Our findings indicate that lower NDI in the CB and FMIN may help explain anxiety following concussion and that adolescents at more advanced (vs less advanced) status of pubertal maturation may be more vulnerable to concussion-related injuries, especially in girls.

Insights into morphometry and topography of corpus callosum among Indians

Corpus callosum is one of the major association fibre of brain performs an integral role of integration and communication of information between the two hemispheres. 50 formalin fixed cerebral hemispheres (25 right and 25 left) were used for the study. The longitudinal and vertical length of brain, longitudinal length and height of corpus callosum, distance of corpus callosum from various landmarks such as frontal and occipital pole, anterior commissure, lamina terminalis, and highest point on parietal pole and width of different parts of corpus callosum and height were measured. Results were analysed statistically. The results showed positive correlation between the longitudinal dimension of brain and all other parameters. Morphometric variation in size and its relation to nearby structures are seen in many neurological and psychiatric conditions such as Alzheimer's disease, Schizophrenia and bipolar disorders. Hence the present study can be used as reference by neurologist, neurosurgeons and psychiatrists.

Exploring interhemispheric connectivity using the directional tract density patterns of the corpus callosum

The corpus callosum (CC) is one of the most important interhemispheric white matter tracts that connects interrelated regions of the cerebral cortex. Its disruption has been investigated in previous studies and has been found to play an important role in several neurodegenerative disorders. Currently available methods to assess the interhemispheric connectivity of the CC have several limitations: i) they require the a priori identification of specific cortical regions as targets or seeds, ii) they are limited by the characterization of only small components of the structure, primarily voxels that constitute the mid-sagittal slice, and iii) they use global measures of microstructural integrity, which provide only limited characterization. In order to address some of these limitations, we developed a novel method that enables the characterization of white matter tracts covering the structure of CC, from the mid-sagittal plane to corresponding regions of cortex, using directional tract density patterns (dTDPs). We demonstrate that different regions of CC have distinctive dTDPs that reflect a unique regional topology. We conducted a pilot study using this approach to evaluate two different datasets collected from healthy subjects, and we demonstrate that this method is reliable, reproducible, and independent of diffusion acquisition parameters, suggesting its potential applicability to clinical applications.

The genetic architecture of the corpus callosum and its genetic overlap with common neuropsychiatric diseases

BACKGROUND

The corpus callosum (CC) is the main structure transferring information between the cerebral hemispheres. Although previous large-scale genome-wide association study (GWAS) has illustrated the genetic architecture of white matter integrity of CC, CC volume is less stressed.

METHODS

Using MRI data from 33,861 individuals in UK Biobank, we conducted univariate and multivariate GWAS for CC fractional anisotropy (FA) and volume with PLINK 2.0 and MOSTest. All discovered SNPs in the multivariate framework were functionally annotated in FUMA v1.3.8. In the meanwhile, a series of gene property analyses was conducted simultaneously. In addition, we estimated genetic relationship between CC metrics and other neuropsychiatric traits and diseases.

RESULTS

We identified a total of 36 and 82 significant genomic loci for CC FA and volume (P < 5 × 10^-8). And 53 and 27 genes were respectively mapped by four mapping strategies. For CC volume, gene-set analysis revealed pathways mainly relating to cell migration; cell-type analysis found the top enrichment in neuroglia while for CC FA in GABAergic neurons. Furthermore, we found a lot of genetic overlap and shared loci between CC FA and volume and common neuropsychiatric diseases.

DISCUSSION

Collectively, this study helps to better understand the genetic architecture of whole CC and CC subregions. However, the way to divide CC FA and volume in our study restricts the interpretations of our results. Future work will be needed to pay attention to the genetic structure of white matter volume, and an appropriate division of CC may help to better understand CC structure.

Three dimensional development and asymmetry of the corpus callosum in the 0-18 age group: A retrospective magnetic resonance imaging study

Most of the corpus callosum (CC) developmental studies are concerned with its two-dimensional structure. Linear and area measurements do not directly assess the CC size but estimate the overall structure from the cross-sectional image. This study investigated age- and sex-related changes in volumetric development and asymmetry of CC from birth to 18. For this retrospective study, we selected 696 patients (329 [47.27%] females) with both 3D-T1-weighted sequence and normal radiological anatomy from patients 0-18 years of age who had brain magnetic resonance imaging (MRI) between 2012 and 2020. The genu, body, splenium, and total volume of CC were calculated using MRICloud. The measurement results of 23 age groups were analyzed with SPSS (ver.28). Total CC volume was 18740.76 ± 4314.06 mm³ between 0 and 18 years of age, and its ratio to total brain volume (TBV) was 1.70% ± 0.23%. We observed that the total CC volume has six developmental periods 0 years, 1, 2-4, 5-9, 10-16, and 17-18 years. Genu and body grew in five developmental periods, while splenium in seven. There was intermittent sexual dimorphism in the CC volume in the first 4 years of life (p < 0.05). However, sex factor was insignificant in CC ratio to TBV. Total CC was right lateralized on average 1.81% (ranging -0.59% to 4.52%). Genu was 8.70% lateralized to the right, the body was 2.99% to the left, and the splenium was 1.41% to the right. The three-dimensional development of CC agreed with the two-dimensional developmental data of CC except for some differences.

Sex differences in brain homotopic co-activations: a meta-analytic study

An element of great interest in functional connectivity is 'homotopic connectivity' (HC), namely the connectivity between two mirrored areas of the two hemispheres, mainly mediated by the fibers of the corpus callosum. Despite a long tradition of studying sexual dimorphism in the human brain, to our knowledge only one study has addressed the influence of sex on HC.We investigated the issue of homotopic co-activations in women and men using a coordinate-based meta-analytic method and data from the BrainMap database. A first unexpected observation was that the database was affected by a sex bias: women-only groups are investigated less often than men-only ones, and they are more often studied in certain domains such as emotion compared to men, and less in cognition. Implementing a series of sampling procedures to equalize the size and proportion of the datasets, our results indicated that females exhibit stronger interhemispheric co-activation than males, suggesting that the female brain is less lateralized and more integrated than that of males. In addition, males appear to show less intense but more extensive co-activation than females. Some local differences also appeared. In particular, it appears that primary motor and perceptual areas are more co-activated in males, in contrast to the opposite trend in the rest of the brain. This argues for a multidimensional view of sex brain differences and suggests that the issue should be approached with more complex models than previously thought.

Allometry in the corpus callosum in neonates: Sexual dimorphism

The corpus callosum (CC) is the largest fiber tract in the human brain, allowing interhemispheric communication by connecting homologous areas of the two cerebral hemispheres. In adults, CC size shows a robust allometric relationship with brain size, with larger brains having larger callosa, but smaller brains having larger callosa relative to brain size. Such an allometric relationship has been shown in both males and females, with no significant difference between the sexes. But there is some evidence that there are alterations in these allometric relationships during development. However, it is currently not known whether there is sexual dimorphism in these allometric relationships from birth, or if it only develops later. We study this in neonate data. Our results indicate that there are already sex differences in these allometric relationships in neonates: male neonates show the adult‐like allometric relationship between CC size and brain size; however female neonates show a significantly more positive allometry between CC size and brain size than either male neonates or female adults. The underlying cause of this sexual dimorphism is unclear; but the existence of this sexual dimorphism in neonates suggests that sex‐differences in lateralization have prenatal origins.

Individual variability in the nonlinear development of the corpus callosum during infancy and toddlerhood: a longitudinal MRI analysis

The human brain spends several years bootstrapping itself through intrinsic and extrinsic modulation, thus gradually developing both spatial organization and functions. Based on previous studies on developmental patterns and inter-individual variability of the corpus callosum (CC), we hypothesized that inherent variations of CC shape among infants emerge, depending on the position within the CC, along the developmental timeline. Here we used longitudinal magnetic resonance imaging data from infancy to toddlerhood and investigated the area, thickness, and shape of the midsagittal plane of the CC by applying multilevel modeling. The shape characteristics were extracted using the Procrustes method. We found nonlinearity, region-dependency, and inter-individual variability, as well as intra-individual consistencies, in CC development. Overall, the growth rate is faster in the first year than in the second year, and the trajectory differs between infants; the direction of CC formation in individual infants was determined within six months and maintained to two years. The anterior and posterior subregions increase in area and thickness faster than other subregions. Moreover, we clarified that the growth rate of the middle part of the CC is faster in the second year than in the first year in some individuals. Since the division of regions exhibiting different tendencies coincides with previously reported divisions based on the diameter of axons that make up the region, our results suggest that subregion-dependent individual variability occurs due to the increase in the diameter of the axon caliber, myelination partly due to experience and axon elimination during the early developmental period.

Corpus Callosum Volumes in Children with Autism Spectrum Disorders: Sex-Associated Differences

This study aimed to analyze the relationship between sex and corpus callosum (CC) volume in children with autism spectrum disorders (ASD) aged 2-4 years. This prospective study included 50 children with ASD and 50 typically developing (TD) children aged 2-4 years. Midsagittal slices of the CCs of the participants were divided into five subregions using FreeSurfer software. The PMCC, AMCC and TCC volumes were significantly higher in ASD participants than in TD participants, and results were significant in females with ASD rather than in males with ASD (all P < 0.05). In toddlers with ASD, the CC volumes were increased and more pronounced in females than in males. This could be due to overgrowth of axons or/and axonal pruning disorders.

Infant and Child MRI: A Review of Scanning Procedures

Magnetic resonance imaging (MRI) is a safe method to examine human brain. However, a typical MR scan is very sensitive to motion, and it requires the subject to lie still during the acquisition, which is a major challenge for pediatric scans. Consequently, in a clinical setting, sedation or general anesthesia is often used. In the research setting including healthy subjects anesthetics are not recommended for ethical reasons and potential longer-term harm. Here we review the methods used to prepare a child for an MRI scan, but also on the techniques and tools used during the scanning to enable a successful scan. Additionally, we critically evaluate how studies have reported the scanning procedure and success of scanning. We searched articles based on special subject headings from PubMed and identified 86 studies using brain MRI in healthy subjects between 0 and 6 years of age. Scan preparations expectedly depended on subject's age; infants and young children were scanned asleep after feeding and swaddling and older children were scanned awake. Comparing the efficiency of different procedures was difficult because of the heterogeneous reporting of the used methods and the success rates. Based on this review, we recommend more detailed reporting of scanning procedure to help find out which are the factors affecting the success of scanning. In the long term, this could help the research field to get high quality data, but also the clinical field to reduce the use of anesthetics. Finally, we introduce the protocol used in scanning 2 to 5-week-old infants in the FinnBrain Birth Cohort Study, and tips for calming neonates during the scans.

Cerebral White Matter Myelination and Relations to Age, Gender, and Cognition: A Selective Review

White matter makes up about fifty percent of the human brain. Maturation of white matter accompanies biological development and undergoes the most dramatic changes during childhood and adolescence. Despite the advances in neuroimaging techniques, controversy concerning spatial, and temporal patterns of myelination, as well as the degree to which the microstructural characteristics of white matter can vary in a healthy brain as a function of age, gender and cognitive abilities still exists. In a selective review we describe methods of assessing myelination and evaluate effects of age and gender in nine major fiber tracts, highlighting their role in higher-order cognitive functions. Our findings suggests that myelination indices vary by age, fiber tract, and hemisphere. Effects of gender were also identified, although some attribute differences to methodological factors or social and learning opportunities. Findings point to further directions of research that will improve our understanding of the complex myelination-behavior relation across development that may have implications for educational and clinical practice.

Prenatal antidepressant exposure and sex differences in neonatal corpus callosum microstructure

Prenatal exposure to selective serotonin reuptake inhibitor (SSRI) antidepressants may influence white matter (WM) development, as previous studies report widespread microstructural alterations and reduced interhemispheric connectivity in SSRI-exposed infants. In rodents, perinatal SSRIs had sex-specific disruptions in corpus callosum (CC) axon architecture and connectivity; yet it is unknown whether SSRI-related brain outcomes in humans are sex specific. In this study, the neonate CC was selected as a region-of-interest to investigate whether prenatal SSRI exposure has sex-specific effects on early WM microstructure. On postnatal day 7, diffusion tensor imaging was used to assess WM microstructure in SSRI-exposed (n = 24; 12 male) and nonexposed (n = 48; 28 male) term-born neonates. Fractional anisotropy was extracted from CC voxels and a multivariate discriminant analysis was used to identify latent patterns differing between neonates grouped by SSRI-exposure and sex. Analysis revealed localized variations in CC fractional anisotropy that significantly discriminated neonate groups and correctly predicted group membership with an 82% accuracy. Such effects were identified across three dimensions, representing sex differences in SSRI-exposed neonates (genu, splenium), SSRI-related effects independent of sex (genu-to-rostral body), and sex differences in nonexposed neonates (isthmus-splenium, posterior midbody). Our findings suggest that CC microstructure may have a sex-specific, localized, developmental sensitivity to prenatal SSRI exposure.