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Brain undergoes five key phases with turning points at 9, 32, 66 and 83
New research from the University of Cambridge identifies five distinct stages in human brain development, each marked by shifts in neural connectivity. The study, published in Nature Communications, analyzed scans from nearly 4,000 individuals up to age 90, revealing critical transitions at ages nine, 32, 66, and 83-periods when the brain's wiring patterns undergo significant reorganization.
Childhood: Rapid growth and inefficient networks
The first phase spans early childhood, characterized by rapid brain expansion alongside the pruning of excess synaptic connections formed in infancy. During this stage, neural activity resembles "a child wandering aimlessly in a park," according to Dr. Alexa Mousley, as the brain prioritizes exploration over efficiency. The transition out of this phase begins abruptly at age nine.
Adolescence: A surge in efficiency and vulnerability
From age nine to 32, the brain enters its most efficient phase, optimizing neural pathways with "ruthless precision," as described by Dr. Mousley. This period-far longer than previously assumed-aligns with heightened risks for mental health disorders. The findings challenge traditional views of adolescence ending in the late teens, instead extending it into the early 30s, when cognitive performance typically peaks.
"It's striking how these ages align with major life milestones-puberty, career shifts, even parenthood in the early 30s," noted Dr. Mousley.
Adulthood: Stability and subtle decline
The third phase, spanning ages 32 to 66, marks a period of relative stability. While changes slow compared to earlier stages, the brain's efficiency begins a gradual decline. Researchers link this to observed plateaus in intelligence and personality traits during middle age. The study suggests this phase reflects a "long, slow unraveling" of the brain's integrated networks.
Early and late ageing: Fragmentation and regional isolation
At 66, the brain enters "early ageing," where global coordination weakens, and regions begin operating more independently-"like band members pursuing solo projects," per the study's analogy. This shift coincides with the onset of dementia and hypertension risks. By age 83, the final phase exhibits even more pronounced fragmentation, though data for this group was limited due to fewer healthy participants.
Implications for health and research
Experts emphasize that while the study provides a "cool" framework for understanding lifelong brain changes (per Prof. Tara Spires-Jones of the University of Edinburgh), individual variability exists. The findings could inform research on neurodevelopmental disorders, mental health, and age-related cognitive decline. Prof. Duncan Astle of Cambridge highlighted the link between brain wiring and conditions affecting attention, memory, and behavior.
Note: The study did not differentiate by sex, leaving open questions about hormonal influences like menopause.
