Attention deficit (hyperactive) disorder (ADD/ADHD) is one of the most researched areas in child and adolescent mental health. However, much about ADHD — including the precise cause of the disorder — is still unknown.

The brain is the most complex human organ. Therefore, it makes sense that understanding the connection between ADHD and both brain structure and function is also complex. We do know that ADHD is a brain-based biological disorder. Several brain regions and structures (pre-frontal cortex, striatum, basal ganglia, and cerebellum) tend to be smaller.

Studies have shown children with ADHD to have smaller brains by about 3-5 percent, and it is important to point out that intelligence is not affected by brain size. Similar studies have also found that certain areas of the brain were smaller in children with more severe ADHD symptoms. These areas, such as the frontal lobes, are involved in:

• impulse control
• inhibition
• motor activity
• concentration

Overall brain size is generally 5% smaller in affected children than children without ADHD. While this average difference is observed consistently, it is too small to be useful in making the diagnosis of ADHD in a particular individual.

Those with ADHD have impaired executive functioning. Executive functioning is the part of your brain that sorts through all incoming information. It decides what’s important and files away what’s not so that you can focus on the task at hand, whether that’s engaging in conversation, paying the bills, or reading an article on the internet.

In the ADHD brain, executive functioning either doesn’t function at all or functions only to a limited extent. Instead of being able to decide what demands attention immediately and what can wait, the hyperactive brain greets all incoming information as important and needing attention right away.

Studies show that people with ADHD have brains that are physically wired differently than those without it. The brain of those with ADHD develops slower. The hyperactive brain does not build key connections at the same rate as neurotypical brains. When these neural pathways don’t mature and connect, the brain is more easily distracted and has trouble focusing.

Read more for additional ADHD Resources