Attention deficit hyperactivity disorder (ADHD) is one of the most commonly diagnosed psychiatric disorders among children in the United States. Despite the prevalence of ADHD, there has not been much evidence for a physiological profile of the disorder. However, research by the University of California Davis MIND Institute and the Center for MIND and Brain has uncovered a possible biomarker for two ADHD subtypes, which could lead to treatments that take these discrete subtypes into account.

Researchers evaluated 57 children between aged 12 and 17. There were 23 children without ADHD and 17 with either inattentive-type or combined-type ADHD. Each participant worked through a computer task while wearing an electroencephalogram (EEG) cap. During the task, the teens received visual cues to help them perform better, but some of the clues were tricky and required the teens to reject their initial impulse in order to correctly meet the objective. The researchers then assessed both their performance on the task and their brain wave data gathered from the EEG.

The researchers found differences between the groups in both alpha waves, which mainly originate from the occipital lobe, and beta waves, which are associated with motor tasks. The alpha wave data indicated that the teens with the inattentive-type ADHD did not process critical visual cues effectively, which impacted their performance on the computer task. Meanwhile, a deficiency in beta waves was correlated to poor performance on the motor aspect of the task—pushing a button. The combined-type ADHD participants exhibited the least amount of beta wave activity.

Previous work in ADHD has suggested that combined-type ADHD might be a more severe form of ADHD, but this research suggests that there are distinct problems and, perhaps, distinct causes for both inattentive- and combined-type ADHD.

This study also indicates that there may exist “unique impairments” between subtypes and it may “give us clues regarding the development of treatments to address the underlying processing differences between ADHD subtypes,” according to Catherine Fassbender of the MIND Institute. “Our findings suggest targets for treatment should differ for the ADHD inattentive versus combined subtypes.”

This research is published in the journal Biological Psychiatry.

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