“Size” in relation to ADHD refers to the delayed development of five brain regions. ADHD symptoms include inattention and/or hyperactivity and acting impulsively. A new international study measures differences in the brain structure of 1713 people with a diagnosis of ADHD and 1529 people without, all aged between four and 63 years old. ADHD has been associated in previous studies with the brain’s basal ganglia, in particular, the caudate and putamen regions within the ganglia. Using MRI scans, the researchers find that five regional volumes were slightly smaller in people with ADHD. Overall brain volume also was smaller. The differences observed were most prominent in the brains of children with ADHD, but less obvious in adults with the disorder.
At the time of their MRI scan, 455 people with ADHD were receiving psychostimulant medication and 637 had had the medication in their lifetime. The different volumes of the five brain regions involved in ADHD were present whether or not people had taken medication.
Researchers believe the results for this large sample confirm that ADHD is a disorder of the brain rather than a behavior problem.