A large-scale MRI study has observed that the brains in people with autism spectrum disorder show fewer differences between the two hemispheres. Headed by a team from the Max Planck and Donders institutes, Nijmegen, the Netherlands, and the University of Southern California, the international team found differences in brain asymmetry between people who had autism and those who did not, mainly affecting gray matter thickness in multiple regions of the brain.
The first author of the study, Merel Postona, explains that prior studies have suggested that people who have autism spectrum disorder are less prone to have the usual asymmetries for hand preference or language dominance. Nonetheless, it has been unclear if the asymmetry of the brain’s anatomy is affected by autism, as different studies have different results.
The right and left hemispheres of our brains develop differently because each hemisphere is responsible for particular functions. For instance, for most people, the left hemisphere, which controls the right hand, is dominant for language, although brain asymmetry may sometimes be affected in people who suffer from psychiatric or developmental disorders such as autism, which is symptomized by impaired social cognition, repetitive behavior and restricted interests. Scientists belonging to the international ENIGMA consortium of brain researchers undertook the large-scale study, using brain scans collected from different countries over two decades. This research is the largest study of this magnitude that used brain scan data from 1,774 people on the spectrum as well as 1,809 healthy controls.
The team observed that the left and right cerebral hemispheres of the brain are more similar to each other in people with autism, implying that people with ASD had less brain asymmetry. The lower asymmetry was mostly found for cortical thickness at several locations on the brain’s surface. In a healthy brain, the cerebral cortex’s thickness lies is different between the right and the left hemispheres. The anatomical differences were independent of IQ, sex, age, medication use, or the severity of symptoms.
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