In another study released in November 2017, 117 adolescents with ADHD were assessed for different types of impulsive behavior. Three distinct groups emerged based on their performance: one group demonstrated impulsive motor responses during fast-moving visual tasks (a measure of executive function); another group showed a preference for immediate reward; and a third group performed relatively normally on both tasks as compared with 134 non-ADHD adolescents. The 3 ADHD subgroups were almost indistinguishable in terms of clinical symptoms.
Researchers then used functional magnetic resonance imaging (fMRI) to investigate how these different impulsivity-related test profiles related to brain dysfunction.
Each subgroup had dysfunction in different brain regions, related to their specific type of behavioral impairment, and there was not a single fMRI-measured abnormality that could be found in all three ADHD subgroups.
Stevens MC, Pearlson GD, Calhoun VD, Bessette KL. Functional neuroimaging evidence for distinct neurobiological pathways in attention-deficit/hyperactivity disorder.
Biol Psychiatry, https://doi.org/10.1016/j.bpsc.2017.09.005
While MRIs and fMRIs are not yet available to diagnose ADHD, continuing research is providing more information on the neurobiological basis of ADHD and its various subtypes.
