Large Imaging Study Shows Structural Brain Differences in People with ADHD
Critical areas of the brain are smaller in people with ADHD, researchers say, proving that the oft-marginalized condition should be regarded as a brain-based disorder.
February 23, 2017
MRIs of more than 3,000 people provide further evidence that people with ADHD have structurally different brains than people without the condition, according to a new report funded by the National Institute of Health. The differences — which were more pronounced in children than in adults — make it clearer than ever that ADHD is a developmental brain disorder and not simply a “label,” the report’s authors say.
The study, published February 15 in The Lancet, was funded by NIH but conducted by ENIGMA Consortium, an international cooperative focusing on the genetic roots of psychiatric disorders. ENIGMA recruited 3,242 volunteers between the ages of 4 and 63 — 1,713 with ADHD and 1,529 without — to undergo MRI scans.
Participants with ADHD showed smaller volumes in seven key regions of the brain: the caudate nucleus, putamen, nucleus accumbens, pallidum, thalamus, amygdala, and the hippocampus. Of these, most had been associated with ADHD in the past, but the amygdala may be particularly important, researchers note, as it plays a key role in memory, decision-making, and emotional regulation. The hippocampus is similarly involved in both short-term and long-term memory, areas which are often impaired in people with ADHD. Similar size differences have been found in the brains of people with major depressive disorder — a condition that is often comorbid with ADHD.
The variations were largest in children, the researchers said, and though many of the ADHD group were taking medication to treat their ADHD, it didn’t appear to have any effect on the MRI results. The disparity between children and adults led the researchers to hypothesize that ADHD is linked to a delay in brain maturation — though further longitudinal work is needed to fully understand how ADHD brains change throughout the life cycle.
Overall, while these differences are small, the researchers said — in some cases, just a few percentage points — the large sample size allowed them to identify clear patterns, confirming previous studies that had reached the same conclusions but whose small sample sizes rendered them inconclusive. With more than 3,000 participants, this was the largest study of its kind — adding clear evidence that ADHD is a brain-based disorder, and not the result of “bad parenting” or a lack of willpower.
“The results from our study confirm that people with ADHD have differences in their brain structure and therefore suggest that ADHD is a disorder of the brain,” said Martine Hoogman, Ph.D., the lead investigator of the study. “We hope that this will help to reduce stigma that ADHD is ‘just a label’ for difficult children or caused by poor parenting. This is definitely not the case, and we hope that this work will contribute to a better understanding of the disorder.”