Scientists have identified five major stages of human brain development, with key turning points occurring around the ages of 9, 32, 66 and 83, according to a large new study.
The research, based on brain scans from nearly 4,000 people ranging from infancy to age 90, shows that brain development does not happen gradually over time but instead shifts through distinct “epochs” with major changes in structure and connectivity.
The five phases are:
- Childhood: from birth to about age 9
- Adolescence: from around 9 to 32
- Adulthood: beginning at about 32 and lasting for more than three decades
- Early ageing: starting near age 66
- Late ageing: beginning around age 83
During childhood, the brain undergoes “network consolidation,” where excess neural connections are trimmed and more useful ones are strengthened. Although grey and white matter grow rapidly during this time, the overall efficiency of brain wiring actually decreases.
In the adolescent phase, white matter continues to grow and brain networks become more refined. Connectivity efficiency steadily improves, which is linked to better thinking and cognitive performance. Researchers say this period is also when many mental health conditions begin to emerge.
The biggest structural shift happens around age 32, when the brain moves into its longest-lasting adult phase. During this period, brain organisation stabilises, and regions become more compartmentalised. This phase is linked to relative stability in intelligence and personality.
From around age 66, and more markedly after 83, brain connectivity begins to decline, likely reflecting age-related changes and degeneration in white matter.
Researchers say understanding these key phases could help identify when the brain is most vulnerable to disruption and improve understanding of mental health and neurological conditions.
