Summary: A new study clarifies that adolescents diagnosed with attention-deficit/hyperactivity disorder (ADHD) fall into three distinct neurobiological subgroups, each with different brain impairments and no single common abnormality across all groups.
Source: Elsevier.
Researchers report that adolescents diagnosed with attention-deficit/hyperactivity disorder (ADHD) exhibit distinct patterns of brain dysfunction, indicating the disorder may not have a single, unified neurological cause. Instead, the study finds three separate subgroups defined by different behavioral and brain-imaging profiles, with no shared neural abnormality that is common to all groups.
The findings, published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, challenge conventional views of ADHD as a single disorder with modest variations. “This study found clear evidence that adolescents diagnosed with ADHD are not neurobiologically identical,” said Dr. Michael Stevens, first author and researcher at the Olin Neuropsychiatry Research Center, Hartford, CT, and Yale University. The results suggest that what clinicians label as ADHD may instead represent a constellation of distinct conditions that lead to similar outward symptoms through different brain mechanisms.
The research team assessed 251 adolescents aged 12 to 18: 117 diagnosed with combined-subtype ADHD and 134 non-ADHD control participants. They measured two key aspects of impulsive behavior commonly associated with ADHD: behavioral inhibition (motor response inhibition) and preference for immediate reward. Taxometric analyses of the cognitive test results identified three subgroups among the adolescents with ADHD. One subgroup showed marked impulsive motor responses on fast-paced visual tasks, indicating executive function and inhibition deficits. A second subgroup displayed a strong preference for immediate rewards, implicating altered reward processing. The third subgroup performed similarly to the non-ADHD controls on these tasks, showing relatively typical task performance despite meeting clinical criteria for ADHD.
“These three ADHD subgroups were largely indistinguishable on standard clinical evaluation,” Dr. Stevens explained. “Without specialized cognitive testing, a clinician would have had no reliable way to separate patients into these distinct neurobiological groups.” To link behavior with neural function, the team used functional magnetic resonance imaging (fMRI) during tasks designed to probe reward anticipation and motor response inhibition.
fMRI data revealed that each subgroup exhibited dysfunction in brain regions corresponding to their behavioral profile. Participants with motor inhibition deficits showed altered activity in neural circuits that support executive control. Those who preferred immediate rewards displayed abnormalities in brain systems that process reward anticipation and valuation. Crucially, the researchers found no single fMRI-measured abnormality present across all three ADHD subgroups despite their similar clinical presentations.
“Rather than a shared neural signature for ADHD, different neural systems related to executive function and reward processing appear to contribute independently to ADHD symptoms,” said Dr. Cameron Carter, Editor of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging. This supports multiple-pathway models in which similar psychiatric symptoms arise from distinct neurobiological routes.
The investigators emphasize that additional research is needed to confirm and extend these results, but they argue that the findings could reshape research and clinical practice. Dr. Stevens noted that recognizing multiple neurobiological pathways to ADHD could accelerate progress in understanding causes and improving treatments: “If psychiatric conditions like ADHD arise from more than one biological factor, then identifying those factors could make it possible to tailor interventions more effectively.”
Dr. Carter added that clinical assessment strategies that identify the specific type of neural dysfunction underlying a patient’s symptoms may enable more targeted treatment choices. For instance, a medication that appears ineffective across a mixed ADHD population might be beneficial for a particular neurobiological subgroup. Personalizing treatment based on neurocognitive and imaging profiles could improve outcomes and reduce trial-and-error prescribing.
Source: Elsevier
Publisher: Organized by Neuroscience News.
Image Source: Image in the public domain.
Original Research: Abstract for “Functional Neuroimaging Evidence for Distinct Neurobiological Pathways in Attention-Deficit/Hyperactivity Disorder” by Michael C. Stevens, Godfrey D. Pearlson, Vince D. Calhoun, Katie L. Bessette in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging. Published online September 22, 2017; doi:10.1016/j.bpsc.2017.09.005
Elsevier. “Brain Imaging Reveals ADHD as a Collection of Different Disorders.” Neuroscience News. Published November 7, 2017.
Abstract
Functional Neuroimaging Evidence for Distinct Neurobiological Pathways in Attention-Deficit/Hyperactivity Disorder
Background
A major challenge in clinical neuroscience is integrating varied and sometimes conflicting evidence about neuropsychological deficits and brain dysfunction in psychiatric disorders into models that guide research on causes and treatments. Multiple-pathway models propose that similar psychiatric symptoms can arise from dysfunction in different neural systems. This study evaluated predictions from dual-pathway models of ADHD by testing whether deficits in reward processing and executive function map onto distinct, specialized neural systems.
Methods
Behavioral inhibition and preference for immediate rewards were measured in N = 251 adolescents ages 12 to 18, including participants diagnosed with DSM-IV combined-subtype ADHD and non-ADHD control subjects. Taxometric analyses of test performance identified subgroups, which were then compared using fMRI during a monetary incentive delay task (reward anticipation) and a go/no-go task (motor response inhibition).
Results
Three ADHD subgroups emerged consistent with separate pathways: (1) ADHD with executive function and motor inhibition deficits, (2) ADHD with both executive and reward deficits, and (3) ADHD with relatively normal test performance. Each cognitive domain corresponded to distinct patterns of brain dysfunction. Importantly, no brain abnormality was common to all ADHD subgroups, even though the groups showed similar clinical ADHD characteristics.
Conclusions
These results suggest combined-subtype ADHD may represent a collection of discrete disorders in which similar behavioral outcomes arise from different neurobiological pathways. The findings caution against single-deficit models for individual ADHD patients and encourage consideration of biologically defined, multifactorial models for psychiatric diagnoses.
“Functional Neuroimaging Evidence for Distinct Neurobiological Pathways in Attention-Deficit/Hyperactivity Disorder” by Michael C. Stevens, Godfrey D. Pearlson, Vince D. Calhoun, Katie L. Bessette. Biological Psychiatry: Cognitive Neuroscience and Neuroimaging. Published online September 22, 2017; doi:10.1016/j.bpsc.2017.09.005