Conducting the largest imaging study of attention-deficit hyperactivity disorder to date, researchers have identified differences in five brain regions, suggesting that the condition should be treated like a brain disorder. They measured the whole brain volume and also the span of seven areas thought to be connected to the disorder.
For the current study, the researchers worked with 1,713 individuals with ADHD and 1,529 without, with ages ranging from 4 to 63 years old. The large impact seen in the amygdala, which regulates emotions, may change the way ADHD is viewed.
Study authors revealed that they did not observe a difference in people who took drugs for ADHD, which means that the drugs don't have an effect on the brain.
The most noteworthy findings relate to the smaller amygdala and hippocampus in patients with ADHD, as those regions haven't previously been conclusively linked to the disorder.
"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", Dr. Hoogman said.
The study involved scanning the brains of 1,713 participants purportedly with ADHD, and 1,529 participants with no signs of any psychological difficulties.
ADHD causes inattention, hyperactivity and impulsivity, although a given person may not show all those traits.
"Similar differences in brain volume are also seen in other psychiatric disorders, especially major depressive disorder", adds Dr. Hoogman.
Previous studies which associated changes in brain volume with ADHD had been too small to be conclusive, the team said. They found that two regions in the ganglia, the caudate and putamen, tend to be smaller in people with ADHD. They have unveiled that this neurological disorder involves a reduced volume in significant brain areas, mainly the amygdala, being responsible for governing emotions.
The study has found that there are differences in the regions of the brain for people with ADHD.
The first author, geneticist Martine Hoogman of Radboud University in the Netherlands, said the amygdala "is a structure that is not so well known to be implicated in ADHD".
This study, due to its much larger size, can make that link, says Arthur Caye, a psychiatry PhD student at the Hospital de Clínicas de Porto Alegre in Brazil who has published research on ADHD, and who was not involved in the study. "Kids with ADHD often have emotional reactivity and poor frustration tolerance". He has suggested that ADHD could be classified as a brain disorder based on the study.
In a statement, she expresses hope "that this will help to reduce stigma that ADHD is "just a label" for hard 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".