Difficulty in maintaining attention, hyperactivity and impulsiveness in children with attention-deficit hyperactivity disorder (ADHD) may be due to delayed development of five brain regions, proving that it is a brain disorder and not the result of bad parenting, researchers say.

The findings, published in The Lancet Psychiatry, showed that in people with ADHD, the overall brain volume as well as nucleus accumbens, amygdala and hippocampus- brain regions within the basal ganglia that controls emotion, voluntary movement and cognition- remains smaller than those without the disorder.

Previous studies had showed that other brain regions such as caudate and putamen are also smaller in people with ADHD.

Further, these differences were most prominent in the brains of children with ADHD, and less obvious in adults with the disorder, a finding that might be important in challenging beliefs that ADHD is a label for difficult children or the result of poor parenting, the researchers said.

"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," said lead author Martine Hoogman at Radboud University Medical Center in the Netherlands.

"We hope that this will help to reduce stigma that ADHD is 'just a label' for difficult children or caused by poor parenting," Hoogman added.

Similar differences in brain volume are also seen in other psychiatric disorders, especially major depressive disorder, the researchers said.

For the study, the team 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.