A small 2026 brain-imaging study found that autistic young people who also had attention-deficit/hyperactivity disorder (ADHD) showed weaker resting-state connectivity between several brain regions than autistic peers without ADHD.
The researchers interpreted the pattern as evidence that autism with ADHD may represent a distinct variant of autism rather than simply a more severe form. The results describe group-level differences, however, and cannot show that altered connectivity causes symptoms or identify whether an individual has ADHD.
What the study found
The analysis included 69 people divided into three equally sized groups: 23 autistic participants with ADHD, 23 autistic participants without ADHD, and 23 non-autistic comparison participants. The groups were similar in sex, average age, IQ, study site and head movement during scanning. The two autistic groups also had similar autism symptom scores on standard interviews and observation tests.
When the two autistic groups were compared directly, the autism-plus-ADHD group had weaker connectivity in eight brain-region pairs and stronger connectivity in none. The differences included connections involving the left hippocampus, the putamen and thalamus; links between the posterior cingulate cortex, the right insula and the anterior cingulate cortex; and connections involving executive and salience regions with frontal and temporal areas.
The anterior cingulate cortex was the only starting region with differences specific to the autism-plus-ADHD group. Compared with non-autistic participants, this group also showed lower connectivity between the anterior cingulate cortex and a frontal planning region, the thalamus and the posterior cingulate cortex.
Shared patterns and differences
Many of the differences from non-autistic participants appeared in both autistic groups, particularly in memory-related areas, the default mode network and executive regions. The autism-plus-ADHD group had 10 stronger and five weaker connections than the non-autistic group.
A few connections were specific to the autism-only group, including stronger links between the left hippocampus and deep brain structures. No connection showed a stepwise pattern in which the autism-plus-ADHD group was furthest from non-autistic participants and the autism-only group fell in between.
These findings led the researchers to argue against treating autism with ADHD as merely a more intense version of autism. Instead, the connectivity patterns may reflect a different combination of characteristics. That interpretation remains provisional because the study was small and requires replication.
Connectivity and autism-related traits
The researchers also examined whether connectivity was associated with autism-related traits within each autistic group. In the autism-only group, stronger connectivity between the hippocampus and an anterior temporal-lobe region was associated with milder verbal communication problems. The reported correlation was r = −0.62. The corresponding association was not clear in the autism-plus-ADHD group, where r = 0.17.
Another connection, between posterior and anterior cingulate regions, was associated with milder repetitive behaviors in the autism-only group, with r = −0.48. The autism-plus-ADHD group showed an opposite but not statistically significant trend, with r = 0.42.
Each symptom correlation was based on about 21 people, and some results lost significance after correction for multiple tests. These analyses therefore do not establish reliable individual-level markers.
Why the results need caution
The researchers analyzed existing resting-state MRI scans from two sites in the Autism Brain Imaging Data Exchange I dataset: New York University and Kennedy Krieger Institute. Because the study was cross-sectional, it captured connectivity and characteristics at one point rather than following people over time.
Resting-state connectivity measures how activity in different brain areas fluctuates together when a person is not performing a task. Connectivity during memory, attention or other tasks could show different patterns. Although the researchers said support programs for autistic people with ADHD might pay more attention to memory, memory was not tested in this study.
The sample was mostly male, had average IQ, came from two sites in one older dataset, and did not report medication use. There was also no ADHD-only comparison group, so the study cannot separate effects associated with ADHD from effects associated with having both autism and ADHD.
Only two of the reported differences remained at a stricter statistical cutoff. Larger, independent studies, including work using datasets such as ABIDE II, are needed to test whether the findings hold. Brain scans of this kind are research tools, not diagnostic tests for autism or ADHD.
AI tools were used to assist with the preparation of this article under our editorial standards.
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