The brain develops in harmony

Imaging data from the Lise Meitner Group NeuroLearn suggests that the cerebral cortex and neural pathways mature together from the outset.

For the brain to function efficiently, nerve cells must transmit their signals rapidly. This is made possible by myelin, a fatty insulating layer that surrounds nerve fibers. A study shows that the brain’s long-range connection pathways and the cerebral cortex myelinate synchronously during the first months of life. The findings could fundamentally expand our understanding of the early development of neural networks.

Few organs change as rapidly during the first months of life as the brain. While infants learn to recognize faces, coordinate movements, and explore their environment, profound remodeling processes are taking place within the brain. Billions of nerve cells are already present, but it is only through their interconnectedness that they become a highly efficient communication system. Myelination plays a central role in this process: by building up the insulating myelin sheath, electrical signals can be transmitted faster, more reliably, and more efficiently. 

Until now, this process has generally been studied separately for different parts of the brain. Researchers have focused on the long nerve fibers of the white matter, which connect different brain regions, on the one hand, and on the gray matter, which contains neuronal cell bodies and is responsible for information processing, on the other. Both tissues develop dynamically during the first years of life. However, it has remained unclear whether their myelination proceeds independently or is coordinated from the outset. 

Do gray and white matter myelinate together? 

A research team from the Max Planck Institute for Human Development, Philipps University Marburg, and Stanford University now paints a more nuanced picture. Their study, published in Nature Communications, suggests that myelination in gray and white matter is tightly intertwined already during the first weeks of life. According to the findings, the brain does not build its “data lines” and corresponding processing centers independently from each other, but rather as a unified system. 

The study was based on two complementary datasets. The primary dataset consisted of MRI scans from 273 newborns participating in the Developing Human Connectome Project, one of the world’s largest studies of early brain development. In addition, the researchers analyzed quantitative MRI data from 21 infants enrolled in Stanford’s VPNL Baby Project. Both data sets contain metrics that capture tissue properties and are closely related to myelin content. Combining the two datasets allowed the researchers to independently validate their findings. 

Using automated analyses, the researchers reconstructed 26 major white matter bundles and identified their cortical targets. This enabled them, for the first time, to systematically investigate whether the development of a white matter bundle is related to the development of its corresponding cortical target.  

The answer was clear: white matter bundles with stronger myelin-sensitive MRI signals were associated with comparatively higher values in their corresponding cortical targets. Conversely, less-developed white matter bundles were linked to lower values in the connected cortical targets. This relationship was observed not only at the group level but also in individual children.  

Coupled myelination during the first weeks of life 

The relationship between the two tissue types became particularly apparent when the researchers examined the rate of myelination. During the first weeks of life, myelin-sensitive signals increased continuously in both white and gray matter. 

Crucially, however, the developmental rates mirrored one another: where white matter bundles myelinated particularly quickly, the connected cortical targets also developed more rapidly.  

Although myelination in white matter was generally more dynamic than in gray matter, the two processes remained closely coupled, as if communication pathways and processing centers were accompanying each other throughout development. 

Premature birth affects coordination 

The study also provides evidence that early deviations from typical development may disrupt this interaction between the two brain tissues. In preterm infants, the coupling of gray and white matter myelination was less pronounced than in infants born at term. 

Although synchrony increased with age, preterm infants had not yet fully reached the level of the comparison group even by their expected due date. These findings complement earlier studies that described the effects of prematurity on brain maturation and myelination. The new data suggest that not only the amount of myelin produced may be altered, but also its temporal coordination across different brain tissues. 

Relationship to motor development 

The researchers also examined whether early myelination synchrony is associated with later developmental outcomes. Indeed, children who showed stronger coupling of gray and white matter myelination at birth achieved slightly better motor performance at 17 to 25 months of age.  

The effect was statistically significant but relatively small. No comparable associations were found for language or cognitive abilities. The data do not allow conclusions about cause and effect. However, they do suggest that the temporal coordination of myelination across brain tissues may be related to motor development. 

Why do the two tissues develop in tandem? 

Why gray and white matter myelinate in such close coordination is not directly addressed by the study. However, the researchers discuss several possible mechanisms. One explanation is so-called activity-dependent myelination. According to this idea, active neurons promote myelin formation along their connections. If certain neural networks are used particularly intensively, myelination of both the connecting white matter pathways and the involved cortical targets could accelerate simultaneously. Shared genetic regulatory programs or coupled metabolic processes in both tissues are also conceivable.  

“Myelin was underestimated for a long time,” says neuroscientist Mareike Grotheer, head of the Lise Meitner Research Group NeuroLearn – Neuroplasticity in Development and Learning at the Max Planck Institute for Human Development. For many years, major nerve pathways were viewed as a largely static scaffold. Only in recent years has it become clear how closely myelination, learning, and brain plasticity are linked. 

Animal studies also demonstrate that myelin is far more than a passive insulating layer. When myelin formation is deliberately disrupted in mice, their learning performance declines substantially. In humans, however, research into these relationships is still in its early stages. 

A new perspective on early brain development 

The findings suggest that gray and white matter should no longer be considered in isolation. Instead, the study indicates that gray and white matter myelination proceeds in concert from the outset of life as part of a tightly coupled system.  

If the findings are confirmed in future studies, myelination synchrony could serve as an additional biomarker of infant brain development, particularly in preterm infants or children at increased developmental risk. 

At a glance 

• Joint development: Gray and white matter are myelinated synchronously during early infancy.
• Prematurity: In preterm infants, this synchrony is initially less pronounced.
• Motor development: Stronger coupling of gray and white matter myelination at birth is associated with slightly better motor performance in toddlerhood.
• New perspective: The findings support viewing gray and white matter myelination as a closely interconnected process.

How can myalin be measured in the brain?
Myelin is the fatty insulating layer that surrounds nerve fibers and accelerates the transmission of electrical signals. However, myelin cannot be visualized directly with magnetic resonance imaging (MRI). Instead, researchers use measures that are sensitive to tissue properties closely linked to myelin content.
In the present study, two different approaches were used. In the larger dataset, researchers analyzed the ratio between two MRI image types (T1-weighted and T2-weighted scans). This ratio can be used to estimate the degree of myelination in a brain region.
In addition, the researchers used a quantitative MRI method in a smaller group of infants. This approach produces not only images of the brain but also measurable numerical values that describe specific tissue properties. One of these measures, the longitudinal relaxation rate (R1), has been shown to be closely linked to myelin content and is widely used as a quantitative marker of myelination.
The key point is that both methods independently provided very similar results. This increases confidence that the observed synchrony between cortical and white matter myelination genuinely reflects biological myelin development rather than being an artifact of any single measurement technique. This makes the findings particularly robust. 

Originalpublikation

Zika, S., Chang, K., Orhon, A., Kruper, J., Tyagi, C., Yan, X., Tung, S., Grill-Spector, K., Rokem, A., & Grotheer, M. (2026). Cortical and white matter myelination proceed in concert during early infancy. Nature Communications, 17, Article 5353. https://doi.org/10.1038/s41467-026-73366-9