A new study says that malfunctioning brains are to be blamed for antisocial behaviour such as drug abuse, breaking laws, and reckless attitude in boys.
"Brain responses to everyday rewards and punishments gradually guide most youngsters' decisions to conform with society's rules. However, when these seriously troubled kids experience rewards and punishments, and make decisions, their brains apparently malfunction," said Thomas Crowley, lead author on the study.
"Our findings strongly suggest that brain malfunction underlies their frequent failure to conform to rules, to make wise decisions, and to avoid relapses back to drug use and antisocial acts," he said.
Researchers at the University of Colorado School of Medicine and the University of Maryland, studied 20 adolescent boys.
On average they had been on probation 139 of the last 180 days; 19 of the 20 had the psychiatric diagnosis of conduct disorder, and all had diagnoses of substance use disorder.
They had been abstinent, however, an average of about five weeks when studied. They were compared with 20 other boys who did not have serious antisocial or drug problems, but who were of similar age, ethnicity, and home neighbourhoods.
All played a computerized risk-taking game that repeatedly presented a choice between a cautious and a risky behaviour: press the left button and always win one cent, or press the right button and either win five cents or lose ten cents.
The scientists examined brain activation with functional magnetic resonance imaging (fMRI) as the boys decided to press right or left, and then as they experienced wins or losses after right presses.
Brain activation differed dramatically in the two groups.
During decision-making, antisocial boys had significantly less brain activity than normal in both of those regions, and also in other decision-making areas (orbitofrontal cortex, amygdala, insula).
Altogether, during decision-making about 6000 voxels (a voxel is a tiny cube in the brain) activated significantly less in antisocial boys than in comparison boys. No voxels activated more in antisocial boys. Such under-activity during decision-making could contribute to disinhibited antisocial and drug-using behaviours.
The antisocial boys also had dysphoria, a chronic sad-anxious state, with "reward insensitivity"; in the game their brains responded less than the comparison boys' brains to wins.
They also had "punishment hypersensitivity", with greater brain response to losses than comparison boys.