A quarterly publication of the Autism Research Institute

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

Fall, 2018 | Number 4, Volume 32

Large-scale study in Britain provides strong support for “extreme male brain” theory of autism

A new study involving more than half a million people offers strong support for the “extreme male brain” theory of autism. 

The study, by David Greenberg and colleagues, including Simon Baron-Cohen, explored two theories originated by BaronCohen: 

• The empathizing-systemizing theory predicts that men will score higher on tests of systemizing—that is, the drive to analyze and to build rule-based systems—while women will score higher on tests of empathizing, or the ability to recognize other people’s thoughts and feelings and the drive to respond to them with an appropriate emotion. 

• The extreme male brain theory predicts that on average, people with autism will show a masculine shift compared to the general population, scoring equally high or higher on systemizing and lower on empathizing. 

In conjunction with the British television production company Channel 4, the researchers tested more than half a million people, including more than 36,000 people with autism. Using brief measures of empathy, systemizing, and autistic traits, they confirmed that in the general population, women typically scored higher than men on empathizing, and men typically scored higher on both systemizing and autistic traits. Individuals with autism had “masculinized” scores, scoring higher on systemizing and lower on empathizing compared to the typical population. The researchers validated their findings in a second sample of more than 14,000 people. The researchers also calculated the difference between each individual’s score on the systemizing and empathizing tests (the “d-score”). A high d-score indicates that a person’s systemizing is higher than his or her empathy, while a low d-score indicates the opposite. In the general population, men typically had a shift toward a high d-score, while women typically had a shift toward a low d-score. Individuals with autism typically had a shift toward an even higher d-score than males in the general population. The researchers note that d-scores accounted for 19 times the variance in autistic traits compared to other demographic variables, including sex. 

The researchers say both males and females with ASD exhibited a masculinized shift. “This has relevance for understanding the etiology of autism, implicating a biological mechanism involved in neural sexual dimorphism,” they say. “The extreme male brain theory is in line with brain imaging studies which find that autistic females are masculinized in both brain structure and function.” In addition, they say, the theory is consistent with studies showing elevated prenatal sex steroids in ASD as well as elevated circulating sex steroids and elevated rates of polycystic ovary syndrome in females with autism (see related story on page 6). 

The researchers emphasize that their findings apply to group averages, not to individuals, and apply only to two gender-related traits—systemizing and empathizing—and not to traits such as aggression. In addition, they note that while individuals with autism often have difficulty recognizing other people’s thoughts and feelings (“cognitive” empathy), they have intact “affective” empathy—that is, the ability to care about others. “Difficulties with cognitive empathy tend to lead autistic people to avoid or be confused by social situations, rather than to act with cruelty,” they say. 

Baron-Cohen comments, “This research… pinpoints some of the qualities autistic people bring to neurodiversity. They are, on average, strong systemizers, meaning they have excellent pattern recognition skills, excellent attention to detail, and an aptitude in understanding how things work. We must support their talents so they achieve their potential—and society benefits too.”


Citations

“Testing the Empathizing-Systemizing theory of sex differences and the Extreme Male Brain theory of autism in half a million people,” David M. Greenberg, Varun Warrier, Carrie Allison, and Simon Baron-Cohen, Proceedings of the National Academy of Sciences, November 12, 2018 (free online). Address: David Greenberg,  [email protected]

—and—

 “Over half a million people take part in largest ever study of psychological sex differences and autistic traits,” news release, University of Cambridge, November 2018.