When compared to people who don’t have ADHD, the brains in those who do have a slightly smaller volume overall and specifically in five different regions of the brain according to a study published in The Lancet Psychiatry.
The researchers found that the largest difference was in the amygdala, the region that regulates emotion.
The scientists gathered data from previous studies to look at more than 3,200 people, 1,713 with ADHD and 1,529 without. The participants ranged in age from 4 to 63 years old. MRIs had been used to measure the overall volume of the brain as well as the volumes in seven different brain regions — the pallidum, thalamus, caudate nucleus, putamen, nucleus accumbens, amygdala and hippocampus.
They found that the overall volume of the brains in those with ADHD were smaller than those without ADHD. They also found that five of the seven regions measured were smaller — the caudate nucleus, putamen, nucleus accumbens, amygdala, and hippocampus. The largest difference was in the amygdala, which regulates emotional processing.
The differences were most noticeable in children with ADHD, but small differences remained in adults with ADHD. The use of stimulant medication for ADHD did not seem to affect the outcome. Differences in brain volume were found in those with ADHD who took medication and those that did not.
Many people with ADHD have a low tolerance level to frustration and may also have depression or anxiety. There has been debate over the cause — were these primary symptoms, a second but separate diagnosis, or might they have developed as a result of living with ADHD? The finding of differences in volume in the amygdala points to the possibility that emotional processing difficulties are part of ADHD.
The results on other regions weren’t so surprising. The caudate and putamen are thought to be involved in motor control, motivation and cognitive control. The nucleus accumbens is associated with reward processing, which is also associated with substance abuse. People with ADHD are at a higher risk of developing substance abuse issues.
What does this say about intelligence?
Researchers did not look at neural connections within the brain. They didn’t measure the intelligence of the participants. This study looked only at the size and volume of the overall brain and specific regions. Therefore, the scientists didn’t draw any conclusions about how this relates to intelligence.
Previous research indicates that overall, people with ADHD have a slightly lower IQ. Steven V. Faraone, Ph.D., of The American Professional Society of ADHD and Related Disorders explains that while it is true that people with all different IQs can have ADHD. Many people with ADHD have very high IQs and many have average IQs. One theory is that people with ADHD are more able to compensate for ADHD symptoms and therefore those with lower IQs are more likely to be diagnosed with ADHD and have difficulty with symptoms. Having ADHD, in itself, does not predict intelligence.
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Eileen Bailey is a freelance health writer. She is the author of What Went Right: Reframe Your Thinking for a Happier Now, Idiot’s Guide to Adult ADHD, Idiot’s Guide to Cognitive Behavioral Therapy, Essential Guide to Overcoming Obsessive Love, and Essential Guide to Asperger’s Syndrome. She can be found on Twitter @eileenmbailey and on Facebook at eileenmbailey.