A quarterly publication of the Autism Research Institute

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

Fall, 2019 | Number 4, Volume 33

Researchers question “extreme male brain” theory of autism

The extreme male brain theory of autism, first advanced by Simon Baron-Cohen, proposes that elevated prenatal exposure to androgens (“male” hormones) masculinizes the developing brain, leading to reductions in empathy. A new large-scale study casts doubt on the theory, but some researchers are questioning the validity of the study’s findings. 

The study by Amos Nadler and colleagues involved two groups of neurotypical men. In the first part of the study, 243 men who received either transdermal testosterone gel or a placebo completed a test called the “Reading the Mind in the Eyes Test” (RMET). In the second part of the study, 400 men completed the RMET after receiving either nasal testosterone gel or a placebo. 

The researchers also measured all participants’ 2D:4D ratio—that is, the relative lengths of the index and ring fingers. In both men and people with autism, the ring finger tends to be longer than the index finger, and researchers speculate that this is due to prenatal exposure to testosterone. 

The researchers detected no effect of testosterone administration on RMET scores. In addition, they say, there was no relationship between RMET scores and 2D:4D ratio. Nadler concludes, “Our results unequivocally show that there is not a linear causal relation between testosterone exposure and cognitive empathy.” 

However, researcher Punit Shah—who was not a part of the study—argues that “there is a critical flaw in the study which undermines the authors’ conclusions. The authors used a so-called ‘empathy test’ that is not a test of empathy at all. The RMET, as used by the authors, has recently been found to be a measure of emotion processing or even just a vocabulary test as it involves knowledge of complex words.” 

Baron-Cohen also questioned the findings because all of the participants were male rather than female. To detect an effect of testosterone, he argues, it is necessary to study people whose baseline levels are relatively low.


Citations

“Does testosterone impair men’s cognitive empathy? Evidence from two large-scale randomized controlled trials,” Amos Nadler, Colin F. Camerer, David T. Zava, Triana L. Ortiz, Neil V. Watson, Justin M. Carré, and Gideon Nave, Proceedings of the Royal Society B, August 12, 2019 (free online). Address: Gideon Nave,  [email protected]

—and—

 “Extreme male brain theory of autism overturned as huge study finds no link between testosterone and lack of empathy,” Kashmira Gander, Newsweek, August 3, 2019. 

—and—

 “Study challenges idea that autism is caused by an overly masculine brain,” Emily Underwood, Science, September 3, 2019.