A deep dive into hippocampus growth: Unveiling neurite and soma development with in vivo diffusion MRI

Motivation: The hippocampus serves multiple cognitive functions, yet little is known about its microstructural development. Goal(s): To leverage recent MRI hardware and microstructure modeling advances to capture hippocampal cell-body (soma) and projection (neurite) development during late-childhood and adolescence. Approach: Diffusion MRI data was acquired in 88 participants aged 8-18 years using a 3T Connectom scanner (with 300mT/m gradients), and analyzed using the Soma and Neurite Density Imaging model. Results: For the first time, we identified distinct developmental patterns of hippocampal microstructural subcomponents. Specifically, we found an age-related increase in neurite fraction and concurrent decrease in extracellular fraction and soma radius. Impact: We report, for the first time, distinct neurite and soma developmental profiles in the hippocampus during late childhood/adolescence. This forms a crucial baseline for understanding developmental disorders, and opens new avenues for corroborating in vivo diffusion with histology.