Researchers at the University of Washington have been using magnetic resonance imaging (MRI) scans to look at how the brains of adolescent boys with attention deficit hyperactivity disorder (ADHD) and conduct disorder (bad behaviour) work. They compared 19 boys with one or both of the disorders to 11 ones who were unaffected. The boys were asked to press a button when a light flashed in order to earn money. In certain parts of the trial the payouts stopped although the boys were told that they would start again in a bit. Both groups of boys performed equally well and both groups showed equal activity in a region of the brain called the striatum, which is associated with reward. In the unaffected boys, when the rewards stopped a part of the brain called the anterior cingulate became active damping down the link between pressing the button and the reward in a process psychologists call extinction. However, in the boys with ADHD and conduct disorder the anterior cingulate failed to become active and the striatum maintained its activity even when the payouts had stopped. Put more simply the boys with ADHD and conduct disorder's brains still expected to get a reward when none was on offer, something that might shed light on the higher levels of impulsivity, risk-taking and pleasure-seeking found in children with these conditions.
You can find out more about this research at