“For the study, a team of Dutch neuroscientists analyzed MRI scans of the brains of more than 3,200 people between the ages of four and 63 years old (with a median age of 14 years old), measuring total brain volume as well as the volume of seven brain regions thought to be linked to ADHD.

Roughly half of the participants had a diagnosis of ADHD.

The brain scans revealed that five brain regions were smaller in people with ADHD. These include the amygdala, an almond-shaped structure involved in processing emotions like fear and pleasure; the hippocampus, which plays a role in learning, memory and emotion; and three brain areas within the striatum ― the caudate nucleus, the putamen and the nucleus accumbens. The structures within the striatum are involved in the brain’s reward system and in its processing of dopamine, a neurotransmitter that helps control motivation and pleasure.

These differences were more dramatic in children than in adults, leading the study’s authors to conclude that ADHD involves delayed brain development. It appears that as the brains of people with ADHD develop and mature, these brain regions “catch up” to the brain regions of people without ADHD.”