As many as five brain regions may not be fully developed in children with attention-deficit/hyperactivity disorder (ADHD), according to a new imaging study.
The differences observed in their study were most prominent in children, but also present in adults with the condition.
The regions affected included the amygdala, which is involved in the regulation of emotion.
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. According to them, their findings may aid in improving the understanding of ADHD, challenging beliefs about the condition to do away with labels attached to it.
"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", she said.
Posner wasn't involved in the study, though he did publish a commentary in the same edition of Lancet Psychiatry based on the research.
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, the researchers said.
Previous studies which associated changes in brain volume with ADHD had been too small to be conclusive, the team said.
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The regions which had a reduced volume were the amygdala, the hippocampus, the nucleus accumbens, the putamen and the caudate nucleus.
The researchers speculate that the amygdala is linked to ADHD through the part it plays in controlling emotion, and the nucleus accumbens through the role it plays in reward processing.
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".
Despite the large numbers of participants of all ages, the study was not created to investigate how ADHD might develop over a person's lifetime.
Jonathan Posner, an associate professor of psychiatry at Columbia University Medical Center in NY, also said the research should help families with children diagnosed with ADHD.
They found no difference between people who were taking or had taken ADHD drugs, and those who had never taken such medications - suggesting that the brain changes were not caused by psychostimulants.
Diagnoses of ADHD have become increasingly common - at least one in 20 children in Canada are estimated to have the disorder.
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". A new study reveals information that suggests that ADHD might be a brain disorder.