The human brain goes through five major eras of structural changes over a lifetime -- marked by turning points at ages nine, 32, 66 and 83 -- as it rewires to support varied ways of thinking as one grows, matures and ultimately declines, a study has suggested.
Age nine is when communications between brain networks developed since birth transition to the adolescent phase, which then lasts up to age 32, researchers led by those from the UK's University of Cambridge explain.
Early thirties is when the brain's neural wiring shifts into "adult mode" -- the longest era lasting over three decades and marked by a stabilising of the brain's architecture. Age 32 is also the "strongest topological turning point" of the entire lifetime, they said.
Age 66 was found to signal the start of an "early ageing", and age 83 that of a "late ageing" stage of brain structure.
The findings published in the journal Nature Communications "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," lead researcher Alexa Mousley, a graduate student at the University of Cambridge's cognition and brain sciences unit, said.
"These eras provide important context for what our brains might be best at, or more vulnerable to, at different stages of our lives," Mousley said.
The lead researcher added that the study is the first to identify major phases of how brain wiring changes across a human's lifespan.
"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 Mousley.
The study analysed the brain structure of 3,802 people, aged zero to ninety, using datasets of magnetic resonance imaging (MRI) diffusion scans, in which connections are mapped by tracking how water moves through brain tissue.
"We identified four major topological turning points across the lifespan -- around nine, 32, 66, and 83 years old. These ages defined five major epochs of topological development, each with distinctive age-related changes in topology," the authors wrote.
The childhood era of the brain is defined by "network consolidation" as synapses -- junction between two brain cells or neurons -- overproduced in a baby's brain are whittled down, with the more active ones surviving, the researchers said.
At age nine, the brain is experiencing a step-change in cognitive capacity and an increased risk of mental health disorders, they said.
Communication across the brain's networks is increasingly refined during the adolescence era -- post age nine up to early thirties. White matter continues to grow in volume and efficiency of connections increases, and is related with an enhanced cognitive performance, the team said.
The changes peak in the early thirties and around age 32.
"We see the most directional changes in wiring and largest overall shift in trajectory, compared to all the other turning points," Mousley said.
The adulthood era of the brain is the longest and when brain architecture stabilises -- this corresponds to a plateau in intelligence and personality based on findings from previous studies, the researchers said.
'Segregation', where brain regions start to become more compartmentalised, was found to be more noticeable during the adulthood era.
The turning point at age 66 was described as "far milder" -- no major structural shift was noted -- despite seeing meaningful changes to patterns in brain networks.
"This is probably related to ageing, with (a) 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," Mousley said.
Age 83 is when the brain enters the final era -- defined by how connectivity across the brain declines further, accompanied by an increased reliance on certain regions, the researchers said.
"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," senior author Duncan Astle, professor of neuroinformatics at the University of Cambridge, said.
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