The 5 stages of the brain – ‘adolescent’ period lasts until age 32

There are five key stages of the human brain, a new study has revealed. 

Researchers from the University of Cambridge compared brain scans of 3,802 people aged between 0 and 90.

Their analysis revealed that the average human life is split up by four pivotal ‘turning points’ between five key stages – childhood, adolescence, adulthood, early ageing, and late ageing. 

If you’re in your early 30s and still don’t feel like a proper adult, you’re not wrong, as scientists say the ‘adolescent’ period lasts until age 32.

‘The brain goes through a natural transition around the time puberty begins, which extends until the early 30s,’ lead researcher Dr Alexa Mousley told the Daily Mail.

‘This age window exceeds what many consider “adolescence”.’

According to the researchers, it takes almost three decades of rewiring before our brains reach their adult forms.

Once we reach our mid–30s, our intelligence and personality reach a stable ‘plateau’.

In their study, published in Nature Communications, the researchers used a type of brain scan called an MRI diffusion scan.

These scans look at how water molecules move through the brain to map the neural connections in our brain tissue.

By compiling thousands of scans, they found that our brain’s wiring evolves through five main stages.

Between the ages of zero and nine, we are in the ‘childhood stage’.

During this period, our brains undergo massive reconfiguration and development.

Most importantly, the brain goes through a rapid process called ‘network consolidation’ in which the excess synapses – connections between neurons – are whittled down, with only the most active surviving.

Meanwhile, the outer grey matter and inner white matter expand in volume while the characteristic ridges on the outside of the brain stabilise.

White matter is important for communication within the brain and helps to process information from the senses.

Grey matter, which makes up the outermost layer called the cortex, is responsible for higher-level processes like memory, emotions, and decision-making. 

When we hit around nine years old, the brain starts to undergo its first major turning point, characterised by a ‘step–change’ in cognitive ability.

Between nine and 32 years old, the brain enters a period known as ‘adolescence’.

While the brain’s white matter continues to grow, the biggest changes are happening at the level of the connections between neurons.

During adolescence, the brain’s architecture becomes increasingly refined and efficient.

‘Efficiency in the brain is similar to how you’d think of an efficient path between two places – a short, direct route,’ explains Dr Mousley.

‘When short paths that allow for communication between brain regions form or strengthen, the brain becomes more efficient.’

This era is defined by efficient connections both within specific regions and across the brain as a whole, which is related to enhanced cognitive performance.

The changes reach their peak in the early 30s, which the researchers say is the ‘strongest topological turning point’ of our entire lives.

However, adolescence is also associated with a marked rise in the prevalence of mental health disorders.

Senior author Professor Duncan Astle says: ‘Many neurodevelopmental, mental health and neurological conditions are linked to the way the brain is wired.

‘Indeed, differences in brain wiring predict difficulties with attention, language, memory, and a whole host of different behaviours.’

However, the researchers say the exact mechanisms behind this connection require more investigation.

From around 32 to 66, we enter ‘adulthood’ – the longest of all the brain’s eras.

During this time, our brains stop becoming more efficient, and the structure stabilises with more ‘segregation’ emerging as regions start to become more compartmentalised.

Based on previous studies, the researchers say that this corresponds with a ‘plateau in intelligence and personality’, although the reasons for this change aren’t entirely clear.

From the age of 66, the human brain enters the stage of ‘early ageing’, which is the mildest transition period and is marked by the gradual shift towards reduced connectivity and the degradation of the brain’s white matter.

Dr Mousley adds: ‘This is an age when people face increased risk for a variety of health conditions that can affect the brain, such as hypertension.’

The final epoch for our brains comes when we hit the age of 83 and enter the period known as ‘late ageing’.

This period is marked by a dramatic drop in brain connectivity, during which connectivity across the whole brain declines, and we start to become more reliant on certain regions.

According to the researchers, this increased reliance is a direct consequence of our brain’s losing the connections we developed in adolescence.

‘Imagine you normally take one bus to get to work. If that bus route shuts down, you might need to take two buses instead,’ says Dr Mousley.

‘Suddenly, the stop where you transfer between buses becomes much more important to you than it was when there was a direct route! We think something similar may happen in the ageing brain.

‘As some connections weaken, other regions may become more crucial for communication across the brain.’