Diffusion Tensor Tractography of the Cerebellar Peduncles in Prematurely Born 7-Year-Old Children

Structural connectivity at term equivalent age and language in preterm children at 2 years corrected

We previously reported interhemispheric structural hyperconnectivity bypassing the corpus callosum in children born extremely preterm (<28 weeks) versus term children. This increased connectivity was positively associated with language performance at 4-6 years of age in our prior work. In the present study, we aim to investigate whether this extracallosal connectivity develops in extremely preterm infants at term equivalent age by leveraging a prospective cohort study of 350 very and extremely preterm infants followed longitudinally in the Cincinnati Infant Neurodevelopment Early Prediction Study. For this secondary analysis, we included only children born extremely preterm and without significant brain injury (n = 95). We use higher-order diffusion modelling to assess the degree to which extracallosal pathways are present in extremely preterm infants and predictive of later language scores at 22-26 months corrected age. We compare results obtained from two higher-order diffusion models: generalized q-sampling imaging and constrained spherical deconvolution. Advanced MRI was obtained at term equivalent age (39-44 weeks post-menstrual age). For structural connectometry analysis, we assessed the level of correlation between white matter connectivity at the whole-brain level at term equivalent age and language scores at 2 years corrected age, controlling for post-menstrual age, sex, brain abnormality score and social risk. For our constrained spherical deconvolution analyses, we performed connectivity-based fixel enhancement, using probabilistic tractography to inform statistical testing of the hypothesis that fibre metrics at term equivalent age relate to language scores at 2 years corrected age after adjusting for covariates. Ninety-five infants were extremely preterm with no significant brain injury. Of these, 53 had complete neurodevelopmental and imaging data sets that passed quality control. In the connectometry analyses adjusted for covariates and multiple comparisons (P < 0.05), the following tracks were inversely correlated with language: bilateral cerebellar white matter and middle cerebellar peduncles, bilateral corticospinal tracks, posterior commissure and the posterior inferior fronto-occipital fasciculus. No tracks from the constrained spherical deconvolution/connectivity-based fixel enhancement analyses remained significant after correction for multiple comparisons. Our findings provide critical information about the ontogeny of structural brain networks supporting language in extremely preterm children. Greater connectivity in more posterior tracks that include the cerebellum and connections to the regions of the temporal lobes at term equivalent age appears to be disadvantageous for language development.

An Animal Model of Neonatal Intensive Care Unit Exposure to Light and Sound in the Preterm Infant

According to the World Health Organization, ∼15 million children are born prematurely each year. Many of these infants end up spending days to weeks in a neonatal intensive care unit (NICU). Infants who are born prematurely are often exposed to noise and light levels that affect their auditory and visual development. Children often have long-term impairments in cognition, visuospatial processing, hearing, and language. We have developed a rodent model of NICU exposure to light and sound using the Mongolian gerbil (Meriones unguiculatus), which has a low-frequency human-like audiogram and is altricial. To simulate preterm infancy, the eyes and ears were opened prematurely, and animals were exposed to the NICU-like sensory environment throughout the gerbil's cortical critical period of auditory development. After the animals matured into adults, auditory perceptual testing was carried out followed by auditory brainstem response recordings and then histology to assess the white matter morphology of various brain regions. Compared to normal hearing control animals, NICU sensory-exposed animals had significant impairments in learning at later stages of training, increased auditory thresholds reflecting hearing loss, and smaller cerebellar white matter volumes. These have all been reported in longitudinal studies of preterm infants. These preliminary results suggest that this animal model could provide researchers with an ethical way to explore the effects of the sensory environment in the NICU on the preterm infant's brain development.

A unique cerebellar pattern of microglia activation in a mouse model of encephalopathy of prematurity

Preterm infants often show pathologies of the cerebellum, which are associated with impaired motor performance, lower IQ and poor language skills at school ages. Using a mouse model of inflammation-induced encephalopathy of prematurity driven by systemic administration of pro-inflammatory IL-1β, we sought to uncover causes of cerebellar damage. In this model, IL-1β is administered between postnatal day (P) 1 to day 5, a timing equivalent to the last trimester for brain development in humans. Structural MRI analysis revealed that systemic IL-1β treatment induced specific reductions in gray and white matter volumes of the mouse cerebellar lobules I and II (5% false discovery rate [FDR]) from P15 onwards. Preceding these MRI-detectable cerebellar volume changes, we observed damage to oligodendroglia, with reduced proliferation of OLIG2+ cells at P10 and reduced levels of the myelin proteins myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) at P10 and P15. Increased density of IBA1+ cerebellar microglia were observed both at P5 and P45, with evidence for increased microglial proliferation at P5 and P10. Comparison of the transcriptome of microglia isolated from P5 cerebellums and cerebrums revealed significant enrichment of pro-inflammatory markers in microglia from both regions, but cerebellar microglia displayed a unique type I interferon signaling dysregulation. Collectively, these data suggest that perinatal inflammation driven by systemic IL-1β leads to specific cerebellar volume deficits, which likely reflect oligodendrocyte pathology downstream of microglial activation. Further studies are now required to confirm the potential of protective strategies aimed at preventing sustained type I interferon signaling driven by cerebellar microglia as an important therapeutic target.

Quantitative mapping of the brain's structural connectivity using diffusion MRI tractography: A review

Diffusion magnetic resonance imaging (dMRI) tractography is an advanced imaging technique that enables in vivo reconstruction of the brain's white matter connections at macro scale. It provides an important tool for quantitative mapping of the brain's structural connectivity using measures of connectivity or tissue microstructure. Over the last two decades, the study of brain connectivity using dMRI tractography has played a prominent role in the neuroimaging research landscape. In this paper, we provide a high-level overview of how tractography is used to enable quantitative analysis of the brain's structural connectivity in health and disease. We focus on two types of quantitative analyses of tractography, including: 1) tract-specific analysis that refers to research that is typically hypothesis-driven and studies particular anatomical fiber tracts, and 2) connectome-based analysis that refers to research that is more data-driven and generally studies the structural connectivity of the entire brain. We first provide a review of methodology involved in three main processing steps that are common across most approaches for quantitative analysis of tractography, including methods for tractography correction, segmentation and quantification. For each step, we aim to describe methodological choices, their popularity, and potential pros and cons. We then review studies that have used quantitative tractography approaches to study the brain's white matter, focusing on applications in neurodevelopment, aging, neurological disorders, mental disorders, and neurosurgery. We conclude that, while there have been considerable advancements in methodological technologies and breadth of applications, there nevertheless remains no consensus about the "best" methodology in quantitative analysis of tractography, and researchers should remain cautious when interpreting results in research and clinical applications.

Neurobiological and behavioural outcomes of biofeedback-based training in autism: a randomized controlled trial

The human brain has demonstrated the power to structurally change as a result of movement-based interventions. However, it is unclear whether these structural brain changes differ in autistic individuals compared to non-autistic individuals. The purpose of the present study was to pilot a randomized controlled trial to investigate brain, balance, autism symptom severity and daily living skill changes that result from a biofeedback-based balance intervention in autistic adolescents (13-17 years old). Thirty-four autistic participants and 28 age-matched non-autistic participants underwent diagnostic testing and pre-training assessment (neuroimaging, cognitive, autism symptom severity and motor assessments) and were then randomly assigned to 6 weeks of a balance-training intervention or a sedentary-control condition. After the 6 weeks, neuroimaging, symptom severity and motor assessments were repeated. Results found that both the autistic and non-autistic participants demonstrated similar and significant increases in balance times with training. Furthermore, individuals in the balance-training condition showed significantly greater improvements in postural sway and reductions in autism symptom severity compared to individuals in the control condition. Daily living scores did not change with training, nor did we observe hypothesized changes to the microstructural properties of the corticospinal tract. However, follow-up voxel-based analyses found a wide range of balance-related structures that showed changes across the brain. Many of these brain changes were specific to the autistic participants compared to the non-autistic participants, suggesting distinct structural neuroplasticity in response to balance training in autistic participants. Altogether, these findings suggest that biofeedback-based balance training may target postural stability challenges, reduce core autism symptoms and influence neurobiological change. Future research is encouraged to examine the superior cerebellar peduncle in response to balance training and symptom severity changes in autistic individuals, as the current study produced overlapping findings in this brain region.

Tract-Specific Relationships Between Cerebrospinal Fluid Biomarkers and Periventricular White Matter in Posthemorrhagic Hydrocephalus of Prematurity

BACKGROUND

Posthemorrhagic hydrocephalus (PHH) is associated with neurological morbidity and complex neurosurgical care. Improved tools are needed to optimize treatments and to investigate the developmental sequelae of PHH.

OBJECTIVE

To examine the relationship between diffusion magnetic resonance imaging (dMRI) and cerebrospinal fluid (CSF) biomarkers of PHH.

METHODS

A total of 14 preterm (PT) infants with PHH and 46 controls were included. PT CSF was collected at temporizing surgery in PHH infants (PHH PT CSF) or lumbar puncture in controls. Term-equivalent age (TEA) CSF was acquired via implanted device or at permanent CSF diversion surgery in PHH (PHH-TEA-CSF) or lumbar puncture in controls. TEA dMRI scans were used to measure fractional anisotropy (FA) and mean diffusivity (MD) in the genu of corpus callosum (gCC), posterior limb of internal capsule (PLIC), and optic radiations (OPRA). Associations between dMRI measures and CSF amyloid precursor protein (APP), neural cell adhesion-1 (NCAM-1), and L1 cell adhesion molecule (L1CAM) were assessed using Pearson correlations.

RESULTS

APP, NCAM-1, and L1CAM were elevated over controls in PHH-PT-CSF and PHH-TEA-CSF. dMRI FA and MD differed between control and PHH infants across all tracts. PHH-PT-CSF APP levels correlated with gCC and OPRA FA and PLIC MD, while L1CAM correlated with gCC and OPRA FA. In PHH-TEA-CSF, only L1CAM correlated with OPRA MD.

CONCLUSION

Tract-specific associations were observed between dMRI and CSF biomarkers at the initiation of PHH treatment. dMRI and CSF biomarker analyses provide innovative complementary methods for examining PHH-related white matter injury and associated developmental sequelae.

Tractography of the Cerebellar Peduncles in Second- and Third-Trimester Fetuses

BACKGROUND AND PURPOSE

Little is known about microstructural development of cerebellar white matter in vivo. This study aimed to investigate developmental changes of the cerebellar peduncles in second- and third-trimester healthy fetuses using motion-corrected DTI and tractography.

MATERIALS AND METHODS

3T data of 81 healthy fetuses were reviewed. Structural imaging consisted of multiplanar T2-single-shot sequences; DTI consisted of a series of 12-direction diffusion. A robust motion-tracked section-to-volume registration algorithm reconstructed images. ROI-based deterministic tractography was performed using anatomic landmarks described in postnatal tractography. Asymmetry was evaluated qualitatively with a perceived difference of >25% between sides. Linear regression evaluated gestational age as a predictor of tract volume, ADC, and fractional anisotropy.

RESULTS

Twenty-four cases were excluded due to low-quality reconstructions. Fifty-eight fetuses with a median gestational age of 30.6 weeks (interquartile range, 7 weeks) were analyzed. The superior cerebellar peduncle was identified in 39 subjects (69%), and it was symmetric in 15 (38%). The middle cerebellar peduncle was identified in all subjects and appeared symmetric; in 13 subjects (22%), two distinct subcomponents were identified. The inferior cerebellar peduncle was not found in any subject. There was a significant increase in volume for the superior cerebellar peduncle and middle cerebellar peduncle (both, P < .05), an increase in fractional anisotropy (both, P < .001), and a decrease in ADC (both, P < .001) with gestational age. The middle cerebellar peduncle had higher volume (P < .001) and fractional anisotropy (P = .002) and lower ADC (P < .001) than the superior cerebellar peduncle after controlling for gestational age.

CONCLUSIONS

A robust motion-tracked section-to-volume registration algorithm enabled deterministic tractography of the superior cerebellar peduncle and middle cerebellar peduncle in vivo and allowed characterization of developmental changes.

Working Memory Impairments in Cerebellar Disorders of Childhood

The cerebellum is a crucial center for motor control and integration. Increasing evidence supports the notion that the cerebellum is also involved in nonmotor functions. Along these lines, multiple cerebellar disorders of childhood and adulthood are associated with behavioral and cognitive symptoms, including impairments in memory. One form of memory commonly affected in cerebellar disorders is working memory, which uses attention to manipulate information that is immediately available to execute cognitive tasks. This article reviews the literature illustrating that working memory impairments are frequently observed in acquired, congenital, and genetic/developmental cerebellar disorders of childhood. Functional neuroimaging studies demonstrate that working memory tasks engage many posterior regions of the cerebellar hemispheres and vermis. Thus, the cerebellum acts as one important node in the working memory circuit, and when the cerebellum is involved in childhood disorders, deficits in working memory commonly occur.

Short- and Long-Term Neurodevelopmental Outcomes of Very Preterm Infants with Neonatal Sepsis: A Systematic Review and Meta-Analysis

Sepsis is commonly experienced by infants born very preterm (<32 weeks gestational age and/or <1500 g birthweight), but the long-term functional outcomes are unclear. The objective of this systematic review was to identify observational studies comparing neurodevelopmental outcomes in very preterm infants who had blood culture-proven neonatal sepsis with those without sepsis. Twenty-four studies were identified, of which 19 used prespecified definitions of neurodevelopmental impairment and five reported neurodevelopmental outcomes as continuous variables. Meta-analysis was conducted using 14 studies with defined neurodevelopmental impairment and demonstrated that very preterm infants with neonatal sepsis were at higher risk of impairments, such as cerebral palsy and neurosensory deficits, compared with infants without sepsis (OR 3.18; 95% CI 2.29–4.41). Substantial heterogeneity existed across the studies (I² = 83.1, 95% CI 73–89). The five studies that reported outcomes as continuous variables showed no significant difference in cognitive performance between sepsis and non-sepsis groups. Neonatal sepsis in very preterm infants is associated with increased risk of neurodevelopmental disability. Due to the paucity of longitudinal follow-up data beyond 36 months, the long-term cognitive effect of neonatal sepsis in very preterm infants could not be conclusively determined. Effects on the development of minor impairment could not be assessed, due to the small numbers of infants included in the studies.

Microstructural abnormalities found in uncinate fasciculus and superior cerebellar tracts in children with global developmental delay: a feasibility study

AIM

To evaluate the microstructural abnormalities of the white matter tracts (WMT) using diffusion tensor imaging (DTI) in children with global developmental delay (GDD).

MATERIALS AND METHODS

Sixteen children with GDD underwent magnetic resonance imaging (MRI) and cross-sectional DTI. Formal developmental assessment of all GDD patients was performed using the Mullen Scales of Early Learning. An automated processing pipeline for the WMT assessment was implemented. The DTI-derived metrics of the children with GDD were compared to healthy children with normal development (ND).

RESULTS

Only two out of the 17 WMT demonstrated significant differences (p<0.05) in DTI parameters between the GDD and ND group. In the uncinate fasciculus (UF), the GDD group had lower mean values for fractional anisotropy (FA; 0.40 versus 0.44), higher values for mean diffusivity (0.96 versus 0.91×10^-3 mm²/s) and radial diffusivity (0.75 versus 0.68×10^-3 mm²/s) compared to the ND group. In the superior cerebellar peduncle (SCP), mean FA values were lower for the GDD group (0.38 versus 0.40). Normal myelination pattern of DTI parameters was deviated against age for GDD group for UF and SCP.

CONCLUSION

The UF and SCP WMT showed microstructural changes suggestive of compromised white matter maturation in children with GDD. The DTI metrics have potential as imaging markers for inadequate white matter maturation in GDD children.

Test-retest reproducibility of white matter parcellation using diffusion MRI tractography fiber clustering

There are two popular approaches for automated white matter parcellation using diffusion MRI tractography, including fiber clustering strategies that group white matter fibers according to their geometric trajectories and cortical-parcellation-based strategies that focus on the structural connectivity among different brain regions of interest. While multiple studies have assessed test-retest reproducibility of automated white matter parcellations using cortical-parcellation-based strategies, there are no existing studies of test-retest reproducibility of fiber clustering parcellation. In this work, we perform what we believe is the first study of fiber clustering white matter parcellation test-retest reproducibility. The assessment is performed on three test-retest diffusion MRI datasets including a total of 255 subjects across genders, a broad age range (5-82 years), health conditions (autism, Parkinson's disease and healthy subjects), and imaging acquisition protocols (three different sites). A comprehensive evaluation is conducted for a fiber clustering method that leverages an anatomically curated fiber clustering white matter atlas, with comparison to a popular cortical-parcellation-based method. The two methods are compared for the two main white matter parcellation applications of dividing the entire white matter into parcels (i.e., whole brain white matter parcellation) and identifying particular anatomical fiber tracts (i.e., anatomical fiber tract parcellation). Test-retest reproducibility is measured using both geometric and diffusion features, including volumetric overlap (wDice) and relative difference of fractional anisotropy. Our experimental results in general indicate that the fiber clustering method produced more reproducible white matter parcellations than the cortical-parcellation-based method.

Clinical application of advanced MR methods in children: points to consider

The application of both functional MRI and diffusion MR tractography prior to a neurosurgical operation is well established in adults, but less so in children, for several reasons. For this review, we have identified several aspects (task design, subject preparation, actual scanning session, data processing, interpretation of results, and decision-making) where pediatric peculiarities should be taken into account. Further, we not only systematically identify common issues, but also provide solutions, based on our experience as well as a review of the pertinent literature. The aim is to provide the clinician as well as the imaging scientist with information that helps to plan, conduct, and interpret such a clinically-indicated exam in a way that maximizes benefit for, and minimizes the burden on the individual child.

An anatomically curated fiber clustering white matter atlas for consistent white matter tract parcellation across the lifespan

This work presents an anatomically curated white matter atlas to enable consistent white matter tract parcellation across different populations. Leveraging a well-established computational pipeline for fiber clustering, we create a tract-based white matter atlas including information from 100 subjects. A novel anatomical annotation method is proposed that leverages population-based brain anatomical information and expert neuroanatomical knowledge to annotate and categorize the fiber clusters. A total of 256 white matter structures are annotated in the proposed atlas, which provides one of the most comprehensive tract-based white matter atlases covering the entire brain to date. These structures are composed of 58 deep white matter tracts including major long range association and projection tracts, commissural tracts, and tracts related to the brainstem and cerebellar connections, plus 198 short and medium range superficial fiber clusters organized into 16 categories according to the brain lobes they connect. Potential false positive connections are annotated in the atlas to enable their exclusion from analysis or visualization. In addition, the proposed atlas allows for a whole brain white matter parcellation into 800 fiber clusters to enable whole brain connectivity analyses. The atlas and related computational tools are open-source and publicly available. We evaluate the proposed atlas using a testing dataset of 584 diffusion MRI scans from multiple independently acquired populations, across genders, the lifespan (1 day-82 years), and different health conditions (healthy control, neuropsychiatric disorders, and brain tumor patients). Experimental results show successful white matter parcellation across subjects from different populations acquired on multiple scanners, irrespective of age, gender or disease indications. Over 99% of the fiber tracts annotated in the atlas were detected in all subjects on average. One advantage in terms of robustness is that the tract-based pipeline does not require any cortical or subcortical segmentations, which can have limited success in young children and patients with brain tumors or other structural lesions. We believe this is the first demonstration of consistent automated white matter tract parcellation across the full lifespan from birth to advanced age.

Longitudinal Preterm Cerebellar Volume: Perinatal and Neurodevelopmental Outcome Associations

Impaired cerebellar development is an important determinant of adverse motor and cognitive outcomes in very preterm (VPT) infants. However, longitudinal MRI studies investigating cerebellar maturation from birth through childhood and associated neurodevelopmental outcomes are lacking. We aimed to compare cerebellar volume and growth from term-equivalent age (TEA) to 7 years between VPT (< 30 weeks' gestation or < 1250 g) and full-term children; and to assess the association between these measures, perinatal factors, and 7-year outcomes in VPT children, and whether these relationships varied by sex. In a prospective cohort study of 224 VPT and 46 full-term infants, cerebellar volumes were measured on MRI at TEA and 7 years. Useable data at either time-point were collected for 207 VPT and 43 full-term children. Cerebellar growth from TEA to 7 years was compared between VPT and full-term children. Associations with perinatal factors and 7-year outcomes were investigated in VPT children. VPT children had smaller TEA and 7-year volumes and reduced growth. Perinatal factors were associated with smaller cerebellar volume and growth between TEA and 7 years, namely, postnatal corticosteroids for TEA volume, and female sex, earlier birth gestation, white and deep nuclear gray matter injury for 7-year volume and growth. Smaller TEA and 7-year volumes, and reduced growth were associated with poorer 7-year IQ, language, and motor function, with differential relationships observed for male and female children. Our findings indicate that cerebellar growth from TEA to 7 years is impaired in VPT children and relates to early perinatal factors and 7-year outcomes.

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.

Probing the neuroanatomy of the cerebellum using tractography

Diffusion tensor imaging (DTI) is a noninvasive neuroimaging tool assessing the organization of white-matter tracts and brain microstructure in vivo. The technique takes into account the three-dimensional (3D) direction of diffusion of water in space, the brownian movements of water being constrained by the brain microstructure. The main direction of diffusion in the brain is extracted to obtain the principal direction of axonal projection within a given voxel. Overall, the diffusion tensor is a mathematic analysis of the magnitude/directionality (anisotropy) of the movement of water molecules in 3D space. Tracts running in the white matter are subsequently reconstructed graphically with fiber tractography. Tractography can be applied to myelinated and unmyelinated fibers or axonopathy. Decreased fractional anisotropy in white-matter tracts occurs in cases of injury with disorganized or disrupted myelin sheaths. Furthermore, high angular resolution methods enable detection of fiber crossings or convergence. DTI is a modern tool which complements conventional magnetic resonance techniques and is particularly relevant to assess the organization of cerebellar tracts. Indeed, both the afferent and efferent pathways of the cerebellar circuitry passing through the inferior, middle, and superior cerebellar peduncles can be visualized in vivo, including in children. The microanatomy of the cerebellar cortex and cerebellar nuclei is also emerging as a future assessment. Applications in the field of cerebellar disorders are multiple, ranging from developmental disorders to adult-onset cerebellar ataxias.