A quarterly publication of the Autism Research Institute

The Autism Research Review International is quarterly publication of the Autism Research Institute

Summer, 2021 | Number 3, Volume 35

“Extreme male brain” theory investigated

According to the “extreme male brain” theory of autism, individuals with autism spectrum disorders (ASD) have a masculinized brain. However, a new study indicates that the reality may be more complex. 

ASD is much more common in males than females, and studies indicate that it is associated with behaviors considered typical for males. Study coauthor Liza van Eijk notes, “Men score on average lower on empathy tasks than women, while adults with ASD, irrespective of their sex, score the lowest. Conversely, men score on average higher than women on an attention-to-detail task, while individuals with ASD score the highest.” 

To explore variations in brain structure that might shed light on these differences, van Eijk and colleague Brendan Zietsch developed a data-derived measure of individual differences in subcortical brain shape along a male-female continuum. They then used this tool to analyze data from 1,060 individuals with ASD and 1,166 neurotypical individuals, in order to determine the “maleness” of their brains.

“Consistent with the extreme male brain hypothesis,” van Eijk says, “we found a higher mean brain maleness score in the ASD group than in controls.” In addition, brain “maleness” scores were positively associated with autistic symptoms. 

However, the researchers considered that their finding might be due to the larger brain size in the ASD group. “Indeed,” they say, “after adjusting for differences in brain size, the brain maleness difference between the ASD group and controls disappeared, and no association with autistic symptoms remained… suggesting greater maleness of the autistic brain is driven by brain size.”


Citations

“Testing the extreme male brain hypothesis: Is autism spectrum disorder associated with a more male-typical brain?”, Liza van Eijk and Brendan P. Zietsch, Autism Research, May 19, 2021 (online). Address: Liza van Eijk, Department of Psychology, College of Healthcare Sciences, Division of Tropical Health and Medicine, James Cook University, Douglas, QLD, Australia, [email protected]

—and— 

“Is autism linked to a more ‘male’ brain?”, news release, James Cook University, June 16, 2021.