The brain of the children suffering from Attention-Deficit Hyperactivity Disorder (ADHD) seems to have development delays of up to three years compared with the normal children according to a new study in the U.S.

The new findings appeared in Monday’s edition of Proceedings of The National Academy of Sciences and were made by researchers from the National Institute of Mental Health and Canada’s McGill University.

The study was based on the scanning of 40,000 different sites of the brain cortex in 446 children, teens and young adults half of whom being diagnosed with ADHD. The researchers discovered an average delay of three years in the development of a region in the front called the prefrontal cortex, which is the key for attention, planning and thought.

Almost 2 million U.S. children were diagnosed with ADHD, a disease becomes obvious in preschool and early school years. Children with this disease have a hard time in controlling their behavior and paying attention.

A study published in September revealed that not even a half of the US children who have ADHD receive treatment.

The main concern of the researchers was to find out whether the brain has a different development in children with ADHD or is just a delay. "This is very much in favor of a delay," said Dr. Philip Shaw of the National Institute of Mental Health (NIMH), lead author of the study.

The researchers also wanted to check on when and where the cortex reached peak “thickness,” which marks the maturity of the brain.

They discovered that cortex reached peak thickness at the age of 10.5 in children with ADHD, compared with the age of 7.5 in normal children.

"We know ADHD is a real problem for children and their families and the schools, and it does need treatment," Dr. Shaw said.

In spite of the delayed development in children with ADHD, there are signs that the brain still follows a normal pattern of development.

"In children with ADHD, the brain matures in a normal pattern but is delayed by three years in some regions, when compared to children without the disorder," said Dr, Shaw.

"This is a breakthrough study. It confirms what pediatricians have been saying for years. It is clear now that there is a delay in brain development," said Dr. James McGough, professor of clinical psychiatry and director of the ADHD program at the University of California at Los Angeles.

The researchers said that the new study might be the starting point for new treatments for this psychiatric disease.