A new study identifies five stages of human brain aging

Scientists at the University of Cambridge have found that the human brain goes through several clearly defined phases throughout life, with key turning points occurring at ages 9, 32, 66, and 83. The authors of the study hope that understanding the brain’s condition at each of these stages will help shed light on the causes of mental disorders and dementia.

Around 4,000 people aged up to 90 took part in the study. The researchers scanned their brains to determine how connections between brain cells function.

The Cambridge team concluded that the brain remains in a “youth phase” until roughly age 30 — a period widely considered the peak of human physical and cognitive performance.

According to the scientists, the new findings may help explain why the risks of mental disorders and dementia vary at different stages of life.

The research findings were published in the journal Nature Communications.

While the brain continually changes as it acquires new knowledge and experience, the study shows that this is not one smooth process from birth to death.

Instead, there are five distinct phases of brain function:

• Childhood — from birth to age 9

• Youth — from 9 to 32

• Adulthood — from 32 to 66

• Early aging — from 66 to 83

• Late aging — from 83 onward

“The brain reconfigures itself throughout life. It constantly strengthens some connections and weakens others, and this is not a steady, even process — there are fluctuations and phases of reorganization,” Dr. Alexa Mousley, one of the study’s authors, told the BBC.

These stages may begin earlier or later in some individuals, but the age thresholds above were the most common patterns observed in brain scans of the participants.

Childhood. During this initial period, the brain grows rapidly in size but simultaneously prunes excess synapses — the connections between nerve cells that were created early in life.
At this stage, the brain works less efficiently. It behaves like a child wandering aimlessly through a park, walking wherever they feel like going instead of moving directly from point A to point B.

Youth. Everything changes sharply around age nine, when the brain’s connections begin to reorganize for maximum efficiency. “It’s a huge shift,” says Dr. Mousley, calling the transition between these phases the most significant in a person’s life.
This is also when the risk of mental disorders is highest.

It is not surprising that the youth phase begins around puberty. But the new study suggests that it ends much later than previously thought.
It was once believed that youth ended with the teen years; later neuroscience extended it into the twenties — and now, into the early thirties.

This is the only phase in which the brain’s neural networks become more efficient. According to Mousley, brain performance peaks in the early years after turning 30 — at the very end of the 9-to-32 phase. She calls it “extremely interesting” that the brain remains in a single developmental phase for such a long period.

Adulthood. A period of stability follows — the longest phase of brain life, lasting around three decades.
Changes occur much more slowly than during the earlier, more turbulent years, but this is when the brain’s developmental processes begin to reverse.
According to the researchers, this is when we reach a kind of “plateau of intelligence and personality.”

Early aging. This stage begins around age 66, though it is not a sudden decline in brain efficiency. Instead, the patterns of neural connectivity begin to shift.
Rather than functioning as a single coordinated organ, the brain becomes increasingly divided into separate regions that still interact closely — like members of a band who start pursuing their own solo projects.

Although the study focused on healthy brains, this is typically the age at which dementia and high blood pressure — both of which affect brain function — begin to appear.

Late aging. Then, around age 83, we enter the final stage. Less data was available for this age group because it was harder to find enough healthy individuals for scanning.
Brain changes at this stage resemble those of early aging but are more pronounced.

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