Study identifies five major stages of brain growth, claims adulthood actually starts at 32

Childhood phase: The researchers found that the earliest years involved rapid expansion in brain size while simultaneously reducing the initial excess of synapses formed in infancy. This period was described as one of inefficient functioning, with the brain following an unfocused pattern of communication rather than streamlined processing.

Adolescence phase (Nine to 32): At around nine years of age, the team observed a sharp transition. Dr Mousley referred to this shift as significant, describing it as “a huge shift” and the most dramatic boundary between stages. Neural pathways became more efficient during this period than at any other time in the lifespan. She noted that the data supported existing knowledge that the brain’s performance typically peaks in the early thirties. She also said it was “very interesting” that the adolescent phase lasted from nine through to 32, an interval that aligned with but extended beyond typical understandings of puberty and post-teen development.

This same period represented the lifetime window in which the risk of many mental health disorders first increased.

Adulthood phase (32 to 66): From 32 onwards, the researchers observed a long interval in which neural change was slower. Dr Mousley said the findings “align with a plateau of intelligence and personality”, a pattern that many people recognised in themselves or others.

Early ageing phase (66 to 83): The shift at around 66 did not resemble a sudden collapse but indicated a change in how the brain’s networks operated. Rather than working as one integrated system, the researchers found that the brain began splitting into more distinct functional regions, as though areas were starting to work in separate clusters. Although the study focused on healthy individuals, this was also the age at which dementia and conditions such as high blood pressure—which affect cognitive health—began to appear more frequently.

Late ageing phase (83 Onwards): A final change occurred at around 83. The researchers noted that fewer healthy individuals were available for scanning in this age range, but the patterns they did observe showed an intensified version of the early-ageing shifts. Dr Mousley said she was struck by how closely the age markers reflected both biological events such as puberty and later-life medical concerns, as well as broader life changes that commonly occur in early adulthood.

The study did not analyse men and women separately, and the researchers acknowledged that factors such as menopause would need further investigation.

Prof Duncan Astle, a co-author from Cambridge, said, “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 behaviours.”

Prof Tara Spires-Jones, director of the Centre for Discovery Brain Sciences at the University of Edinburgh, who was not involved in the work, said, “This is a very cool study highlighting how much our brains change over our lifetimes.” She said the results were consistent with current understanding of how brain networks aged, although she emphasised that “not everyone will experience these network changes at exactly the same ages.”