The brains of some aggressive and antisocial teenage boys look different than those of normal teenagers, British researchers have found.

Conduct disorder is psychiatric condition characterized by higher than normal levels of aggressive and antisocial behaviour. It can develop in childhood or in adolescence and affects about five out of every 100 teenagers in the U.K., researchers say.

People affected by conduct disorder run a greater risk of further mental and physical health problems in adulthood.

The new brain scan findings published in Friday's online issue of the American Journal of Psychiatry suggest adolescents who develop conduct disorder have differences in their brain and are not merely imitating misbehaving peers.

"Changes in grey matter volume in these areas of the brain could explain why teenagers with conduct disorder have difficulties in recognizing emotions in others. Further studies are now needed to investigate whether these changes in brain structure are a cause or a consequence of the disorder," said Prof. Ian Goodyer of the University of Cambridge.

For the study, scientists used MRIs to look at the brains of 65 teenage boys with conduct disorder and 27 healthy teenage boys.

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The volume of the insula, in yellow, was smallest in those with the most severe behaviour problems. (University of Cambridge)

They found that two regions of the brain, the amygdala and the insula, both regions that  govern emotion perception and empathy, were much smaller in the brains of the teenagers with conduct disorder.

The changes were found in both the childhood and adolescent forms of the disorder.

The volume of the insula was smallest in those with the most severe behaviour problems.

Goodyer and his co-authors called the paper the largest structural neuroimaging to date to investigate antisocial behaviour in this way.

They cautioned that while the results support developmental theories that link amygdala dysfunction with antisocial behaviour, more research is needed to tell whether the defects are a cause or consequence of conduct disorder.