New Research Challenges Old Theories about ADHD and OCD Brains

A meta-analysis of 90 studies pinpointed specific differences between ADHD and OCD brains that may help doctors design better treatments for each condition.
ADHD News Feed | posted by Devon Frye

ADHD and OCD share so many features — impulsive behavior, trouble focusing, and fidgety movements — that researchers have long wondered if the two conditions originate in the same part of the brain. Now, a landmark study has identified marked differences between ADHD and OCD brains, putting old hypotheses to rest and possibly paving the way for new treatment strategies for both conditions.

The study, published June 8 in JAMA Psychiatry, was a meta-analysis of 90 studies — with a combined total of more than 5,000 subjects — that had been published before September 30, 2015. Each study focused on one of the two conditions and used voxel-based morphometry (VBM) and functional MRI (fMRI) scans to assess each patient’s brain.

The combined results showed that patients with ADHD had significantly less gray matter volume in their basal ganglia, a structure at the base of the brain that’s involved in movement and emotions. They also had decreased function in that area of the brain. OCD patients, on the other hand, showed increased levels of both gray matter and function in the basal ganglia.

ADHD patients also showed less function in the ventrolateral prefrontal cortex, while patients with OCD showed lower function in the medial prefrontal cortex.

The conclusions were significantly more different than some researchers had previously hypothesized. But they make a lot of sense, researchers say. Impulsivity and compulsivity are generally considered to be at opposite ends of the “behavioral spectrum,” and these brain differences may help explain why stimulants work for the treatment of ADHD but exacerbate OCD symptoms.

More important, these results lay the groundwork for new treatments for both ADHD and OCD, the researchers say. Patients with OCD who struggle with an under-functioning medial prefrontal cortex, for example, may benefit from neurofeedback therapy that specifically targets this region. For patients with ADHD, these results may give stimulant manufacturers a clearer idea of which areas of the prefrontal cortex they should target.

The logical next step, says lead researcher Katya Rubia, Ph.D., Department of Child and Adolescent Psychiatry, Institute of Psychiatry, Psychology, and Neuroscience, King’s College London, will be to study the crossover group of patients with both ADHD and OCD. The study looked at “pure” ADHD and OCD, but in reality, the two conditions have a 30 percent comorbidity rate — and almost no research has looked at this confounding group.

“It’s interesting that, clinically, [ADHD and OCD] can co-occur,” said Rubia. “You can have a child with obsessive symptoms, who, at the same time, is inattentive and compulsive.

“Given that they have opposite abnormalities [in the brain],” she added, “the question is, what's going on in those who have impulsiveness and compulsiveness?”


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