Washington, Aug 26 - 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.