White matter myelination during early infancy is linked to spatial gradients and myelin content at birth

Abstract

Development of myelin, a fatty sheath that insulates nerve fibers, is critical for brain function. Myelination during infancy has been studied with histology, but postmortem data cannot evaluate the longitudinal trajectory of white matter development. Here, we obtained longitudinal diffusion MRI and quantitative MRI measures of longitudinal relaxation rate (R1) of white matter in 0, 3 and 6 months-old human infants, and developed an automated method to identify white matter bundles and quantify their properties in each infant’s brain. We find that R1 increases from newborns to 6-months-olds in all bundles. R1 development is nonuniform: there is faster development in white matter that is less mature in newborns, and development rate increases along inferior-to-superior as well as anterior-to-posterior spatial gradients. As R1 is linearly related to myelin fraction in white matter bundles, these findings open new avenues to elucidate typical and atypical white matter myelination in early infancy.

The Potential of Myelin-Sensitive Imaging: Redefining Spatiotemporal Patterns of Myeloarchitecture

“…Myelinsensitive imaging is well posed to test these hypotheses, given the possibilities to examine myelin across the entire brain and to track individual developmental trajectories. In infants, Grotheer et al, (2022) showed that myelin levels at birth as well as spatial position contribute to age-related R1 changes in white matter bundles (Figure 4Ai). In certain tracts speed of myelination is inversely correlated to the pre-existing degree of myelin, whereas in other tracts it is associated with spatial axes (Figure 4Aii).…”

“…Notably, each dimension is sensitive to a different aspect of the myelin profile shape, related to myelin content at certain cortical depths [produced with data from (103)]. (133)]. ii.…”

“…ii. Examining bundle-specific myelin, the developmental rate ("slope", dotted line) is sometimes inversely correlated to R1 in newborns ("0m", full line) and other times correlated with a spatial axis (posterior-anterior depicted as xaxis) [reproduced from (133)]. CS=cortico-spinal.…”

“…A) i.Scatterplots represent sampling points along white matter bundles, coloured by (left) bundle, (centre) R1 in newborns and (right) development rate of R1 from 0-6months. Across all points, development rate could be largely explained (67% of variance) by R1 in newborns and spatial position (anterior-posterior and inferiorsuperior axes) [reproduced from(133)]. ii.…”

White matter connections of high-level visual areas predict cytoarchitecture better than category-selectivity in childhood, but not adulthood

“…Instead, it seems that white matter and cytoarchitecture are closely linked early in development, and that category-specific connections can emerge over development. Recent findings revealing that white matter fascicles can be reliably identified in individual newborns (Grotheer et al 2022) paving the way for future research to examine whether the relationship between cytoarchitecture and white matter connections is present at birth.…”