Neuroscientists at the University of Cambridge argue in a new study that the human brain undergoes five phases of reorganization throughout a person’s lifetime, which the researchers refer to as “five epochs.” The most intriguing finding is that the adolescent epoch may last until the age of 30.
The study, conducted by Cambridge’s MRC Cognition and Brain Sciences Unit, shows that the human brain reorganizes itself to support different modes of thinking as we grow older, mature, and eventually decline. The researchers compared the brains of 3,802 people aged from zero to ninety using MRI datasets that map neural connections by tracking how water molecules move through brain tissue.
In the study, published in Nature Communications, the scientists report that they identified five broad phases of brain structure in the average person, separated by four key “turning points” between birth and death as the brain remodels itself. The “topology” of the child’s brain extends from birth to a turning point at age nine, when it begins to move into the adolescent phase, an epoch that on average lasts until age thirty-two.
Adulthood
In the early thirties, the brain’s neural wiring transitions into the adult phase. This is the longest epoch, lasting for more than three decades. A third turning point around age sixty-six marks the beginning of the “early aging” phase. Finally, the “late aging” brain takes shape at around eighty-three.
“We know that the brain’s wiring is vital to our development, but we don’t have a complete picture of how it changes throughout life and why. This study is the first to identify major phases of brain wiring across the human lifespan. These epochs provide important context for what our brains may do best — or be most vulnerable to — at different life stages. It may help us understand why some brains develop differently at key moments, whether in childhood learning difficulties or dementia in old age,” says Dr. Alexa Mousley, who led the research.
The child brain
From infancy to childhood, the brain is characterized by “network concentration,” as the excess of synapses produced in the infant brain is reduced, with the most active ones surviving. Throughout the brain, connections are remodeled in the same pattern from birth until about age nine.
At the same time, gray matter and white matter increase rapidly so that cortical thickness reaches its maximum, while the folding of the cerebral cortex stabilizes. At the first turning point, age nine, the brain undergoes a sharp shift in cognitive capacity as well as an increased risk of mental-health disorders.
The adolescent brain
The second “epoch,” adolescence, is marked by continued growth in white matter, as the organization of the brain’s communication networks becomes increasingly refined, as measured by water diffusion in imaging. This epoch is characterized by growing efficiency of connections both within specific regions and across the brain, which is linked to improved cognitive function.
“Neural efficiency is, as one might imagine, about well-connected and short pathways, and adolescence is the only epoch during which this efficiency increases,” says Mousley. These developments peak in the early thirties on average, which the researchers describe as the “strongest topological turning point” across the lifespan.
“Around age thirty-two, we observe the most pronounced changes in wiring and the greatest overall shift in developmental trajectory compared to all other turning points,” said Mousley. “While adolescence has a clear starting point, its end is difficult to define scientifically. Based solely on neural architecture, we found that adolescent-type structural changes in the brain conclude roughly in the early thirties.”
Stabilization
At age thirty-two, the longest epoch — adulthood — begins. Brain architecture stabilizes compared to earlier phases, with no major turning points for the next thirty years. This corresponds to a “stabilization of intelligence and personality,” according to other studies.
The researchers also found that “segregation” is most pronounced during this epoch, as brain regions gradually become more distinct from one another.
Early-aging brain
The turning point at age sixty-six is milder and is not marked by major structural alterations, although the researchers identified significant shifts in brain-network patterns around this age.
“The data suggest that a gradual reorganization of brain networks peaks in the mid-sixties. This is likely related to aging, with further reductions in connectivity as white matter begins to degenerate. This is the age when people face increased risk for various conditions that may affect the brain, such as hypertension,” says Mousley.
The aging brain
The final turning point appears around age eighty-three, when the brain enters the last phase of its structural life. Although the available data are limited, the key characteristic is a shift from global to local connectivity, as overall connectivity declines further and reliance on specific regions increases.
“Looking back, many of us feel that our lives have been defined by different phases. It turns out the same is true for the brain. Many neurodevelopmental, psychiatric, and neurological conditions are linked to the way the brain is wired. Differences in brain wiring predict difficulties in attention, language, memory, and a range of other behaviors.
Recognizing that the journey of brain structure is not a gradual path but a series of a few major turning points will help us identify when and how wiring is vulnerable to disorders,” explains Duncan Astle, professor of neuroinformatics at Cambridge. The research was supported by the Medical Research Council, the Gates Foundation, and the Templeton World Charitable Foundation.