New Study Reveals Five Key Stages of Brain Development

Scientists say our brains don’t grow in one steady line from childhood to old age. Instead, they move through five clear phases, each with its own major shift in how the brain is wired. This comes from a large

study led by neuroscientists at the University of Cambridge, who analysed MRI scans from almost 4,000 people between infancy and age 90. By watching how water moves through brain tissue, they were able to track how neural connections change over time.What stood out, surprisingly, was how long “adolescence” actually lasts. Most of us think it ends in our late teens or early twenties, but the study suggests it runs from around age nine all the way to the early thirties. Overall, the research shows the brain is constantly adapting, but not in a calm, linear way – more like bursts of activity and reshaping, especially in the first half of life.According to the researchers, the five main phases are:Childhood (0–9), Adolescence (9–32), Adulthood (32–66), Early ageing (66–83), and Late ageing (83+).Below is a simple breakdown of what happens in each stage.

Childhood (birth to around 9)

In the early years, the brain is busy organising itself. Babies are born with far more synapses than they will eventually need. As children grow, the brain strengthens the connections that are used the most and trims away the rest. This “tidying up” process helps sharpen thinking and learning. By the end of childhood, the brain takes a noticeable leap in ability, but it also becomes more sensitive. The researchers noted that this is the point where the risk of certain mental health conditions begins to rise.

Adolescence (9 to early 30s)

Adolescence, as defined in this study, begins much earlier and ends much later than most of us expect. Throughout this long phase, the brain becomes more efficient, with communication between different regions speeding up and becoming more coordinated. This is what supports more advanced thinking and problem-solving skills. The team found that these changes continue into a person’s early thirties, showing that the brain is still fine-tuning itself well beyond the teenage years.

Adulthood (about 32 to 66)

From the early thirties onwards, the brain enters its most stable period. There are no major shifts like in the earlier phases, and this stage lasts for more than three decades. The Cambridge team also noticed a gradual increase in “segregation” which means different brain areas become slightly more specialised and less interconnected than before.

Early ageing (mid-sixties to early eighties)

Around the mid-sixties, the brain begins to reorganise itself again. This is when white matter – the tissue that supports communication between regions – slowly starts to decline, leading to reduced connectivity. According to the researchers, this is also an age when health problems that can affect the brain, such as high blood pressure, become more common. These factors together shape how the brain functions in this phase.

Late ageing (83 and beyond)

The final stage begins in the early eighties. Here, the brain relies more on local networks rather than broad, high-speed communication across regions. This shift from global to local activity reflects the continued decline in long-range connections. People often depend more on familiar, well-practised thinking patterns at this age, using pathways that have been strengthened over a lifetime.