Autism and ADHD have distinct brain connectivity signatures, study finds

Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) are among the most well-known neurodevelopmental conditions, estimated to affect approximately 1–3% and 5–7% of the global population, respectively. While people diagnosed with ASD can experience difficulties with social communication, repetitive behaviors and a heightened sensitivity to sensory stimuli (e.g., lights, sounds, etc.), those diagnosed with ADHD are often prone to hyperactivity, impulsivity and inattention, which makes it harder for them to focus on tasks for extended periods of time.

ADHD and autism often co-occur, with statistics estimating that 50–70% of individuals with ASD also present symptoms of ADHD. While several past neuroscience studies investigated these two distinct neurodevelopmental conditions, the similarities and differences between their neurobiological underpinnings remain poorly understood.

Researchers at the National Institutes of Health and King’s College London recently carried out a large-scale statistical analysis aimed at comparing the patterns of communication between different regions in the brains of individuals diagnosed with ASD with those observed in the brains of individuals with ADHD. Their findings, published in Nature Mental Health, suggest that although ASD and ADHD can appear together, they are associated with different brain connectivity patterns.

“Autism spectrum disorder (autism) and attention-deficit/hyperactivity disorder (ADHD) often co-occur, although it remains unclear whether these conditions share common neurobiological foundations or exhibit distinct alterations in resting-state brain connectivity,” wrote Luke J. Norman, Gustavo Sudre and their colleagues in their paper.

“We conducted a cross-sectional mega-analytic comparison of functional connectivity patterns linked to autism and ADHD traits in children and adolescents (ages 6–19 years; n = 10,168), with follow-up analyses considering autism (n = 764 autistic; n = 893 neurotypical) and ADHD (n = 2,026 ADHD; n = 2,409 neurotypical) diagnoses.”

As part of their study, the researchers analyzed large amounts of clinical and brain imaging data collected as part of previous studies. This data was collected from over 12,732 children and adolescents diagnosed with either one or both developmental disorders.

The researchers looked at differences and similarities in various regions of the brains of individuals with ASD and ADHD, including the thalamus (a central relay station for sensory and motor signals) and the putamen (known to contribute to movement and learning), as well as various other networks of regions coordinating attention, emotions and self-awareness. Interestingly, they found that ASD was associated with weaker connections between some of these regions and neural networks, while ADHD was linked to stronger connections between the same regions and networks.

“Autism traits and diagnosis were associated with reduced connectivity between the thalamus, putamen, salience/ventral attention and frontoparietal networks, whereas ADHD traits showed the opposite pattern,” wrote Norman, Sudre and their colleagues.

“Hyperconnectivity between the default mode and dorsal attention networks was observed in both autistic and ADHD groups relative to neurotypical individuals and associated with ADHD traits. Despite frequent co-occurrence, autism and ADHD traits exhibit distinct neural signatures, with small effect sizes indicating subtle associations.”

Overall, the results of the large-scale analysis carried out by this research team suggest that although people with ASD can often also exhibit symptoms of ADHD, the two neurodevelopmental conditions have different neural signatures. This key observation could inform future studies focusing on the co-occurrence of the two neurodevelopmental disorders, while also potentially guiding the development of diagnostic tools and therapeutic strategies that account for their different underlying functional connectivity patterns.

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