Until recently, the problems with attention and hyperactivity experienced by people with Attention Deficit Hyperactivity Disorder (ADHD) were thought to be caused by dysregulation of dopamine, which is a chemical in the brain that is involved in processes such as reward-driven behaviour and controlling movement. A new study conducted by researchers working in the BCNI, led by Dr. Natalia del Campo, has shown that this may not be the case, because the drug Ritalin (or methylphenidate) was found to increase the amount of dopamine in the brain of both people with ADHD and healthy volunteers without the disorder. The study has been published in the November issue of Brain.
This double-blind placebo-controlled trial represents a significant step forwards in identifying the causes of ADHD, and may therefore inform future treatments for the disorder. Methylphenidate is currently the drug of choice for treating the symptoms of ADHD and was thought to work by increasing the amount of dopamine available in the brain. By using positron emission tomography (PET) and magnetic resonance imaging (MRI) this study showed that although people with ADHD performed worse overall on a task of attention than healthy volunteers without the disorder, both groups experienced similar increases in dopamine levels after taking Ritalin.
Furthermore, both groups had similar numbers of dopamine receptors in an area of the brain known as the striatum, an area that is primarily involved in the fine-tuning of movements. This suggests that looking at levels of dopamine and its receptors in the striatum may not be useful markers in diagnosing ADHD as they are similar in people with and without ADHD. However, the study did find that people with ADHD have reduced grey matter in several brain networks compared to healthy volunteers.
Interestingly, the study indicated that Ritalin may improve attention if people have poor concentration, regardless of whether people have a diagnosis of ADHD or not. When all of the data from the computerized attention tasks were pooled together, it was found that Ritalin improved attention for low performers from both the ADHD and control groups.
Professor Barbara Sahakian, who supervised the study, said, “We feel these results are extremely important since they show that people who have poor concentration improve with methylphenidate (Ritalin) treatment whether they have a diagnosis of adult ADHD or not. These novel findings demonstrate that poor performers, including healthy volunteers, were helped by the treatment and this was related to increases in dopamine in the brain in an area of the striatum called the caudate nucleus.”
The research suggests that although Ritalin does help with some of the symptoms of ADHD such as poor attention, it does not do this by working directly on the causes of ADHD. This study has important implications for Professor Sahakian’s related work on cognitive enhancing drugs. These drugs such as Ritalin, Modafinil and Adderall which have also been called “smart drugs,” have received significantattention in the media recently.
This research was funded by the Medical Research Council. This news post was adapted from the Medical Research Council’s press release.