New research from the University of Cambridge has revealed that the human brain goes through five distinct phases in life, with major turning points at ages nine, 32, 66, and 83.

The findings, published in Nature Communications, offer fresh insights into how the brain evolves and why the risk of mental health disorders and dementia varies over a lifetime.

The study analyzed brain scans from around 4,000 people up to the age of 90 to map the connections between neurons. Researchers found that brain development is not a smooth, continuous process but occurs in distinct stages.

The Five Phases of Brain Development

Childhood (birth to age nine): The brain rapidly grows in size but also prunes excess neural connections, or synapses. During this period, the brain operates inefficiently, akin to a child meandering through a park rather than taking the most direct route.

Adolescence (ages nine to 32): Beginning at age nine, the brain undergoes a period of heightened efficiency, reorganizing its connections in a “ruthless” pruning process. This stage, which lasts into the early 30s, is also when individuals face the highest risk of developing mental health disorders. Researchers note that adolescence extends far beyond the teenage years, peaking in early adulthood.

Adulthood (ages 32 to 66): This is the longest phase, marked by stability and a gradual reversal of the efficiency gains made during adolescence. Cognitive performance and personality traits typically plateau during this period.

Early Ageing (ages 66 to 83): At 66, the brain begins to reorganize into more tightly connected regions rather than functioning as a fully integrated network. Although the study focused on healthy brains, this stage often coincides with the onset of dementia and other age-related health conditions.

Late Ageing (83+): The final phase shows even more pronounced changes in brain connectivity. Researchers faced challenges in studying this age group due to the scarcity of healthy brains available for scanning.

Dr. Alexa Mousley, the lead author, said: “The brain rewires across the lifespan. It’s always strengthening and weakening connections, and it’s not one steady pattern — there are fluctuations and phases of brain rewiring.” She added that the alignment of these phases with key life milestones, such as puberty, early parenthood, and late-life health issues, was particularly striking.

Professor Duncan Astle, part of the Cambridge research team, emphasized the importance of the findings for understanding neurodevelopmental, mental health, and neurological conditions. “Differences in brain wiring predict difficulties with attention, language, memory, and a host of behaviours,” he explained.

Professor Tara Spires-Jones from the University of Edinburgh, who was not involved in the study, described it as “a very cool study highlighting how much our brains change over our lifetimes.” She noted that while the results are consistent with existing knowledge on brain ageing, individual variations mean not everyone will experience these network changes at the same ages.

This research provides a comprehensive roadmap of brain development and ageing, offering potential clues for the timing of interventions to support mental health and cognitive function throughout life. (ILKHA)