The main cause of Attention Deficit/Hyperactivity Disorder (ADHD) is a problem with grey matter in the brain structure and not a brain chemical, according to a study published in Brain on October 29. Dopamine, a chemical in the brain, was previously thought to cause ADHD. In this study, researchers gave methylphenidate (Ritalin) to people with and without ADHD and observed similar levels of dopamine among both groups, report researchers from the University of Cambridge, England.
"These findings question the previously accepted view that major abnormalities in dopamine function are the main cause of ADHD in adult patients. While the results show that Ritalin has a 'therapeutic' effect to improve performance, it does not appear to be related to fundamental underlying impairments in the dopamine system in ADHD," said Trevor Robbins, a co-author of the study.
Researchers conducted a double blind study in which methylphenidate was given to two groups of people. One group included 16 people with a diagnosis of ADHD and the other group consisted of 16 people who did not have the disorder. A portion of the participants in each group was given a placebo.
Two imaging techniques, functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), were combined to measure the effect of methylphenidate on dopamine in each person. The researchers found that the effect on dopamine levels was the same whether or not the person had ADHD. They also observed similar improvements in attention and concentration in the participants who had taken methylphenidate even if they did not have ADHD.
Researchers hope these results will improve clinicians' understanding of the cause of ADHD and help develop effective treatments for this disorder.
ADHD is a disorder that usually begins in childhood. According to WebMD, the symptoms of ADHD can vary but include:
- difficulty sitting still
Many children with ADHD have another disorder such as autism, anxiety or depression. There isn't a cure for ADHD. Common treatments include medications and behavioral therapies.
Dopamine is a chemical in the brain that acts as a neurotransmitter. Neurotransmitters carry signals between neurons or brain cells. Dopamine is important for “concentration or sustained attention, working memory and motivational processes in the brain.”
More information on ADHD is available from the National Institutes for Health.
The study, "A positron emission tomography study of nigro-striatal dopaminergic mechanisms underlying attention: implications for ADHD and its treatment," is published in the journal Brain.