The structural development of the human brain does not proceed smoothly or linearly, but rather through a series of clearly defined stages with distinct “turning points.” This conclusion was reached by researchers who analyzed MRI data from thousands of people—from infants to 90-year-olds. The architecture of brain networks passes through five phases, separated by ages of approximately 9, 32, 66, and 83 years. The study was published in Nature Communications (NatCom).

Previously, it was believed that the brain develops along a relatively smooth trajectory: rapid growth in childhood, a peak in adulthood, and a gradual decline in old age. However, according to the authors, such models oversimplify reality and fail to capture complex nonlinear reorganizations. The new study proposes a “normative map”—a baseline description of how brain organization changes on average across the entire lifespan.

“We have long known that brain connections change with age, but we lacked an understanding of the general patterns underlying these changes,” explained the study’s lead author, Alexa Mousley, a postdoctoral researcher at the University of Cambridge. “This matters because the organization of brain networks is linked to neurodevelopment, psychiatric disorders, and neurological diseases.”

The team combined data from nine neuroimaging projects, assembling a sample of 4,216 individuals aged 0 to 90 years. To construct a reference trajectory, 3,802 scans from neurotypical participants were selected. The researchers used diffusion-weighted MRI, which allows mapping of white matter—the brain’s conducting “cables” that connect different regions.

The analysis revealed four key transition points dividing five stages. The first spans from birth to about 9 years and is associated with rapid formation and “pruning” of connections: overall efficiency decreases while local specialization increases. The second stage—from 9 to 32 years—proved unexpectedly long and resembles a prolonged “structural adolescence,” during which the brain actively increases network integration and information-transfer efficiency. The transition around age 32 was the most pronounced across the entire lifespan.

The third stage (32–66 years) is characterized by relative stability and a gradual increase in network segregation, aligning with psychological data on the stabilization of personality and cognitive functions. The fourth stage (66–83 years) reflects the onset of age-related changes and a decline in network integrity. Finally, after age 83, there is further weakening of global connectivity, with age-related dynamics becoming less pronounced.

Importantly, these structural “milestones” coincide with biological and social thresholds—such as puberty, peak physical development, and retirement. At the same time, the authors emphasized that the findings relate exclusively to brain architecture, not to behavior or levels of maturity.