Patients with attention deficit hyperactivity disorder (ADHD) can be quite impulsive, restless and easily distracted. In short, they often have difficulty controlling their behavior. Diminished behavioural control can result in problems at work or in someone’s social life. Although patients with ADHD often find it hard to focus at work, some can spend hours playing computer games without facing distraction. In other words, patients with ADHD appear able to control their behavior much better when they are doing something enjoyable or rewarding rather than boring.
Previous studies showed that patients with ADHD can indeed exert more control when expecting a reward (e.g. money). We wanted to study the possibility that the effect of rewards on control is different in the brains of ADHD patients.
Whether someone is at risk for developing ADHD is partly genetically determined. We studied adults with ADHD who carry a variant of a gene that has been associated with ADHD (a risk gene), and compared these patients with a group of patients carrying another (non-risk) variant of that gene.
We used functional MRI to measure brain activity in adults with ADHD while they performed a task that required the exertion of control for which they could earn money. When subjects had not taken their medication (e.g. Ritalin), we observed abnormal brain activity in the ADHD group with the risk gene compared with comparable subjects without ADHD during the control task with reward. We also looked at brain responses when patients with ADHD did take their medication. As expected we observed that medication normalized the abnormal brain activity.
These results suggest a difference in the way the brains of patients with ADHD use information about rewards in relation to behavioral control. Deficits in exerting control in ADHD could, at least partly, be due to changes in the way the brain processes rewards.
Read the full article here.