Tests of brainwaves using EEG may be helpful in distinguishing subtypes of ADHD, helping to diagnose whether a teen's symptoms are mainly inattention or mainly hyperactivity and impulsiveness.
The two subtypes of attention-deficit/hyperactivity disorder (ADHD) are known as "inattentive" or "combined" and as well as telling these apart, the brain tests also help to rule out non-ADHD adolescents.
The researchers, publishing their study in the journal Biological Psychiatry, say the electroencephalogram (EEG) readings illustrate "that these groups display distinct physiological profiles."
This means there may be an objective biological test for differences that are subjectively observed in the clinic.
"This study shows that there are changes in brainwaves related to visual processing and motor planning that can be used to distinguish ADHD subtypes," says Ali Mazaheri, assistant professor University of Amsterdam, the Netherlands, and guest researcher at the Center for Mind and Brain of the University of California, Davis.
"ADHD subtypes appear subjectively very different in the clinical setting, but there are few objective physiological markers that have been able to detect those differences."
The study, running from 2009 to 2013, was split between 23 children without ADHD and 17 who had the inattentive- or combined-type disorder. All the participants were between 12 and 17 years of age.
The teens wore EEG caps with 32 electrodes during evaluations of their performance on a computer task. They were given visual cues to help with their performance, with some cues being more helpful than others.
This presented a challenge to someone with ADHD since making the correct response meant overriding an initial impulse.
For example, one computer task asked the child to look at a series of arrows pointing in different directions on the screen, and then indicate the direction in which the center arrow pointed. In the following example the center arrow is pointing to the left: >>>.
After viewing the visual cues, the teens' alpha and beta brainwaves were read on EEG, and differences were seen between the teens with the two ADHD subtypes. The youngsters developing without ADHD could also be distinguished.
The researchers say:
"The alpha wave patterns of teens with the inattentive type of ADHD did not process the important information in the visual cues, limiting their ability to succeed."
Meanwhile, measurements of beta wave patterns helped monitor motor task performance, distinguishing teens who had the greatest difficulty pressing a button - those with the combined-type ADHD.
Improving the sensitivity of ADHD treatments
The results of this study challenge the idea that combined-type ADHD is a more severe form of the disorder than the inattentive type. The researchers say that, rather, it seems to be a different type of ADHD, not simply one that displays additive effects.
One of the co-authors Catherine Fassbender, a research scientist with the MIND Institute at UC Davis, says this may help to inform more sensitive treatments:
"This research also gives us clues regarding the development of treatments to address the underlying processing differences between ADHD subtypes.
Most treatments for ADHD do not take subtype differences into account."
She concludes: "Our findings suggest targets for treatment should differ for the ADHD inattentive versus combined subtypes, and that advanced analysis of brainwaves may provide a biomarker for testing treatment responses."
Growing importance of brainwave tests in ADHD
Medical News Today recently reported another test that also uses EEG to help in the diagnosis of ADHD.
The US Food and Drug Administration approved the NEBA System in July 2013, which, "along with other clinical information, may help healthcare providers more accurately determine if ADHD is the cause of a behavioral problem."
EEG has also been investigated as part of treatment as well as diagnosis for children with ADHD. A recent study found that outcomes were improved by combining EEG feedback with drug treatment.
Knowing that EEG feedback on its own has an effectiveness rate "as high as 60-70%" and "results in long-term steady improvement on emotional, behavioral and academic performance, as well as improved cognition and performance in daily activities" the scientists ran a randomized trial of EEG feedback in combination with the stimulant methylphenidate (brand named Ritalin in the US).
The results of the study, from Peking University and published in Swiss Medical Weekly, meant that some patients were able to reduce the dose of methylphenidate, ameliorating side effects that can otherwise cause poor adherence to therapy. "Stimulants can affect appetite and sleep, and potentially affect development as well," the authors say.
Their study adds the weight of a "strict double-blind, randomised controlled trial" to confirm the "effectiveness" of combining EEG feedback and methylphenidate treatment.