Neuroimaging studies have found that autistic people whose cortical thickness deviates most from that of their neurotypical autistic peers tend to experience greater social and communication difficulties. In people with autism, the cortical regions that showed the greatest differences in thickness compared with neurotypical people tended to have higher densities of serotonin receptors. This study provides evidence linking brain structure, neurochemistry, and behavioral characteristics of autism. The paper was published in autism research.
Autism is a neurodevelopmental condition that affects how a person communicates, interacts with others, processes sensory information, and experiences the world. It is called a spectrum because its characteristics and level of support needs vary widely from person to person.
Some people with autism have difficulty interpreting social cues, maintaining conversations, and understanding unspoken social rules. Some people can communicate fluently but find social interactions exhausting, confusing, or overwhelming. Repetitive movements, obsession with routine, intense interest, and unusual reactions to sounds, light, textures, and smells are also common.
Autism begins early in development but may not be recognized until childhood or later into adulthood. This is a lifelong neurological difference that can present both challenges and strengths. Many people with autism exhibit beneficial qualities such as strong attention to detail, deep knowledge of areas of interest, logical thinking, creativity, and good memory.
Study author Livio Tarki and colleagues point out that previous research has shown consistent structural differences between the brains of people with autism and those of patients with neurotypical developmental disorders. The authors suggest that these differences may be related to the brain’s neurotransmitter systems. Neurotransmitters are chemical messengers that carry signals between brain cells. The researchers focused specifically on systems that use serotonin, dopamine, and glutamate.
Scientists investigated how differences in brain structure map to the spatial distribution of these chemical messengers. They analyzed data from the Autism Brain Imaging Data Exchange. This public dataset includes physical measurements, behavioral assessments, and brain scans collected at 20 different sites.
The data used in this analysis were obtained from 1,035 participants. The sample included 505 individuals with autism and 530 individuals with neurotypical development. The average age of participants was approximately 17 years. Both groups were predominantly male, reflecting historical diagnostic patterns.
The study authors used structural magnetic resonance imaging (MRI) data to calculate deviations from expected cortical thickness. Cortical thickness refers to the depth of the outer layer of the brain’s gray matter, which is responsible for complex thinking and sensory processing. They measured this thickness across thousands of individual points called vertices on the brain’s surface. These measurements were adjusted for both gender and age of each participant.
The researchers then compared these structural measurements to a reference map of neurotransmitter receptor density. Receptors are protein structures on cells that receive chemical messages. These reference maps were obtained from another previously published imaging study. This allowed the authors to see whether the areas of abnormal thickness in autism patients coincided with areas where certain neurotransmitters are known to be present in high concentrations.
The results showed that there was a wide range of deviations in cortical thickness in the brains of participants with autism compared to neurotypical participants. Structural differences tended to be greater in brain regions with higher serotonin receptor densities. The researchers did not find similar spatial associations for dopamine or glutamate receptors. At the individual level, greater deviations in cortical thickness were associated with greater difficulties in social and communication domains.
These findings provide evidence of a neurobiological link between autism, brain structure, and serotonin. However, the participants in this study were mostly male. Brain development and cortical thickness can vary by gender, so studies with more female participants may yield different results. Future research may help clarify these associations and guide support strategies tailored to people with autism.
The paper, “Autism and cortical thickness deviations from typical control: Evidence for a spatial association with serotonin receptors,” was authored by Livio Tarchi, Arne Doose, Julius Hennig, Fabio Bernardoni, Joseph A. King, Tiziana Pisano, Giovanni Castellini, Valdo Ricca, Inge Kamp-Becker, and Stefan Ehrlich.
