Scientists reveal five big moments when your brain dramatically changes

A team from Cambridge's MRC Cognition and Brain Sciences Unit analyzed MRI diffusion scans from 3,802 individuals ranging from newborns to 90 years old. These scans track the movement of water through brain tissue, which helps researchers map the networks that link one region to another.

Their findings, published in Nature Communications, show that the brain's structure progresses through five broad phases. Four key "turning points" divide these phases, marking ages when the brain undergoes meaningful reorganization.

Childhood, Adolescence, and a Slow Path to Adulthood

The first epoch spans from birth to about age nine, when a major turning point leads into the adolescent phase. This adolescent period lasts much longer than expected, continuing until roughly age 32 on average.

In the early thirties, the brain's wiring shifts into an adult configuration. This becomes the longest era and continues for more than three decades. A third turning point near age 66 marks the beginning of an "early aging" phase, while the final "late aging" stage emerges around age 83.

"We know the brain's wiring is crucial to our development, but we lack a big picture of how it changes across our lives and why," said Dr. Alexa Mousley, a Gates Cambridge Scholar who led the research. "This study is the first to identify major phases of brain wiring across a human lifespan."

"These eras provide important context for what our brains might be best at, or more vulnerable to, at different stages of our lives. It could help us understand why some brains develop differently at key points in life, whether it be learning difficulties in childhood, or dementia in our later years."

Early Brain Growth: Synapses, Consolidation, and Rapid Change

From infancy through childhood, the brain is shaped by "network consolidation." Babies generate an enormous number of synapses, the points where neurons communicate. Over time, only the most active connections are kept while the rest are eliminated.

During this period, the entire brain follows a consistent rewiring pattern. Grey and white matter grow quickly, pushing cortical thickness (the distance between outer grey matter and inner white matter) to its highest point. The folds of the cerebral cortex also stabilize, forming the ridges seen on the outer surface.

By age nine, the brain encounters its first major turning point. Cognitive abilities expand rapidly at this age, but the risk of developing certain mental health conditions also becomes higher.

Adolescence: Increasing Efficiency and More Organized Brain Networks

The second epoch, adolescence, is marked by continued growth of white matter. As these pathways expand, the organization of communication networks becomes more refined. MRI diffusion scans show more orderly water movement in the tissue, reflecting stronger and more coordinated connections.

This period is notable for rising efficiency in how signals move both within individual regions and across the whole brain. These improvements are linked to gains in cognitive performance.

"Neural efficiency is as you might imagine, well connected by short paths, and the adolescent era is the only one in which this efficiency is increasing," said Mousley.

These changes peak in the early thirties, which researchers describe as the "strongest topological turning point" across the entire lifespan.

"Around the age of 32, we see the most directional changes in wiring and largest overall shift in trajectory, compared to all the other turning points," said Mousley. "While puberty offers a clear start, the end of adolescence is much harder to pin down scientifically. Based purely on neural architecture, we found that adolescent-like changes in brain structure end around the early thirties."

Adulthood: Stability and Gradual Compartmentalization

At approximately age 32, the adult epoch begins. This phase is relatively stable compared with earlier stages of life, and no additional major turning points appear for about thirty years. According to the researchers, this aligns with a "plateau in intelligence and personality" described in other studies.

They also noted growing "segregation" during this time, meaning that different brain regions begin to operate in more distinct and specialized ways.

The next turning point, around age 66, is much more subtle. While it does not involve dramatic structural changes, the team still observed meaningful shifts in network organization.

"The data suggest that a gradual reorganization of brain networks culminates in the mid-sixties," said Mousley. "This is probably related to aging, with further reduced connectivity as white matter starts to degenerate. This is an age when people face increased risk for a variety of health conditions that can affect the brain, such as hypertension."

Late Aging: Declining Global Connectivity and Regional Reliance

The final turning point arrives near age 83, signaling the start of the last brain structure epoch. Although the amount of data for this phase is limited, researchers found a clear pattern. The brain becomes less globally connected and depends more heavily on specific regions.

"Looking back, many of us feel our lives have been characterized by different phases. It turns out that brains also go through these eras," said senior author Prof Duncan Astle, Professor of Neuroinformatics at Cambridge.

"Many neurodevelopmental, mental health and neurological conditions are linked to the way the brain is wired. Indeed, differences in brain wiring predict difficulties with attention, language, memory, and a whole host of different behaviors."

"Understanding that the brain's structural journey is not a question of steady progression, but rather one of a few major turning points, will help us identify when and how its wiring is vulnerable to disruption."

The research received support from the Medical Research Council, the Gates Foundation, and the Templeton World Charitable Foundation.