Researchers at University of Washington have discovered a brain abnormality linked to attention deficit hyperactivity and conduct disorders (ADHD) in boys.
During the study, the researchers focused on two brain areas-the striatum and anterior cingulate cortex.
The striatal region is a network of structures in the mid brain that motivates people to engage in pleasurable or rewarding behaviour.
The anterior cingulate is higher in the brain, and normally activates when an expected reward stops.
Theodore Beauchaine, a UW associate professor of psychology and senior author of the paper, says that this process doesn't occur, at least as quickly, in boys with attention deficit hyperactivity or conduct disorders.
"When children engage in impulsive behaviour they are looking to stimulate themselves and have fun," said Beauchaine.
"Children with attention deficit hyperactivity disorder are always looking to have fun and that is what gets them in trouble," he added.
But even when you stop the reward for children with these disorders, they continue to focus on the reward long afterward and the anterior cingulate does not appear to become activated.
For the study, the researchers compared 19 boys with either or both disorders and 11 normally developing boys. The adolescents ranged in age from 12 to 16.
They were asked to play a simple game that sometimes gave them a monetary reward for correct answers.
Beauchaine said that there was no difference in the accuracy or speed - the behavioral response - between the two groups. But there was a difference in brain activation.
"This shows there is an abnormality, but not in the place we expected to find it. We expected to find a difference in the way the striatum functions, but instead found it in anterior cingulate functioning," he said.