Image caption Brain scans showed significant differences

The brains of teenage girls with behavioural disorders are different to those of their peers, UK researchers have found.

The Journal of Child Psychology and Psychiatry study of 40 girls revealed differences in the structure of areas linked to empathy and emotions.

Previous work has found similar results in boys.

Experts suggest it may be possible to use scans to spot problems early, then offer social or psychological help.

An estimated five in every 100 teenagers in the UK are classed as having a conduct disorder.

It is a psychiatric condition which leads people to behave in aggressive and anti-social ways, and which can increase the risk of mental and physical health problems in adulthood.

Rates have risen significantly among adolescent girls in recent years, while levels in males have remained about the same.

Fear detector

In this study, funded by the Wellcome Trust and Medical Research Council, UK and Italian researchers conducted brain scans of 22 teenage girls who had conduct disorder and compared them with scans of 20 who did not.

It would be possible to use scans where a person is at high risk of offending in the future Dr Graeme Fairchild,, Researcher

They also checked the scans against others previously taken of teenage boys with conduct disorder.

The team found part of the brain called the amygdala was smaller in the brains of male and female teenagers with conduct disorder than in their peers.

The amygdala is involved in picking up whether or not others feel afraid - and plays a role in people feeling fear themselves.

Girls with conduct disorder also had less grey matter in an area of the brain called the insula - linked to emotion and understanding your own emotions.

However the same area was larger in boys with conduct disorder than healthy peers, and researchers are not yet sure why that is the case.

The brains of those with the worst behaviour were most different from the norm.

Biological basis

Dr Andy Calder, from the MRC cognition and brain sciences unit, who worked on the study, said: "The origins of these changes could be due to being born with a particular brain dysfunction or it could be due to exposure to adverse environments such as a distressing experience early in life that could have an impact on the way the brain develops."

Dr Graeme Fairchild, of the University of Cambridge who also worked on the study, said there were potential uses for the finding.

"In the US, people are already using brain scans to argue diminished responsibility. I think we're too early in our understanding to really do that, but it is happening.

"It would also be possible to use scans where a person is at high risk of offending in the future.

"More help could be given to the family and, in the same way that someone with language impairment receives extra help, help could be given to teach a person to understand emotions - and the emotions of others - better."

Dr Michael Craig of King's College London's Institute of Psychiatry, who is also looking at using scans to pick up early signs of conditions such as anti-social behaviour, autism and attention deficit-hyperactivity disorder (ADHD), said: "The important thing is that in the studies to date there has been an absence of research looking at females, so this work is an important first step.

"And it suggests that at least a component of this has a biological basis - and there are people who don't believe there is one."