The lead author, Martine Hoogman of Radboud University Medical Centre in the Netherlands, says the data "confirm that people with ADHD have differences in their brain structure and therefore suggest that ADHD is a disorder of the brain". Nevertheless, the most prominent differences in brain volume were revealed in children.
Hoogman and colleagues analyzed MRI scans for more than 3,200 people in nine countries aged four to 63, of whom 1,713 who had ADHD. Researchers knew that this brain area is involved in recognizing emotional stimuli and regulating emotions. "This is another big confirmation that it is a disorder of the brain and it will help with the stigma that ADHD is something created socially".
While previous studies have also documented some brain differences in those affected, this represents the largest population of people studied.
Kids with attention deficit hyperactivity disorder (ADHD) are often believed to simply be hard, and parents often feel they have failed their child in some way.
The team said that the past reviews which related to changes in brain volume with ADHD had been too small to be conclusive. They also said that people with this condition might have delayed development.
Of seven subcortical brain regions targeted in the study, five, including the amygdala, were found to be smaller in those with ADHD compared with a control group.
The researchers concluded that a delay in brain development is typical of the condition, hoping the analysis would stop people associating it with "difficult children" or bad parenting.
The regions which had a reduced volume were the amygdala, the hippocampus, the nucleus accumbens, the putamen and the caudate nucleus. These drugs have been known to be behind weight gain or loss, suicidal thoughts, and liver damage. The other regions with decreased volume were the caudate nucleus (which plays a role in goal-directed action), the putamen (linked to learning and responding to stimuli), the nucleus acumbens (rewards and motivation), and the hippocampus (which helps form memories).
Typically, people with ADHD have poor attention skills and could be hyperactive.
Given the differences in brain structure they discovered, Hoogman and colleagues suggest that ADHD should be treated like a brain disorder, and not just some label for poor parenting or hard children.
Notably, no differences were found in the brain size of people who took ADHD drugs and those who did not.
Children with ADHD can have trouble adapting to new situations or new rules.
Commenting on the study from an independent perspective, Jonathan Posner of Columbia University, who works in the field of ADHD science, described these findings as an "important contribution".
Another recent study in ADHD dates back to May past year, and posits that children with the disorder have some symptoms also found with rare forms of cancer.