A new study from the University of Cambridge is challenging long-held beliefs about brain progress, revealing it doesn’t occur as a steady progression but rather in five distinct phases throughout life. Researchers, who analyzed MRI scans of nearly 4,000 individuals aged zero to 90, identified key transition points at ages 9, 32, 66, and 83, offering new insights into the complex relationship between brain structure and human behavior. The findings, published this week in Nature, could reshape our understanding of mental health conditions and dementia, potentially leading to earlier and more targeted interventions.
A new study has identified key turning points in brain development that occur throughout a human lifespan, offering potential insights into mental health disorders and dementia.
While it’s long been understood that the brain is constantly changing in response to new knowledge, experiences, and stimuli, this research reveals these changes don’t unfold as a gradual process from birth to death. Instead, the brain undergoes distinct phases of maturation.
“This study highlights the complex and non-linear nature of human development, with unique phases of maturation,” explained researchers from the Medical Research Council (MRC) Cognition and Brain Sciences Unit at Cambridge.
The findings could improve understanding of the processes that contribute to the development of mental health conditions and dementia over the course of a lifetime.
Five Key Transition Points
Researchers compared the brains of 3,802 individuals ranging in age from zero to 90 years old, using data from diffusion magnetic resonance imaging (MRI) scans. These scans mapped neural connections by tracking the movement of water molecules through brain tissue.
Neural connections are bundles of axons that link different neurons, facilitating communication between them. Understanding these connections is crucial for understanding how the brain functions.
The scientists identified five distinct phases in brain development, pinpointing what they call “major transitions” in brain structure throughout life. These transitions occur as the brain’s networks reorganize to support different ways of thinking as we “grow, mature, and eventually decline.”
These phases include childhood (birth to age 9), adolescence (ages 9 to 32), adulthood (ages 32 to 66), early old age (ages 66 to 83), and late old age (age 83 and beyond).
“The brain is constantly rewiring throughout life. There’s always strengthening and weakening of these connections, and it’s not a constant pattern – there are fluctuations and phases of brain reorganization,” said Alexa Mousley, a co-author of the study, to the BBC.
“These eras provide important context for what our brains may be best or most vulnerable at, at different stages of our lives. This could help us understand why some brains develop differently at key points in life, whether it’s with learning difficulties in childhood or dementia in later years,” Mousley explained.
A Shift Occurs at Age 9
The first phase, from birth to age 9, is characterized by rapid brain growth, particularly in the volume of gray matter and internal white matter. This period involves the “consolidation of network connections.” However, around age 9, there’s a reduction in the abundance of connections between brain cells, called synapses, that were created earlier in life.
During this phase, the brain operates less efficiently, exploring possibilities rather than taking a direct route from point A to point B.
At nine years old, everything changes. Connections in the brain shift to “relentless efficiency.” “It’s a big shift, it’s the most profound change between brain phases,” Mousley described.
“Adolescence begins around the onset of puberty, but in brain terms, it ends much later than we assume,” the neuroscience team observed, suggesting it continues into the 20s and even 30s.
“This phase is the only period in the brain where its network of neurons becomes more efficient,” Mousely pointed out.
She added that brain function peaks in the early 30s, but it’s “very interesting” that the brain remains in the same phase between ages nine and 32.
Brain Architecture Stabilizes at 32
At age 32, the longest phase of brain development begins. Called adulthood, this is when the “brain’s architecture stabilizes compared to earlier phases” and remains that way for three decades. This corresponds to a “plateau in intelligence and personality” based on other studies, the scientists say.
They also discovered that “segregation” becomes more noticeable during this stage, as different regions of the brain become increasingly compartmentalized.
Early Aging Begins at 66
The turning point at age 66 is less dramatic than previously thought, not exhibiting a sudden, sharp decline, although researchers did find significant changes in brain network patterns around that age.
“The data suggests a gradual reorganization of brain networks culminates in the mid-60s,” Mousley described.
“This is likely related to aging, with connections becoming further reduced as internal white matter begins to degenerate,” she explained.
“This is an age where people face increased risk of a variety of health conditions that can affect the brain, such as hypertension,” she added.
Late-Life Brain Changes
The final turning point arrives around age 83, marking the beginning of the last era of brain structure.
Although data is limited for this period, this stage is defined by a shift from global to local connections, as brain connectivity further decreases and becomes more reliant on specific regions.
“Looking back, many of us feel that our lives have been characterized by different phases. It turns out brains go through these eras too,” added co-author Duncan Astle, Professor of Neuroinformatics at Cambridge.
“Many neurodevelopmental, mental health, and neurological conditions are linked to how the brain assumes connections. In fact, differences in the structure of brain connections – which is crucial for information processing, thinking, movement, and learning – foreshadow difficulties with attention, language, memory, and a whole range of different behaviors,” he argued.
“Understanding that the brain’s structural journey isn’t one of constant progression, but rather one of key turning points, will help us identify when and how its network connections are vulnerable to disruption,” Astle concluded.
The research, published in Nature this week, was supported by the Medical Research Council, the Gates Foundation, and the Templeton World Charitable Foundation.
