It’s long been known that autism is far more prevalent in males than in females. What hasn’t been understood is why. “Of course, the primary suspect when we have something that is sharply differentiated by sex is testosterone,” says Gideon Nave, an assistant professor of marketing in Penn’s Wharton School. Yet a new study led by Nave implores scientists to keep looking.
In two randomize control studies of testosterone administration which were the largest of their kind and include nearly 650 men, Nave and colleagues found no evidence of a link with cognitive empathy, the capacity to read the emotions of others, a trait that is characteristically impaired in people with autism. They report their findings in the journal Proceedings of the Royal Society B: Biological Sciences.
Test of reading emotions
“Several earlier studies have suggest a connection between testosterone and reduce cognitive empathy; but samples were very small, and it’s very difficult to determine a direct link,” says Amos Nadler of Western University; also the first author of the study. “Our results unequivocally show that there is not a linear causal relation between testosterone exposure and cognitive empathy.”
Prior to this work, the strongest evidence for a link between testosterone exposure reduce cognitive empathy; hence came in 2011 in a study that find administering testosterone to healthy women reduce their performance on a test of reading emotions. The results suggest the testosterone impair their performance. Moreover, the work point to the ratio of the length of the participant’s second finger to their fourth finger; hence known as the 2-D:4-D ratio, as a proxy for sensitivity to testosterone.
Some believe that the ratio declines with increase in utero exposure to testosterone though evidence for that connection is mix. That study’s authors contend that their findings support the idea that prenatal testosterone exposure create a more masculinize brain that less readily infer the emotional state of others. The study was use as support for the “extreme male brain” hypothesis of autism; which contends that autism is an exaggeration of “male” tendencies toward a cognitive style characterize by systemizing over empathizing.
Testosterone administration affect
Participants were then show a photo of an actor’s eyes; also ask to select the emotional state that best describe their expression. All participants also had their 2-D:4-D ratio measured. While the testosterone gel did increase participants’ levels of the hormone; so the researchers find no evidence that testosterone administration affect performance on tests of cognitive empathy. They also find no relationship between participants’ performance on the tests and their 2-D:4-D ratio.
“The results are plain,” says Nave. “However, it’s important to note that the absence of evidence is not evidence of absence. We found that there is no evidence to support this effect of testosterone; but that doesn’t rule out any possible effects. From what we know, though, it seems that if testosterone does have an influence; so the effect is complex, not linear. Reality is typically not that simple.”
And the new study includes more participants than the earlier one by almost two orders of magnitude; augmenting the researchers’ confidence in the results. The extreme male brain theory of autism has receive a lot of attention but, Nave notes, “if you look at the literature carefully; there is still not really strong support for it. “For now, They think we have to embrace our ignorance on this.”