Scientists identify five distinct ages of the human brain

By Stephen Beech

Five distinct ages of the human brain have been identified.

Four major turning points - around age nine, 32, 66 and 83 - create five broad eras of neural wiring over the average human lifespan, scientists say.

The research team explained that typical adolescent brain development lasts until our early thirties on average, when the adult era of neural wiring finally emerges.

Now, neuroscientists at the University of Cambridge have identified five “major epochs” of brain structure over the course of a human life, as our brains rewire to support different ways of thinking while we grow, mature, and ultimately decline.

The study compared the brains of 3,802 people between zero and 90-years-old using MRI diffusion scans, which map neural connections by tracking how water molecules move through brain tissue.

The scientists say the study, published in the journal Nature Communications, detected five broad phases of brain structure in the average human life, split up by four pivotal “turning points” between birth and death when our brains reconfigure.

The team explained that childhood brain “topology” runs from birth until a turning point at the age of nine, when it transitions to the adolescent phase – an era that lasts, on average, up to the age of 32.

Our early thirties see the brain’s neural wiring shift into adult mode - the longest era, which lasts over three decades.

A third turning point around age 66 marks the start of an “early aging” phase of brain architecture, before the “late aging” brain takes shape at around 83-years-old.

Dr. Alexa Mousley, a Gates Cambridge Scholar who led the research, said: “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.

(Dr. Alexa Mousley, University of Cambridge via SWNS)

“This study is the first to identify major phases of brain wiring across a human lifespan.

“These eras provide important context for what our brains might be best at, or more vulnerable to, at different stages of our lives.

"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.”

She explained that, from infancy through childhood, our brains are defined by “network consolidation”, as the wealth of synapses – the connectors between neurons – overproduced in a baby’s brain are whittled down, with the more active ones surviving.

Across the whole brain, connections rewire in the same pattern from birth until around 9-years-old.

Meanwhile, gray and white matter grow rapidly in volume, so that cortical thickness – the distance between outer gray matter and inner white matter – reaches a peak, and "cortical folding" - the characteristic ridges on the outer brain - stabilizes.

By the first turning point at age nine, the brain is experiencing a step-change in cognitive capacity, as well as an increased risk of mental health disorders.

The second “epoch” of the brain, the adolescence era, sees white matter continue to grow in volume, so organization of the brain’s communications networks is increasingly refined, as measured by the diffusion of water in the scans.

Dr. Mousley says the era is defined by the efficiency of connections both within specific regions as well as rapid communication right across the whole brain, which is related to enhanced cognitive performance.

She said: “Neural efficiency is as you might imagine, well connected by short paths, and the adolescent era is the only one in which this efficiency is increasing."

The researchers say the developments peak in the early thirties, on average, which is the “strongest topological turning point” of the entire lifespan.

Dr. Mousley said: “Around the age of 32, we see the most directional changes in wiring and the largest overall shift in trajectory, compared to all the other turning points.

“While puberty offers a clear start, the end of adolescence is much harder to pin down scientifically.

"Based purely on neural architecture, we found that adolescent-like changes in brain structure end around the early thirties.”

She says, at age 32, brain architecture stabilizes compared to previous phases – with no major turning points for 30 years.

That corresponds with a “plateau in intelligence and personality” based on other studies, according to the research team.

They also found that “segregation” is more noticeable during the adult epoch, as regions slowly start to become more compartmentalized.

The turning point at age 66 is far milder, and not defined by any major structural shifts, although the researchers still found meaningful changes to the pattern of brain networks on average at around that age.

Dr. Mousley said: “The data suggest that a gradual reorganization of brain networks culminates in the mid-sixties.

“This is probably related to aging, with 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.”

The last turning point comes around age 83, and the final brain structure epoch is entered.

While data was relatively limited for that era, the defining feature is a shift from global to local, as whole-brain connectivity declines even further, with increased reliance on certain regions.

Study senior author Dr. Duncan Astle said: “Looking back, many of us feel our lives have been characterized by different phases. It turns out that brains also go through these eras.

“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 behaviors."

He added: “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.”