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Attention deficit hyperactivity disorder (ADHD) symptoms include difficulty paying attention or lack of focus, impulsivity, irritability and forgetfulness. This is why there is a general notion that it is a motivational issue and character deficit that resulted from bad parenting.

Martine Hoogman, PhD, a geneticist from Radboud University Medical Center in the Netherlands however said that this is not the case. Dr. Hoogman is the chief investigator of the study that was published online last February 15 in the journal The Lancet Psychiatry.

Dr. Hoogman also told The Huffington Post that like other psychiatric disorders, there are neurobiological substrates or changes in the brains with of persons with ADHD. The researchers hope these findings will help shed light into the matter and reduce the stigma often associated to children and adults with the disorder.

In 2013, the researchers formed the Enigma ADHD Working Group to gather data MRI from both the healthy control group and those diagnosed with ADHD across 23 sites.

The participants are from ages 4 to 62 years old and with 1,713 individuals with ADHD and 1,529 from the unaffected group.This meant examining and assessing differences between subcortical structures and intracranial volumes from MRI scans of over 3,000 subjects.

The researchers looked at the different regions of the brains based on the MRI data and this revealed that 5 regions of the brains of those with ADHD are smaller. Dr. Hoogman also said that they have similar 'effect sizes' as the brains of those with depression or obsessive-compulsive disorder (OCD).

The affected regions are the amygdala, associated with processing emotions like fear and pressure, the hippocampus which affects emotions, memory and learning, and the striatum area, including the caudate nucleus, putamen and nucleus accumbens which helps control motivation, pleasure and the brain's reward system.

The study also revealed that the differences are more prominent in children compared to adults suggesting that ADHD involves delay in brain development though as people with the disorder develop, they eventually 'catch up'. Researchers further agree that psychostimulants did not affect the brain volumes of participants.

Dr. Hoogman said that their project only looked at a small part of the brain and that there is still a long way to go.