Socioeconomic disadvantage and episodic memory ability in the ABCD sample: Contributions of hippocampal subregion and subfield volumes

A general exposome factor explains individual differences in functional brain network topography and cognition in youth

Childhood environments are critical in shaping cognitive neurodevelopment. With the increasing availability of large-scale neuroimaging datasets with deep phenotyping of childhood environments, we can now build upon prior studies that have considered relationships between one or a handful of environmental and neuroimaging features at a time. Here, we characterize the combined effects of hundreds of inter-connected and co-occurring features of a child's environment ("exposome") and investigate associations with each child's unique, multidimensional pattern of functional brain network organization ("functional topography") and cognition. We apply data-driven computational models to measure the exposome and define personalized functional brain networks in pre-registered analyses. Across matched discovery (n=5139, 48.5% female) and replication (n=5137, 47.1% female) samples from the Adolescent Brain Cognitive Development study, the exposome was associated with current (ages 9-10) and future (ages 11-12) cognition. Changes in the exposome were also associated with changes in cognition after accounting for baseline scores. Cross-validated ridge regressions revealed that the exposome is reflected in functional topography and can predict performance across cognitive domains. Importantly, a single measure capturing a child's exposome could more accurately and parsimoniously predict cognition than a wealth of personalized neuroimaging data, highlighting the importance of children's complex, multidimensional environments in cognitive neurodevelopment.

Age differences in generalization, memory specificity, and their overnight fate in childhood

Memory enables generalization to new situations, and memory specificity that preserves individual episodes. This study investigated generalization, memory specificity, and their overnight fate in 141 4- to 8-year-olds (computerized memory game; 71 females, tested 2020-2021 in Germany). The results replicated age effects in generalization and memory specificity, and a contingency of generalization on object conceptual properties and interobject semantic proximity. Age effects were stronger in generalization than in memory specificity, and generalization was more closely linked to the explicit regularity knowledge in older than in younger children. After an overnight delay, older children retained more generalized and specific memories and showed greater gains but only in generalization. These findings reveal distinct age differences in generalization and memory specificity across childhood.

Shared and unique heritability of hippocampal subregion volumes in children and adults

Behavioral genetic analyses have not demonstrated robust, unique, genetic correlates of hippocampal subregion volume. Genetic differentiation of hippocampal longitudinal axis subregion volume has not yet been investigated in population-based samples, although this has been demonstrated in rodent and post-mortem human tissue work. The following study is the first population-based investigation of genetic factors that contribute to gray matter volume along the hippocampal longitudinal axis. Twin-based biometric analyses demonstrated that longitudinal axis subregions are associated with significant, unique, genetic variance, and that longitudinal axis subregions are also associated with significant shared, hippocampus-general, genetic factors. Our study's findings suggest that genetic differences in hippocampal longitudinal axis structure can be detected in individual differences in gray matter volume in population-level research designs.

Polygenic risk for depression and anterior and posterior hippocampal volume in children and adolescents

BACKGROUND

Depression has frequently been associated with smaller hippocampal volume. The hippocampus varies in function along its anterior-posterior axis, with the anterior hippocampus more strongly associated with stress and emotion processing. The goals of this study were to examine the associations among parental history of anxiety/depression, polygenic risk scores for depression (PGS-DEP), and anterior and posterior hippocampal volumes in children and adolescents. To examine specificity to PGS-DEP, we examined associations of educational attainment polygenic scores (PGS-EA) with anterior and posterior hippocampal volume.

METHODS

Participants were 350 3- to 21-year-olds (46 % female). PGS-DEP and PGS-EA were computed based on recent, large-scale genome-wide association studies. High-resolution, T1-weighted magnetic resonance imaging (MRI) data were acquired, and a semi-automated approach was used to segment the hippocampus into anterior and posterior subregions.

RESULTS

Children and adolescents with higher polygenic risk for depression were more likely to have a parent with a history of anxiety/depression. Higher polygenic risk for depression was significantly associated with smaller anterior but not posterior hippocampal volume. PGS-EA was not associated with anterior or posterior hippocampal volumes.

LIMITATIONS

Participants in these analyses were all of European ancestry.

CONCLUSIONS

Polygenic risk for depression may lead to smaller anterior but not posterior hippocampal volume in children and adolescents, and there may be specificity of these effects to PGS-DEP rather than PGS-EA. These findings may inform the earlier identification of those in need of support and the design of more effective, personalized treatment strategies.

DECLARATIONS OF INTEREST

none.

DECLARATIONS OF INTEREST

None.

Personalized functional brain network topography is associated with individual differences in youth cognition

Individual differences in cognition during childhood are associated with important social, physical, and mental health outcomes in adolescence and adulthood. Given that cortical surface arealization during development reflects the brain's functional prioritization, quantifying variation in the topography of functional brain networks across the developing cortex may provide insight regarding individual differences in cognition. We test this idea by defining personalized functional networks (PFNs) that account for interindividual heterogeneity in functional brain network topography in 9-10 year olds from the Adolescent Brain Cognitive Development℠ Study. Across matched discovery (n = 3525) and replication (n = 3447) samples, the total cortical representation of fronto-parietal PFNs positively correlates with general cognition. Cross-validated ridge regressions trained on PFN topography predict cognition in unseen data across domains, with prediction accuracy increasing along the cortex's sensorimotor-association organizational axis. These results establish that functional network topography heterogeneity is associated with individual differences in cognition before the critical transition into adolescence.

Age-related differences in hippocampal subfield volumes across the human lifespan: A meta-analysis

The human hippocampus (Hc) is critical for memory function across the lifespan. It is comprised of cytoarchitectonically distinct subfields: dentate gyrus (DG), cornu ammonis sectors (CA) 1-4, and subiculum, each of which may be differentially susceptible to neurodevelopmental and neurodegenerative mechanisms. Identifying age-related differences in Hc subfield volumes can provide insights into neural mechanisms of memory function across the lifespan. Limited evidence suggests that DG and CA3 volumes differ across development while other regions remain relatively stable, and studies of adulthood implicate a downward trend in all subfield volumes with prominent age effects on CA1. Due to differences in methods and limited sampling for any single study, the magnitude of age effects on Hc subfield volumes and their probable lifespan trajectories remain unclear. Here, we conducted a meta-analysis on cross-sectional studies (n = 48,278 participants, ages = 4-94 years) to examine the association between age and Hc subfield volumes in development (n = 11 studies), adulthood (n = 30 studies), and a combined lifespan sample (n = 41 studies) while adjusting estimates for sample sizes. In development, age was positively associated with DG and CA3-4 volumes, whereas in adulthood a negative association was observed with all subfield volumes. Notably, the observed age effects were not different across subfield volumes within each age group. All subfield volumes showed a nonlinear age pattern across the lifespan with DG and CA3-4 volumes showing a more distinct age trajectory as compared to the other subfields. Lastly, among all the study-level variables, only female percentage of the study sample moderated the age effect on CA1 volume: a higher female-to-male ratio in the study sample was linked to the greater negative association between age and CA1 volume. These results document that Hc subfield volumes differ as a function of age offering broader implications for constructing theoretical models of lifespan memory development.

Household socioeconomic status relates to specific hippocampal subfield volumes across development

The hippocampus is composed of cytoarchitecturally distinct subfields that support specific memory functions. Variations in total hippocampal volume across development have been linked to socioeconomic status (SES), a proxy for access to material resources, medical care, and quality education. High childhood household SES is associated with greater cognitive abilities in adulthood. Currently, it is not known whether household SES differentially impacts specific hippocampal subfield volumes. We assessed susceptibility of subfields to variations in household SES across development in a sample of 167 typically developing 5- to 25-year-old. Bilateral cornu ammonis (CA) 1-2, combined CA3-dentate gyrus (DG), and subiculum (Sub) volumes were measured by highly reliable manual segmentation of high-resolution T2-weighted images and adjusted for intracranial volume. A summary component score of SES measures (paternal education, maternal education, and income-to-needs ratio) was used to examine variability in volumes across ages. We did not identify age-related differences in any of the regional volumes, nor did age modify SES-related effects. Controlling for age, larger volumes of CA3-DG and CA1-2 were associated with lower SES, while Sub volume was not. Overall, these findings support the specific impact of SES on CA3-DG and CA1-2 and highlight the importance of considering environmental influences on hippocampal subfield development.

Polygenic Risk for Schizophrenia, Major Depression, and Post-traumatic Stress Disorder and Hippocampal Subregion Volumes in Middle Childhood

Studies demonstrate that individuals with diagnoses for Major Depressive Disorder (MDD), Post-traumatic Stress Disorder (PTSD), and Schizophrenia (SCZ) may exhibit smaller hippocampal gray matter relative to otherwise healthy controls, although the effect sizes vary in each disorder. Existing work suggests that hippocampal abnormalities in each disorder may be attributable to genetic liability and/or environmental variables. The following study uses baseline data from the Adolescent Brain and Cognitive Development[Formula: see text] Study (ABCD Study[Formula: see text]) to address three open questions regarding the relationship between genetic risk for each disorder and hippocampal volume reductions: (a) whether polygenic risk scores (PGRS) for MDD, PTSD, and SCZ are related to hippocampal volume; (b) whether PGRS for MDD, PTSD, and SCZ are differentially related to specific hippocampal subregions along the longitudinal axis; and (c) whether the association between PGRS for MDD, PTSD, and SCZ and hippocampal volume is moderated by sex and/or environmental adversity. In short, we did not find associations between PGRS for MDD, PTSD, and SCZ to be significantly related to any hippocampal subregion volumes. Furthermore, neither sex nor enviornmental adversity significantly moderated these associations. Our study provides an important null finding on the relationship genetic risk for MDD, PTSD, and SCZ to measures of hippocampal volume.

Impact of Socioeconomic Status on Amygdala and Hippocampus Subdivisions in Children and Adolescents

Socioeconomic status (SES) in childhood can impact behavioral and brain development. Past work has consistently focused on the amygdala and hippocampus, two brain areas critical for emotion and behavioral responding. While there are SES differences in amygdala and hippocampal volumes, there are many unanswered questions in this domain connected to neurobiological specificity, and for whom these effects may be more pronounced. We may be able to investigate some anatomical subdivisions of these brain areas, as well as if relations with SES vary by participant age and sex. No work to date has however completed these types of analyses. To overcome these limitations, here, we combined multiple, large neuroimaging datasets of children and adolescents with information about neurobiology and SES (N=2,765). We examined subdivisions of the amygdala and hippocampus and found multiple amygdala subdivisions, as well as the head of the hippocampus, were related to SES. Greater volumes in these areas were seen for higher-SES youth participants. Looking at age- and sex-specific subgroups, we tended to see stronger effects in older participants, for both boys and girls. Paralleling effects for the full sample, we see significant positive associations between SES and volumes for the accessory basal amygdala and head of the hippocampus. We more consistently found associations between SES and volumes of the hippocampus and amygdala in boys (compared to girls). We discuss these results in relation to conceptions of "sex-as-a-biological variable" and broad patterns of neurodevelopment across childhood and adolescence. These results fill in important gaps on the impact of SES on neurobiology critical for emotion, memory, and learning.