A Longitudinal Study of Children's Hippocampal Development: Investigating Maternal Physical Activity, Depression, and Education.

Bilateral hippocampal volume increased nonlinearly with age across childhood and early adolescence.

• Study included 113 children (59 females) with a mean age of 4.16 ± 1.25 years at first scan.
• A total of 510 MRI scans were collected longitudinally.
• Developmental trajectories were analyzed using generalized fractional polynomial mixed models.
• Volume increases were characterized as nonlinear over the developmental period studied.

Hippocampal diffusion metrics (FA, MD, and RD) changed in line with typical brain maturation patterns across development.

• Fractional anisotropy (FA), mean diffusivity (MD), and radial diffusivity (RD) were all measured.
• Changes in diffusion metrics were consistent with expected patterns of typical brain maturation.
• Diffusion MRI metrics were used alongside volumetric measures to characterize hippocampal development.
• Generalized fractional polynomial mixed models were used to capture potentially nonlinear trajectories.

Sex differences were found in FA development of the hippocampus.

• The sample included 59 females and 54 males.
• Sex differences were specifically identified in the developmental trajectory of fractional anisotropy (FA).
• No sex differences in FA development were pre-registered as a hypothesis, suggesting this was an observed finding.
• Sex differences were not reported for MD, RD, or hippocampal volume.

Prenatal maternal physical activity was not significantly associated with hippocampal structure in children.

• Maternal physical activity was assessed during the second trimester of pregnancy.
• This finding was in contrast to the authors' pre-registered hypotheses.
• Both hippocampal volume and diffusion metrics (FA, MD, RD) were examined as outcome measures.
• The lack of association was found across the longitudinal developmental period studied.

Prenatal maternal depression was not significantly associated with hippocampal structure in exploratory analyses.

• Maternal depressive symptoms were assessed during the second trimester.
• The analysis of maternal depression was conducted as an exploratory (non-pre-registered) analysis.
• Both hippocampal volume and diffusivity metrics were examined as outcomes.
• The absence of association was noted across bilateral hippocampal measures.

Maternal education was not significantly associated with hippocampal structure in exploratory analyses.

• Maternal education was examined as a predictor of hippocampal development in exploratory analyses.
• No significant associations were found with hippocampal volume or diffusion metrics.
• This analysis was not part of the pre-registered hypotheses.
• The finding suggests maternal education level does not strongly relate to hippocampal structure in this sample.