It's easy to think we all have attention problems, whether you're glued to your smartphone, can't seem to sit still, or drift off while someone's telling us a boring story. A new study published in The Lancet Psychology, however, has found that the brain of someone with real attention deficit hyperactivity disorder is physically different from a normal brain.
In a massive coordinated effort at universities across several continents, more than six dozen scientists analyzed magnetic resonance imaging (MRI) brain scans of 1,713 patients diagnosed with ADHD and 1,529 patients without the condition. The researchers determined that five brain regions—the accumbens, amygdala, caudate, hippocampus, and putamen—are all slightly smaller in people with ADHD. In children younger than 15 years old, the size differential was even more pronounced than in adults over the age of 21.
Of those regions, only the caudate and putamen had already been shown to be smaller in ADHD patients. Previous studies that peered into the structure of the brain for clues about the causes of ADHD often involved too few patients to be able to detect the miniscule size variations that were shown in the new report. A previous MRI scan study by Hoogman had also found a correlation between a smaller total brain volume and more severe ADHD symptoms.
By revealing unique brain changes associated with ADHD, the study might finally put to bed the notion that kids are hyperactive because of bad parenting, overexposure to social media, or playing too many video games. In fact, because the size differences were bigger in children than in adults, the researchers believe that ADHD might be related to slower maturity in these particular brain regions, which eventually catch up to the rest of the brain.
At the same time, the diminished brain differences in grown-ups might indicate that adult ADHD is a separate animal altogether. "We know that some children with ADHD outgrow ADHD, but that there is also a persistent group who still has the disorder in adulthood," says study author Martine Hoogman, a researcher at Radboud University in the Netherlands. "These could be distinct disorders."
The largest variation in size in the ADHD brain was found in the amygdala, indicating that it may be responsible for problems in regulating emotions seen in many ADHD sufferers. Although people with depression also have a smaller hippocampus (which plays a role in memory), the total of five brain regions is enough to give ADHD a distinct signature that differentiates it from scans of brains with depression, schizophrenia, or bipolar disorder.
That doesn't mean you can sign up for an MRI to determine whether you have true ADHD or you're simply hoarding browser tabs—at least not yet. "It's not possible now," Hoogman says. "It might be someday."
Until then, this line of research can help better understand what causes ADHD and better define the symptoms included in a diagnosis. Hoogman says the next step is to explore brain regions in the cortex and the connections between those regions.