Attention deficit hyperactivity disorder (ADHD) and autism are both neurodevelopmental disorders that emerge early in life and persist. Up to half of children with an autism spectrum disorder also show marked symptoms of ADHD, and there is considerable genetic and neurobiological overlap between the two diagnoses.
Joel Nigg and his colleagues at Oregon Health and Science University studied these overlaps in detail. Their study involved 159 children aged 7 to 15 years. They found that children with ADHD and those with an autism spectrum disorder have similar deficits, but the presence of ADHD symptoms in the autism group correlates with some key executive function deficits and accounts for some of the apparent similarity between the disorders on task performance. These deficits include impairments in visuospatial working memory and reaction time.
In addition, Nigg’s group used functional magnetic resonance imaging to assess whole-brain network organization and make head-to-head comparisons of ADHD and autism. Despite the similarities in cognitive functioning, they found the nature of the brain network organization in autism and ADHD to be dramatically different.
Brain regions that typically have many links to other parts of the brain (key hubs of brain communication) show low levels of connectivity in children with ADHD, both structurally and functionally. In children with autism, these regions show an overly connected pattern. Nigg’s findings indicate that unique developmental mechanisms may lead to overlapping cognitive deficits in the two disorders.