The brains of sufferers of attention deficit hyperactivity disorder (ADHD) are slightly smaller than those not suffering from the condition, according to a study.
The study, which was published in the journal The Lancet Psychiatry and stands as the biggest review of the brains of people with ADHD to date, suggested that the disorder is due to “structural differences” in the brain and is not simply an excuse for antisocial behavior.
“We hope that this will help reduce stigma that ADHD is ‘just a label’ for difficult children or caused by poor parenting,” said the study’s leader author, Martine Hoogman of Radboud University Medical Center in the Netherlands, in a statement reported by AFP.
ADHD is thought to be a developmental disorder that shows signs in childhood and can remain throughout a person’s life. Symptoms include a short attention span, difficulty in time management and organization and being unable to sit still. Around 1.5 percent of children and young people in the U.K. suffer from severe ADHD, according to the charity Young Minds.
The study involved 1,713 people with ADHD and 1,529 without the condition, aged from 4 to 63 years old. Researchers measured overall brain volume, but also the size of seven specific brain regions believed to be associated with the disorder.
The brains of ADHD sufferers had a slightly smaller overall volume, and five of the seven regions—including the amygdala, which is involved in emotional responses—were smaller in people with the condition, the researchers found. The differences were more prominent in children but continued into adulthood.
Hoogman said that similar differences in brain volume were common to other psychiatric disorders, such as major depressive disorder.
The causes of ADHD remain disputed. A 2016 study of 400,000 children between 4 and 17 years old in Taiwan suggested that ADHD was being overdiagnosed, and that in many cases, the differences between children with ADHD and those without could be explained by age: the youngest in a school year group were less mature, and therefore more likely to be characterized as having ADHD, than the oldest in the group.
Drugs, such as Ritalin, are used to treat ADHD and have been linked to adverse side effects, including fluctuations in weight and suicidal thoughts. The present study found no difference between people who had taken ADHD medication and those who had not, suggesting the differences in brain size were not due to the drugs.