The differences observed were most prominent in the brains of children with ADHD, but less obvious in adults with the disorder. Similar differences in brain volume are also seen in other psychiatric disorders, especially major depressive disorder." said lead author Dr Martine Hoogman, Radboud University Medical Center, Nijmegen, The Netherlands. "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. The study found that overall brain volume and five of the regional volumes were smaller in people with ADHD - the caudate nucleus, putamen, nucleus accumbens, amygdala and hippocampus. The researchers also noted whether those with ADHD had ever taken psychostimulant medication, for example Ritalin. The new international study measured differences in the brain structure of 1,713 people with a diagnosis of ADHD and 1,529 people without, all aged between four and 63 years old.Īll 3,242 people had an MRI scan to measure their overall brain volume, and the size of seven regions of the brain that were thought to be linked to ADHD - the pallidum, thalamus, caudate nucleus, putamen, nucleus accumbens, amygdala, and hippocampus. Areas thought to be involved in ADHD are located in the basal ganglia - a part of the brain that controls emotion, voluntary movement and cognition - and research has previously found that the caudate and putamen regions within the ganglia are smaller in people with ADHD. Previous studies have linked differences in brain volume with the disorder, but small sample sizes mean results have been inconclusive. The disorder affects more than one in 20 (5.3%) under-18 year olds, and two-thirds of those diagnosed continue to experience symptoms as adults. The authors say the findings could help improve understanding of the disorder, and might be important in challenging beliefs that ADHD is a label for difficult children or the result of poor parenting.ĪDHD symptoms include inattention and/or hyperactivity and acting impulsively. The study is the largest to look at the brain volumes of people with ADHD, involving more than 3,200 people. Attention-deficit hyperactivity disorder (ADHD) is associated with the delayed development of five brain regions and should be considered a brain disorder, according to a study published in The Lancet Psychiatry.