Scientists have identified five major “eras” of human brain development in one of the most comprehensive studies to date of how neural wiring changes from infancy to old age.
The study, based on brain scans of nearly 4,000 people aged between one and 90, explored neural connections and how they develop over the course of our lives. This revealed five broad stages, divided by four critical “turning points” in which brain organization moves on a different trajectory at around ages nine, 32, 66 and 83.
“Looking back, many of us think of our lives as having had different stages. It turns out that the brain also goes through these eras,” said Professor Duncan Astle, a neuroinformatics researcher at the University of Cambridge and senior author of the study.
“Understanding that the brain’s structural journey is not a question of steady progress, but rather of a few major turning points, will help us identify when and how its wiring is sensitive to disruption.”
The childhood period of development is found from birth to the age of nine, when it transitions to the adolescent stage – an era that lasts on average until the age of 32.
The brain’s neural wiring shifts into adult mode in a person’s early 30s—the longest age, lasting more than three decades. The third turning point around age 66 marks the beginning of the “early aging” phase of brain architecture. Ultimately, the “late aging” brain takes shape around age 83.
The scientists quantified brain organization using 12 different measurements, including the efficiency of the wiring, how divided it is and whether the brain relies heavily on central hubs or has more dispersed connectivity networks.
From infancy through childhood, our brains are defined by “network consolidation,” as the wealth of synapses – connectors between neurons – in a child’s brain are reduced, and the more active the more active. The study found that the efficiency of the brain’s wiring decreases during this period.
Meanwhile, the volume of gray and white matter increases rapidly, causing cortical thickness – the distance between the outer gray matter and the inner white matter – to reach a peak, and cortical folding, the distinctive ridges on the outer brain, become stable.
In the second “age” of the brain, the age of adolescence, white matter continues to increase in volume, so the organization of the brain’s communication networks is becoming increasingly sophisticated. This era is defined by the steadily increasing efficiency of connections throughout the brain, which is related to improved cognitive performance. Epochs were defined by the brain remaining on a constant trend of development over a sustained period of time rather than remaining in a fixed state throughout time.
“We’re certainly not saying that people in their late 20s will behave like teenagers, or even that their brains look like teenagers,” said Alexa Mousley, who led the research. “It’s really a pattern of change.”
He said the findings could provide information about risk factors for mental health disorders, which often emerge during adolescence.
The strongest overall change in trajectory is seen at approximately age 32. Life events such as becoming a parent may play a role in some of the changes observed, although research has not explicitly tested this. “We know that in women who give birth, their brains change afterward,” Moussali said. “It is reasonable to assume that there may be a connection between these milestones and what is happening in the brain.”
By the age of 32, brain structure appears to be stable compared to previous stages, which is consistent with a “plateau in intelligence and personality” based on other studies. Brain regions also become more divided.
The last two endpoints were defined by a decrease in brain connectivity, which was thought to be related to aging and degeneration of white matter in the brain.
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