Neuroscience researchers find no differences in brain connectivity between children with diagnoses of autism, ADHD, and those with no diagnoses.

In a new study, researchers analyzed fMRI brain imaging data for children with autism diagnoses, ADHD diagnoses, and no diagnoses (referred to as “typically developing”). They specifically looked at functional connectivity, a measure of how well parts of the brain “communicate” with each other. They found that there were no brain differences between any of the diagnostic categories.

The researchers also theorized that executive functioning (a measure of cognitive skills such as attention, memory, planning, and problem solving) might be related to functional connectivity, independent of any diagnosis. However, they found no brain differences between children with different levels of executive functioning, either.

The research, published in NeuroImage: Clinical, was led by Dina R. Dajani at the University of Miami. Other researchers involved hailed from Johns Hopkins University, the Kennedy Krieger Institute, the University of Minnesota, and Yale University. Dajani and the other researchers write:

“This work contributes to a growing literature suggesting that traditional diagnostic categories do not define neurobiologically separable groups.”

Previous research on functional connectivity in the brain has been inconclusive. Some studies have found slight average differences in this biological measure between children with an ADHD diagnosis compared to children without a diagnosis, or children with autism compared to children without a diagnosis.

However, most research has found no such brain differences. Even the differences that have been found could be the result of false-positives, which have plagued the neurobiology field in recent years. According to the researchers:

“The neuroscience field is becoming increasingly aware of the lack of reproducible findings across studies, which may be the result of low sample sizes, inflated false-positive rates due to analytic choices, and heterogeneity inherent to groups of interest.”

Dajani and the other researchers wanted to clarify these contradictory findings, so their study used larger samples and targeted methodology. They studied the fMRI data from 168 children (ages 8-13) divided into three groups: children with an ADHD diagnosis, children with an autism diagnosis and children with no diagnosis (referred to in the paper as “typically developing”). Some children had both autism and ADHD, so additional analyses were performed to assess whether having both diagnoses made a difference.

The researchers found no brain differences between the diagnostic groups. That is, children with “typical development” did not have different brain activity than children with ADHD or autism diagnoses.

The researchers then divided the children up separately by executive functioning—independently of their diagnosis. They made three groups: above average, average, and below average executive functioning. They then compared the functional connectivity for these three groups.

Again, the researchers found no brain differences between the groups. Even the above average and below average executive functioning groups had similar brain activity.

The researchers argue that previous findings of brain differences likely “represent false positives due to low sample size.” They suggest that the diagnostic classification system—at least for these two diagnoses—does not have a basis in neurobiology, nor does the behavioral classification of executive functioning skills.

Their conclusion is that brain science cannot distinguish between ADHD, autism, and typically developing children, nor can it distinguish between different levels of executive functioning.

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Dajani, D. R., Burrows, C. A., Odriozola, P., Baez, A., Nebel, M. B., Mostofsky, S. H., & Uddin, L. Q. (2019). Investigating functional brain network integrity using a traditional and novel categorical scheme for neurodevelopmental disorders. NeuroImage: Clinical, 21(101678). https://doi.org/10.1016/j.nicl.2019.101678 (Link)