The cellular correlates and adolescent reorganisation of cortical myelination networks in the common marmoset

Structural similarity provides a powerful framework for measuring coordinated macro- and micro-structural variation across the cortex of a single brain. Similarity networks derived from myelin-sensitive MRI sequences undergo marked reorganisation during adolescence, linked to adversity exposure and behavioural outcomes in humans and rodents. However, the cellular mechanisms of MRI similarity and its development in non-human primate cortex remain unexplored. Here, we use myelin-sensitive T1w/T2w ratio images from a cross-sectional sample of 446 common marmosets (aged 0.62 to 12.75 years) to estimate MIND (Morphometric INverse Divergence) as a measure of myelination similarity in individual animals. We find that MIND metrics of myelination similarity are highly correlated with spatial gene expression of myelin basic protein (MBP) and other genes enriched in glutamatergic neurons and PV+ and VIP+ interneurons, reflecting the activity dependence of myelination. Across adolescence, network phenotypes accurately predict animal age and reproducibly capture an axis of myeloarchitectonic maturation spanning primary to transmodal association cortices, consistent with patterns observed in humans. Similarity mapping is a biologically validated and technically reliable measure of cortical myelination networks that can advance our understanding of phylogenetically conserved patterns of myelination network development in the marmoset cortex.