Brain Scans Reveal a Surprising Dopamine Difference in Autism

By analysing three different types of brain scan in the same study, researchers have identified new biological differences linked to autism, pointing to the brain's dopamine system as a potentially important part of autism biology.

Researchers from the University of Southern Denmark and Odense University Hospital studied 60 adults using three forms of brain imaging, combining them for the first time to examine the dopamine system, the brain's energy use, and communication between brain regions within a single study. Autistic participants had more dopamine D2 receptors — proteins on brain cells that respond to the neurotransmitter dopamine — than neurotypical participants, suggesting the dopamine system may be an important part of autism biology.

"Our study is the first to investigate the neurotransmitter dopamine, the brain's energy use (glucose metabolism) and communication between brain regions in the same study. This gives us a more nuanced understanding of the neurobiological mechanisms associated with autism," said Laust Vind Knudsen, postdoc at the Research Unit for Psychiatry, Odense University Hospital and the University of Southern Denmark, and the study's first author. Certain deep brain regions in autistic participants showed both greater energy use and more dopamine receptors than the same regions in neurotypical participants, and a greater number of dopamine receptors was associated with higher energy use in the same brain areas.

The researchers also found that the relationship between the dopamine system and communication among brain regions differed between autistic and neurotypical participants. "Our findings suggest that the dopamine system not only differs between autistic and neurotypical people. They also indicate that the dopamine system affects communication between brain regions differently in the two groups. This suggests that the dopamine system may play a more fundamental role in autism than previously thought," Knudsen said.

The researchers stress that the findings do not explain why autism develops and cannot be used to diagnose it; instead, they provide new information about biological variation linked to autism. Because many autistic people are also diagnosed with attention-deficit/hyperactivity disorder, or ADHD, and dopamine plays an important role in that condition too, the results raise questions about whether some dopamine-related mechanisms are shared between the two. The study, involving 60 adults, is the first positron emission tomography, or PET, brain-scan study specifically designed to also examine possible differences between autistic men and women, and the researchers say larger studies are still needed to confirm the results.