08.09.2023 New publication: Human white matter myelinates faster in utero than ex utero

We are happy to announce the publication of a new papper called "Human white matter myelinates faster in utero than ex utero" in collaboration with researchers from the University of Washington and Stanford University.

Coordinated communication across the brain is supported by myelin, a fatty sheath that insulates nerve fibers. The growth of myelin progresses rapidly during early life and is essential for healthy brain development. Here, we ask what impact birth has on myelin growths in the brain’s white matter, evaluating large samples of infants born full-term or preterm. Birth drastically changes the infant’s experiences—moving them out of the sheltered environment of the womb, while increasing their sensory input. We find faster myelin growth in utero than ex utero and that the slower ex utero growth explains reduced myelin contents seen in preterm infants. We hypothesize that simulating a womb-like environment may promote myelin growth and cognitive outcomes in preterm infants.

The formation of myelin, the fatty sheath that insulates nerve fibers, is critical for healthy brain function. A fundamental open question is what impact being born has on myelin growth. To address this, we evaluated a large (n = 300) cross-sectional sample of newborns from the Developing Human Connectome Project (dHCP). First, we developed software for the automated identification of 20 white matter bundles in individual newborns that is well suited for large samples. Next, we fit linear models that quantify how T1w/T2w (a myelin-sensitive imaging contrast) changes over time at each point along the bundles. We found faster growth of T1w/T2w along the lengths of all bundles before birth than right after birth. Further, in a separate longitudinal sample of preterm infants (N = 34), we found lower T1w/T2w than in full-term peers measured at the same age. By applying the linear models fit on the cross-section sample to the longitudinal sample of preterm infants, we find that their delay in T1w/T2w growth is well explained by the amount of time they spent developing in utero and ex utero. These results suggest that white matter myelinates faster in utero than ex utero. The reduced rate of myelin growth after birth, in turn, explains lower myelin content in individuals born preterm and could account for long-term cognitive, neurological, and developmental consequences of preterm birth. We hypothesize that closely matching the environment of infants born preterm to what they would have experienced in the womb may reduce delays in myelin growth and hence improve developmental outcomes.

Mareike Grotheer & al.: Human white matter myelinates faster in utero than ex utero, PNAS 2023, DOI: https://doi.org/10.1073/pnas.2303491120