Your brain isn’t ‘adult’ until 32, study says. These are the 5 major phases from birth to old age

The brain changes as we age – but a new study pinpoints exactly when those shifts occur.

Our brain structure moves through five distinct phases marked by four turning points, at ages nine, 32, 66, and 83, according to the study, which was published in thejournal Nature Communications.

The research is the first to identify major phases of brain wiring across the lifespan, shedding new light on what our brains may be particularly vulnerable to during different life stages, for example, childhood learning disabilities and age-related conditions like dementia.

“Looking back, many of us feel our lives have been characterised by different phases,” said Duncan Astle, the study’s senior author and a professor of neuroinformatics at the University of Cambridge.

“It turns out that brains also go through these eras,” he added in a statement.

Astle’s team compared the brain scans of about 3,800 people aged zero to 90. The scans track how water molecules move through the brain, allowing the researchers to map neural connections and home in on key moments of developmental change across the lifespan.

During the first stage, from infancy to around age nine, billions of new neural connections are made and inactive ones are pruned, and both grey and water matter grow rapidly.

Grey matter processes and interprets information, while white matter transmits that information to other parts of the nervous system, serving as the brain’s communication network.

This process leads to peak cortical thickness and cortical folding – the ridges of the outer brain – which are both thought to be critical to brain health and development.

The brain then moves into the adolescent phase, defined by white matter growth and more efficient connections between different parts of the nervous system.

Notably, the adolescent period lasts until age 32 on average, the study found. It then transitions to the adult era, which the researchers called the “strongest topological turning point” of our lives.

The brain’s structure stabilises in the early 30s and then gets a three-decade break before entering another stage. Around age 66, the brain transitions into an “early ageing” phase, with white matter starting to degrade, reducing these connections.

“This is an age when people face increased risk for a variety of health conditions that can affect the brain, such as hypertension,” said Alexa Mousley, the study’s lead author and a University of Cambridge researcher.

The final stage begins around age 83, when connectivity continues to decline and the brain begins relying even more on certain regions – although data is limited for this phase.

The researchers said the findings could help scientists understand the neural basis of conditions affecting attention, language, memory, and behaviour.

“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,” Mousley said.