ADHD affects approximately 5 percent of children and teens worldwide and is characterized by hyperactivity, impulsivity, and difficulty focusing and paying attention. Right now, the only way to diagnose ADHD is behaviorally; teachers, parents, and healthcare professionals work together to identify children who have the disorder.
Unlike other health conditions, which can be diagnosed by measuring signals within the body called biomarkers, ADHD and many other mental health conditions are diagnosed based on observed symptoms.
“Similar to other psychiatric diseases, ADHD’s diagnosis is made based on the empirical assessment of a psychiatrist,” said Qiyong Gong, director and professor of radiology at the Sichuan University Hospital in China and principal investigator for the study, in an interview with Healthline. “There is no effective diagnosis and treatment mainly due to our poor understanding of the underlying pathophysiology and particularly the lack of objective biomarkers for diagnosis and prognosis.”
A Snapshot of the Brain at Rest
Gong’s study examined 33 boys with ADHD, ages 6 to 16, and compared them with 32 age-matched children without ADHD. First, the subjects completed two behavioral tasks—a card-sorting task and the Stroop test—to measure their ability to pay attention, shift between tasks, and control their focus. Then the researchers scanned each child's brain using resting-state functional magnetic resonance imaging (rfMRI). During regular fMRI, subjects perform tasks while in the scanner to measure how the task affects their brain, but rfMRI measures subjects while they’re doing nothing.
“During the rfMRI scanning, subjects were instructed to relax with their eyes closed without falling asleep and without directed, systematic thought,” explained Gong.
Why measure the brain this way? In the past, researchers had performed fMRI on children with ADHD, but they got mixed and conflicting results, possibly due to the ADHD itself interfering with the subjects as they performed their tasks. On the other hand, rfMRI, measures the background levels of spontaneous nervous-system activity that arise on their own. Gong hoped that rfMRI would paint a clearer picture of what was happening in the children's minds.
It’s All About the Wiring
Those previous studies suggested involvement of the frontostriatal tract, a bundle of connections that link the executive control areas of the brain to the regions governing attention and movement. Gong’s research confirmed that this tract was altered in kids with ADHD, as were a number of others, including the frontoparietal tract (which connects executive control areas to other functions important for attention) and the frontocerebellar network (which connects areas of executive control and movement).
The team also found that levels of baseline activity were altered in a number of brain regions, including the globus pallidus (which controls voluntary movement), the orbitofrontal cortex (which blocks socially inappropriate behaviors), and the superior frontal gyrus (which is in charge of executive control).
These findings show that ADHD is not simply caused by a problem in a single brain region, but that there are widespread differences in wiring throughout much of the ADHD brain.
Gong cautions that this still isn’t the whole picture. “For ADHD, the genetics and the environmental risk factors are all involved,” he said. “Our finding of the alteration of the resting functional network in ADHD tells only part of the story.”
The Future of ADHD Diagnosis
The next step for Gong is to perform larger-scale studies using other imaging techniques to gain a better understanding of these brain changes. Gong warns that the road to a good diagnostic tool for ADHD will be bumpy and complex.
“It’s difficult to predict when the fMRI can eventually become a clinical diagnostic tool,” he said. “The main obstacle is due to the fact that the central nervous system of human beings is complex, let alone that of patients with psychiatric disorders. The psychiatric patients with the same type of disorder could present different clinical symptoms.”
Still, he’s hopeful that his research will one day pave the way to a biomarker-based diagnosis. He says, “It is increasingly evident that the neuroimaging findings are of translational value for ADHD. These so-called psychiatric imaging results not only help us to understand the pathogenesis of the ADHD, but also show great potential to provide the objective biomarker for clinical diagnosis and evaluation. Ultimately, the psychiatric imaging may play an important role in guiding therapeutic intervention in the long run.”