Atypical brain structure mediates reduced IQ in young adults born preterm with very low birth weight

The impact of socio-environmental factors on brain structure over the early life course of preterm-born individuals - A systematic review

BACKGROUND

Approximately 11 % of births worldwide are preterm (<37 weeks). While research traditionally focuses on complications of prematurity and brain development, the role of socio-environmental factors has received less attention. Recent studies indicate these factors significantly influence neurocognitive outcomes and brain development, beyond prematurity alone. This review examines the impact of socio-environmental factors on brain structure and function in preterm-born individuals from birth to early adulthood.

METHOD

We conducted searches in PubMed, Embase, and Web of Science for studies up to August 28th, 2024, examining socio-environmental effects on brain structure or function in preterm-born individuals using magnetic resonance imaging. From 891 articles screened, 23 met the inclusion criteria.

RESULTS

Socio-environmental factors, including socioeconomic status, prenatal conditions, hospital environment, and early life experiences, notably affect brain structures in preterm-born individuals. Key impacts were found in limbic and associative cortices (e.g., cingulate gyrus, parieto-temporal cortices), white matter tracts involved in executive functioning (e.g., superior longitudinal fasciculus, cingulum), and overall brain volume. Most studies focused on infancy, with 18 of 23 presenting data from the first year of life.

CONCLUSION

Socio-environmental factors are associated with changes in grey and white matter in the brain, especially in the limbic system and associative areas. These findings underscore the influence of early environments on preterm-born brain development, but long-term impacts remain unclear due to limited data beyond infancy.

Consistently lower volumes across thalamus nuclei in very premature-born adults

Lasting thalamus volume reduction after preterm birth is a prominent finding. However, whether thalamic nuclei volumes are affected differentially by preterm birth and whether nuclei aberrations are relevant for cognitive functioning remains unknown. Using T1-weighted MR-images of 83 adults born very preterm (≤ 32 weeks' gestation; VP) and/or with very low body weight (≤ 1,500 g; VLBW) as well as of 92 full-term born (≥ 37 weeks' gestation) controls, we compared thalamic nuclei volumes of six subregions (anterior, lateral, ventral, intralaminar, medial, and pulvinar) across groups at the age of 26 years. To characterize the functional relevance of volume aberrations, cognitive performance was assessed by full-scale intelligence quotient using the Wechsler Adult Intelligence Scale and linked to volume reductions using multiple linear regression analyses. Thalamic volumes were significantly lower across all examined nuclei in VP/VLBW adults compared to controls, suggesting an overall rather than focal impairment. Lower nuclei volumes were linked to higher intensity of neonatal treatment, indicating vulnerability to stress exposure after birth. Furthermore, we found that single results for lateral, medial, and pulvinar nuclei volumes were associated with full-scale intelligence quotient in preterm adults, albeit not surviving correction for multiple hypotheses testing. These findings provide evidence that lower thalamic volume in preterm adults is observable across all subregions rather than focused on single nuclei. Data suggest the same mechanisms of aberrant thalamus development across all nuclei after premature birth.

Language performance and brain volumes, asymmetry, and cortical thickness in children born extremely preterm

BACKGROUND

Children born preterm are more prone to have language difficulties. Few studies focus on children born extremely preterm (EPT) and the structural differences in language-related regions between these children and children born at term.

METHODS

Our study used T1-weighted magnetic resonance imaging (MRI) scans to calculate the brain volumetry, brain asymmetry, and cortical thickness of language-related regions in 50 children born EPT and 37 term-born controls at 10 years of age. The language abilities of 41 of the children born EPT and 29 term-born controls were then assessed at 12 years of age, using the Wechsler Intelligence Scale for Children, Fifth Edition and the Clinical Evaluations of Language Fundamentals, Fourth Edition. The differences between MRI parameters and their associations with language outcomes were compared in the two groups.

RESULTS

Brain volume and cortical thickness of language-related regions were reduced in children born EPT, but volumetric asymmetry was not different between children born EPT and at term. In children born EPT the brain volume was related to language outcomes, prior to adjustments for full-scale IQ.

CONCLUSIONS

These findings expand our understanding of the structural correlates underlying impaired language performance in children born with EPT.

IMPACT

The article expands understanding of the structure-function relationship between magnetic resonance imaging measurements of language-related regions and language outcomes for children born extremely preterm beyond infancy. Most literature to date has focused on very preterm children, but the focus in this paper is on extreme prematurity and language outcomes. While the brain volume and cortical thickness of language-related regions were reduced in children born EPT only the volume, prior to adjustment for full-scale IQ, was associated with language outcomes. We found no differences in volumetric asymmetry between children born EPT and at term.

Association between cortical thickness and cognitive ability in very preterm school-age children

Very preterm children, born before 32 weeks of gestation, are at risk for impaired cognitive function, mediated by several risk factors. Cognitive impairment can be measured by various neurodevelopmental assessments and is closely associated with structural alterations of brain morphometry, such as cortical thickness. However, the association between structural alterations and high-order cognitive function remains unclear. This study aimed to investigate the neurodevelopmental associations between brain structural changes and cognitive abilities in very preterm and full-term children. Cortical thickness was assessed in 37 very preterm and 24 full-term children aged 6 years. Cortical thickness analysis of structural T1-weighted images was performed using Advanced Normalization Tools. Associations between cortical thickness and the Wechsler Intelligence Scale for Children were evaluated by regression analysis based on ordinary least square estimation. Compared with full-term children, very preterm children showed significant differences in cortical thickness, variously associated with cognitive abilities in several brain regions. Perceptual reasoning indices were broadly correlated with cortical thickness in very preterm and full-term children. These findings provide important insights into neurodevelopment and its association with cortical thickness, which may serve as a biomarker in predictive models for neurodevelopmental diagnosis of high-order cognitive function.

Timing of lifespan influences on brain and cognition

Modifiable risk and protective factors for boosting brain and cognitive development and preventing neurodegeneration and cognitive decline are embraced in neuroimaging studies. We call for sobriety regarding the timing and quantity of such influences on brain and cognition. Individual differences in the level of brain and cognition, many of which present already at birth and early in development, appear stable, larger, and more pervasive than differences in change across the lifespan. Incorporating early-life factors, including genetics, and investigating both level and change will reduce the risk of ascribing undue importance and causality to proximate factors in adulthood and older age. This has implications for both mechanistic understanding and prevention.