fMRI scans on ADHD patients suggest that rather than being a single condition, Attention Deficit Hyperactivity Disorder includes multiple disorders – with each displaying common symptoms caused by different neurobiological pathways, affecting unique parts of the brain.
For the study, 117 adolescents who had previously been diagnosed with ADHD were assessed on their impulsive behavior, a common symptom of ADHD. The researchers identified three different groups of patients in the study.
One group showed a preference for immediate reward, a second group had impulsive motor responses during fast-moving visual tasks, while a third group exhibited near normal performance in both tasks when compared with the non-ADHD diagnosed subjects that were also assessed during the study.
The researchers explained that without these tests, it would not be possible to distinguish the groups clinically, yet it was clear that while they all had a common ADHD diagnosis, there was far more to ADHD than was previously thought.
The study suggests a rethink about the disorder is required, as adolescents diagnosed with the disorder are not all the same, neurobiologically speaking. In fact, the researchers did not identify any common abnormalities between the groups.
Patients were also subjected to functional magnetic resonance imaging tests to determine patterns between the performance in the tests and disfunction in the brain. The fMRI scans showed there was no single core ADHD profile of brain dysfunction between each of the three subgroups, although in each of the three subgroups, there was dysfunction in the same area of the brain, that were common to each specific type of behavioral impairment.
The study suggests that while ADHD is a common diagnosis, patients could well be suffering from one of three different disorders, although to confirm that is the case would require more research.
The study also suggests that patients receiving a diagnosis of ADHD would benefit from undergoing different clinical assessments to identify which type of brain dysfunction that is contributing to their symptoms, and doing so would help to select the best treatment for the form of the disorder they are suffering from. While there are treatments that can help alleviate some of the symptoms of the disorder, they may not be equally effective for all three of the subgroups identified.
“Ultimately, by being open to the idea that psychiatric disorders like ADHD might be caused by more than one factor, it might be possible to advance our understanding of causes and treatments more rapidly,” said first author of the study, Dr. Michael Stevens.
The study – Functional Neuroimaging Evidence for Distinct Neurobiological Pathways in Attention-Deficit/Hyperactivity Disorder – was recently published in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.