New brain imaging study reveals dopamine system differences in autistic adults

A team of researchers in Denmark set out to answer a deceptively simple question: what does autism look like inside the brain? The answer, they discovered, required looking at the problem from three angles at once.

Laust Vind Knudsen and his colleagues at the University of Southern Denmark and Odense University Hospital recruited 60 adults—some autistic, some not—and subjected them to an unusual combination of brain scans. They used positron emission tomography to map dopamine receptors, measured glucose metabolism to track energy consumption, and examined how different brain regions communicate with one another. No one had done all three simultaneously before. What emerged was a picture far more intricate than previous research had suggested.

The headline finding was straightforward enough: autistic participants had more dopamine D2 receptors than their neurotypical counterparts, particularly in deeper brain structures. But the story didn't end there. Those same regions also burned more energy. And the way dopamine influenced communication between brain areas worked differently in autistic brains than in typical ones. Knudsen, the study's lead author, emphasized that this wasn't simply a matter of more or less of one thing. The dopamine system appeared to operate on fundamentally different principles.

Why this matters requires understanding what dopamine actually does. It's a chemical messenger that nerve cells use to talk to each other, playing roles in motivation, learning, movement, and reward. The D2 receptor—the specific type the researchers examined—has already been linked to ADHD and other neurological conditions. In fact, the only FDA-approved medications specifically for autism target this same receptor, used to reduce aggression and irritability in autistic children. The fact that autistic brains show structural differences in this system suggests it deserves far more attention than it has received.

Previous autism research had largely focused on how brain regions communicate, with far less attention paid to the chemical messengers that enable that communication. By examining neurotransmitters, energy use, and connectivity together, Knudsen's team identified relationships that had remained invisible before. The study was also the first PET imaging work specifically designed to investigate whether these patterns differed between autistic men and women, though the researchers note that larger studies will be needed to confirm and extend these findings.

The implications ripple outward in unexpected directions. Around 40 percent of autistic people also receive an ADHD diagnosis—a strikingly high overlap that has long puzzled researchers. If both conditions involve dopamine system differences, that overlap might finally have a biological explanation. Knudsen and his team are careful to note what their work does not do: it does not explain why autism develops, and it cannot be used to diagnose the condition. What it does provide is a more textured understanding of the biological mechanisms at play, and new questions worth pursuing.

The researchers emphasize that brain research on autism should serve a particular purpose: not to change autistic people, but to deepen understanding of neurodiversity and create better conditions in society. The findings suggest the dopamine system may play a more fundamental role in autism than previously thought—a discovery that opens new avenues for investigation and, potentially, for understanding why certain conditions so often travel together.