Scientists have identified five major phases of human brain development, with four key turning points occurring at around ages nine, 32, 66 and 83, according to a large study of nearly 4,000 brain scans from infancy to old age.
The research found that the brain moves through clear “epochs” rather than developing in a smooth, continuous way:
- Birth to ~9 years: Childhood phase, marked by rapid growth and pruning of neural connections.
- ~9 to ~32 years: Adolescent phase, where brain networks become more efficient and organised.
- ~32 to ~66 years: Adult phase, where brain structure stabilises and becomes more compartmentalised.
- ~66 to ~83 years: Early ageing phase, when connectivity begins to decline.
- 83+ years: Late ageing phase, with further reductions in brain network efficiency.
The biggest structural shift happens around age 32, when the brain enters its most stable, adult-like stage. Researchers believe these transitions may help explain patterns in mental health, cognitive performance and age-related decline.
The findings suggest brain development is shaped by major turning points across the lifespan, rather than steady, gradual change.
