People with ADHD, attention-deficit/hyperactivity disorder, have different brain structures than people without ADHD, according to an global team of researchers that conducted the largest brain imaging study of its kind. The link between ADHD and the hippocampus could perhaps arise from that region's involvement in motivation and emotion, they suggest.
Scientists appear to have conclusive proof that ADHD is a physical condition - and not just erratic behavior in children.
The study, the largest to date of the brains of those with ADHD, was conducted by The Lancet: Psychiatry.
ADHD, which is most common in children but also affects adults, causes severe patterns of inattention, hyperactivity and impulsivity.
The researchers were able to conclude that the brain differences were not related to medication people took, to other psychiatric disorders people with ADHD may also have had, or even to the severity of their symptoms.
The long-term effects of drugs like Adderall and Ritalin on the brains and bodies of young people are still under-studied, the CDC said.
From the MRI scans, the team could assess overall brain volume as well as the size of seven regions of the brain that previous studies have linked to ADHD.
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The five areas affected were the caudate nucleus, putamen, nucleus accumbens, amygdala and hippocampus. Existing ADHD meds are very powerful, and cause a plethora of side effects, ranging from weight loss to depression and feelings of suicide. Some have been identified before and make intuitive sense; they involve parts of the brain responsible for controlling impulse, attention and other cognitive functions. They found that the brains of children with the condition were slightly smaller in five regions, including those that control emotions, voluntary movement and understanding.
Typically, people with ADHD have poor attention skills and could be hyperactive.
"The reliability of ADHD research has not been great, because of [small] sample sizes", said Jonathan Posner, who did not take part in the study but who does pediatric brain imaging research at Columbia University Medical School.
"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", lead author Martine Hoogman, Ph.D., said in a news release.
Hoogman said: "We hope that this will help to reduce stigma that ADHD is "just a label" for hard children, or caused by poor parenting".
For those who live and work in the field, she says the study's findings could assist in erasing some of the stigma and misinformation surrounding the disorder. Additionally, research was expected to decide the impact of medication on the brains of the individuals with ADHD, and how they developed as individual get older.