A new British study shows for the first time that emotional centres of the brain are strikingly stunted in boys with conduct disorder (CD), even when the problems first appear in adolescence.
Conduct disorder is a recognised psychiatric condition characterised by aggression and antisocial behaviour.
It affects about 5 per cent of school-age children and involves classic “yob” behaviour such as acts of violence, fighting, weapon use, pathological lying, thieving and breaking into homes.
Rates of CD have increased sharply around the world since the 1950s. The condition can develop in young children, or not show itself until the teenage years.
Those affected by the condition are at greater risk of mental problems, substance abuse and criminality in later life.
It has long been thought that adolescent-onset CD is merely the result of susceptible teenagers imitating badly-behaved peers. But the new research challenges this view, pointing to brain changes that affect all youngsters with the condition.
The highlighted brain areas are the amygdala and insula, which contribute to emotional perception, empathy, and the ability to recognise when others are in distress. Magnetic resonance imaging (MRI) brain scans showed both regions were significantly smaller in affected teenagers, including those who only became badly behaved in adolescence.
Sophisticated computer processing was used to identify the differences, and revealed that insula volume reduced with the severity of behavioural problems.
The scientists are cautious about how to interpret the findings, published in the American Journal of Psychiatry online.
But they point out there is already evidence of links between conduct disorder and home environment.
Professor Ian Goodyer, one of the researchers from Cambridge University, said at a news conference in London: “I don’t think there’s any doubt in anyone’s mind that there are significant environment antecedents in virtually all cases of conduct disorder.
“Almost always there is some degree of early family adversity.”
This came under the broad heading of “impaired parenting”, especially with regard to the emotional environment, he said.
Social and sexual abuse may be contributing factors.