A group of researchers who used neuroimaging to study the brain regions in children and adults with attention deficit hyperactivity disorder (ADHD) have found the condition should be considered a brain disorder.

The study, published in The Lancet, evaluated more than 1,700 participants with ADHD and more than 1,500 without. Participants ranged in age between 4 and 63 years old. Each participant had an MRI scan that measured their overall brain volume and the size of seven regions of the brain linked to ADHD. Researchers also noted if the participants had ever taken psychostimulant medication, such as Ritalin.

Data suggested that the caudate nucleus, putamen, nucleus accumbens, amygdala and hippocampus had an overall smaller brain volume in people with ADHD.

"These differences are very small—in the range of a few percent—so the unprecedented size of our study was crucial to help identify these. Similar differences in brain volume are also seen in other psychiatric disorders, especially major depressive disorder,” said lead author Martine Hoogman, PhD, in a statement.

Most of these differences showed up largely in the brains of children with ADHD, compared to the adults with ADHD.

"The results from our study confirm that people with ADHD have differences in their brain structure and therefore suggest that ADHD is a disorder of the brain," said Hoogman. "We hope that this will help to reduce stigma that ADHD is 'just a label' for difficult children or caused by poor parenting. This is definitely not the case, and we hope that this work will contribute to a better understanding of the disorder."