Image copyright University of Cambridge Image caption Areas with many attachments to other parts of the brain develop fast in teenagers

A University of Cambridge team has identified the areas of the brain that change the most during the teenage years.

Brain scans showed that they are the areas associated with complex thought processes.

The scientists also discovered a link between teenage brain development and mental illness, such as schizophrenia.

The research is published in the Proceedings of the National Academy of Science.

The team from Cambridge's department of psychiatry scanned the brains of 300 people between the ages of 14 and 24.

While the areas associated with the basic functioning of the body such as vision, hearing and movement are fully developed by adolescence, the areas associated with complex thought and decision making are still changing.

These areas are nerve centres with lots of connections to and from other key areas.

You can think of the brain as a global airline network that's made up of small infrequently used airports and huge hubs like Heathrow where there is very high traffic.

The brain uses a similar set up to co-ordinate our thoughts and actions.

During adolescence, this network of big hubs is consolidated and strengthened. It's a bit like how Heathrow or JFK have become gradually busier over the years.

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The researchers then looked at the genes involved in the development of these brain "hubs" and found that they were similar to those associated with many mental illnesses, including schizophrenia.

The discovery is in line with the observation that many mental disorders develop during adolescence, according to researcher Dr Kirstie Whitaker.

"We have shown a pathway from the biology of cells in the area through to how people who are in their late teenage years might then have their first episode of psychosis," she told the BBC.

Many studies have shown that, in addition to genetics, stress during childhood and the teenage years is linked to mental illness.

The new findings indicate that maltreatment, abuse and neglect may well continue to disrupt the development of the higher brain functions during the crucial teenage years and so contribute to the emergence of mental illness.

Symptoms of schizophrenia:

Delusions

Difficulty thinking

Feeling as though body is controlled by someone else.

Hallucinations

Loss of interest, energy and emotions

Lead researcher Prof Ed Bullmore, whose work was funded by the Wellcome Trust, believes the discovery of a biological link between teenage brain development and the onset of mental illness might help researchers identify those most at risk of becoming ill.

"As we understand more about what puts people at risk for schizophrenia, that gives us an opportunity to try to identify individuals that are at risk of becoming schizophrenic in the forseeable future, the next two to three years, and perhaps to offer some treatment then that could be helpful in preventing the onset of clinical symptoms. "

The study also sheds light on the mood and behavioural changes experienced by teenagers during normal brain development.

"The regions that are changing most are those associated with complex behaviour and decision making," says Dr Whitaker.

"It shows that teenagers are on a journey of becoming an adult and becoming someone who is able to pull together all these bits of information.

"This is a really important stage to go through. You wouldn't want to be a child all your life.

"This is a powerful and important stage that you have to go through to be the best and the most capable adult that you can be."