Brain stages: The human brain appears to pass through five distinct phases over a lifetime, with major turning points around the ages of nine, 32, 66 and 83, according to new research.
Scientists at the University of Cambridge analysed brain scans from around 4,000 people aged from childhood to 90 years. By examining how connections between brain cells change over time, they identified clear stages of development, maturity and ageing rather than a smooth, gradual progression from birth to old age.
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The team found that the brain remains in an extended “adolescent” phase until the early thirties, when its network of connections appears to reach peak efficiency. The findings, published in the journal Nature Communications, could help explain why the risks of mental health problems and dementia rise at particular ages.
Lead author Dr Alexa Mousley said the brain is constantly “rewiring” itself in response to experience, but this does not occur in a straight line. Instead, there are periods of rapid reorganisation and relative stability, punctuated by clear transition points around specific ages.
In early childhood, from birth to about nine years, the brain grows quickly in size but also begins pruning the huge number of connections, or synapses, formed in the first years of life. During this stage, the network is relatively inefficient; information takes less direct routes across different brain regions, rather like a child wandering through a park rather than walking straight from one point to another.
Around the age of nine, the brain enters a dramatic new phase that lasts until roughly 32. During this long window of adolescence and early adulthood, connections between brain cells are refined and reorganised, becoming markedly more efficient. Dr Mousley described this shift as the most profound change across all stages. It also coincides with the period of life when many mental health conditions first emerge.
This extended adolescent phase begins around puberty. Still the study adds to growing evidence that it continues far beyond the teenage years, into the twenties and, based on this work, into the early thirties. According to the researchers, this is the only time in life when the brain’s network becomes more efficient rather than less, supporting previous findings that many aspects of brain function appear to peak in the early thirties.
From about 32 to 66, the brain enters a long adult phase marked by relative stability. Changes in wiring still occur, but at a slower pace than during adolescence. Over these decades, however, the gains in efficiency have gradually started to reverse. Dr Mousley said this period seems to match the plateau many people notice in intelligence and personality measures, with fewer dramatic shifts than in earlier years.
Around the age of 66, the brain moves into what the team call early ageing. Rather than a sudden decline, there is a subtle shift in how different regions communicate. Even though the study focused on healthy volunteers, this is also the age when conditions such as dementia and high blood pressure, which can affect brain health, start to become more common.
The final phase, late ageing, begins at about 83. The patterns seen were essentially an amplification of the earlier ageing phase, with more pronounced separation into distinct functional regions and further reductions in overall network efficiency.
Dr Mousley said she was struck by how closely these brain stages lined up with major life milestones, including puberty, midlife stability, the onset of age-related health problems and the social changes that often come in the early thirties, such as parenthood and career consolidation. She added that individuals will naturally move through each phase at slightly different ages, but the turning points stood out clearly when looking at thousands of scans together.
The study did not separate results for men and women, and the authors noted that future work will need to consider factors such as menopause and sex-specific patterns of ageing.