In other results, an interesting pattern began to evolve
Both ASD groups, for example, had much wider boundary separations, which meant they were waiting to be sure before they responded than the ADHD or typically developing groups. In contrast, the two ADHD groups had much faster non-decision times, whereas the two non-ADHD groups had similar nondecisions times.
Unlike the previous analysis, which saw a symptom severity pattern develop, “we’re getting two parameters that seem to track much more specifically to specific symptom domains,” observed Dr. Karalunas.
The results suggest there’s a substantial overlap in cognitive impairments in ADHD/ASD. “But we have pretty strong evidence at this point that these similarities are not accounted for by symptom overlap, especially for things like response and inhibition, working memory and processing speed. These seem to be independently related to ADHD and autism, regardless of the level of comorbid ADHD symptoms in the autism group,” said Dr. Karalunas.
The hope is to expand on these types of analyses to address the interaction of cognition-emotion and social cognition, and empirically define groups based on cognitive performance, she said.
Neurocognitive studies
Researchers have also been studying neural networks to assess ASD and ADHD. Roselyne Chauvin, PhD, a postdoctoral associate at Washington University, St. Louis, discussed the concept of “a task generic connectome,” in which researchers look for a common network between targeted task paradigms to get closer to a common alteration across impairments.
In her research, Dr. Chauvin and colleagues looked at connectivity modulations across three tasks: working memory, reward processing tasks, and stop signal tasks, comparing ADHD patients to siblings and controls. The ADHD group showed reduced sensitivity or a smaller number of connections modulated in the tasks compared with the other groups. Researchers wondered where those missed connections were located.
Dividing the cohorts into task generic and task specific groups, Dr. Chauvin and colleagues found that the ADHD group lacked common processing skills. They were also able to identify reproducible missing circuits in the ADHD participants. Among the cohorts, there was a higher modulation of task-specific edges in the ADHD group.
The ADHD patients seemed to be using more task-tailored alternative strategies that were more challenging and suboptimal.
She also previewed her ongoing work with the EU-AIMS Longitudinal European Autism Project (LEAP) database to study ASD-ADHD comorbidity. In this project, she and her colleagues looked at several tasks: probing emotion processing, inhibitory control, theory of mind, and reward anticipation. Comparing ASD groups with or without ADHD comorbidity or a shared connection, she and her team were able to devise a functional profile predictive of ADHD severity. As an example, “for the connection only used by the ASD with ADHD comorbidity, the more they were using those connections of higher amplitude in the modulation, inside this subset of connection, the higher they would have ADHD severity,” said Dr. Chauvin.
Dr. Charlotte Tye
Neural correlates of different behavioral and cognitive profiles haven’t been widely studied, according to Charlotte Tye, PhD, who’s based at the Institute of Psychiatry, Psychology & Neuroscience, King’s College, London. Electroencephalography is a useful technique for understanding the neural correlates of cognitive impairments and teasing apart different models of co-occurrence in ASD and ADHD.
Dr. Tye and colleagues tested this approach in a cohort of boys aged 8-13 years diagnosed with ASD and/or ADHD, measuring EEG while the children did various continuous performance tasks to assess changes in brain activity. Examining P3 amplitude (event-related potential components) they found that children with ADHD or ADHD+ASD showed an attenuated amplitude of the P3, compared with typically developing children and those with ASD.
“This suggests children with an ADHD diagnosis exhibited reduced inhibitory control,” said Dr. Tye. In contrast, children with ASD showed reduced conflict monitoring as indexed by altered N2 amplitude across task conditions.
These, and other studies conducted by Dr. Tye and colleagues indicate that children with ADHD show reduced neural responses during attentional processing, whereas autistic children show typical neural responses, supporting specific profiles.
“Autistic children with a diagnosis of ADHD appear to show the unique patterns of neural responses of autism and ADHD, supporting an additive co-occurrence rather than a distinct condition. This contributes to identification of transdiagnostic subgroups within neurodevelopmental conditions for targeting of personalized intervention, and suggests that children with co-occurring autism and ADHD require support for both conditions,” said Dr. Tye.
An important takeaway from all of these findings is “we can’t look just at how someone does overall on a single test,” said Dr. Karalunas in an interview. “There is a tremendous amount of variability between people who have the same diagnosis, and our research really needs to account for this.”