Brain signal reappears after ADHD symptoms fade

The brains of adults who shed attention-deficit/hyperactivity disorder diagnoses seem to outgrow aspects of the disorder. After a childhood diagnosis of ADHD, adults who no longer experience symptoms lack a characteristic asynchrony of brain activity, scientists report June 10 in Brain.

If confirmed in studies involving more people, the asynchrony might serve as a clear marker of active ADHD. Such a sign would allow clinicians to better detect and monitor the disorder, which is characterized by hyperactivity and difficulties focusing, says cognitive neuroscientist Sandra Bond Chapman of the University of Texas at Dallas.

About 60 percent of children diagnosed with ADHD continue to experience symptoms as adults, while the remaining 40 percent see their symptoms ease, says study coauthor Aaron Mattfeld, a neuroscientist at MIT. “No one’s really looked at the brain differences among those two unique groups.”

Mattfeld and his colleagues studied 35 people about 16 years after they received ADHD diagnoses as children. Thirteen of these adults still had an ADHD diagnosis, while 22 of them no longer met criteria for ADHD. Mattfeld and colleagues measured brain activity with functional MRI scans while the participants were awake but doing nothing in particular.

Earlier studies had turned up a key difference in brain activity in both children and adults with ADHD. Within the brain, a series of interconnected hubs form the default mode network (SN: 7/18/09). Although scientists debate what this coordinated network does, the synchrony of two of its hubs — the posterior cingulate cortex and the medial prefrontal cortex — is known to be weaker in people with ADHD.

In the new study, the same disconnect appeared in the brains of adults who still had ADHD.  But in the adults who no longer experienced symptoms, the synchrony had returned, the team found. “It was neat to see it come back,” Mattfeld says. “They looked like people who had never had ADHD.”

Although the default mode network looked as though it had changed in people who no longer had ADHD symptoms, another brain region appeared to stay the same.

That region, called the dorsolateral prefrontal cortex, behaved differently in the brains of people with a history of ADHD compared with 17 people who had never had an ADHD diagnosis, the researchers found. The region of the brain, which is involved in working memory and attention, usually quiets down when the default mode network is active, but in people who had ADHD as children, it remained active even when symptoms disappeared in adulthood. This abnormal activity might contribute to deficits that are common in people with ADHD but not necessarily central to the disease, says Mattfeld.

Larger studies are needed to say whether doctors can use the change in the default mode network as an ADHD marker, Mattfeld cautions. And at this point, it’s unclear whether this brain network relates to behavior.