Washington, Aug 26 (IANS) : Adolescents who engage in dangerous behaviour may be a sign of more mature brains, says a new study.

The brain goes through a course of maturation during adolescence and does not reach its adult form until the mid-twenties.

Emory University neuroscientists used a form of magnetic resonance imaging (MRI), diffusion tensor imaging (DTI) to measure structural changes in brain's white matter and probe the link between high risk taking and cerebral development.

A long-standing theory has assumed that delayed brain maturation triggers impulsive and dangerous decisions in adolescence. The new study calls into question this theory.

"In the past, studies have focussed on the pattern of grey matter density from childhood to early adulthood," says Gregory principal study investigator and professor of psychiatry and neuroeconomics at Emory University.

"We were surprised to discover that risk-taking was associated with more highly-developed white matter -- a more mature brain," says Berns. Both grey and white matter are important for understanding brain function.

Grey matter is the part of the brain made up of neurons, while white matter connects neurons to each other. As the brain matures, white matter becomes denser and more organised. Grey matter and white matter follow different trajectories.

"With new technology, we were able to develop the first study looking at how development of white matter relates to activities in the real world." Berns suggests that doing adult-like activities requires sophisticated skills.

The study enrolled 91 adolescents aged 12 through 18 over a three-year period. DTI was used to measure corresponding structural changes in white matter.

Levels of involvement in risky behaviours were measured by a survey that included questions about the teens' thrill seeking behaviours, reckless behaviours, rebellious behaviours and antisocial behaviours.

"Society is a lot different now than it was 100 years ago when teens were expected to go to work and raise a family," says Berns. "Now, adolescents aren't expected to act like adults until they are in their twenties, when they have finished their education and found a career."

The Centre for Disease Control (CDC) reports that 27,000 people aged between 10 and 24 die from bad decisions in the US alone every year, says an Emory release.