A new study found that the brain’s language centers shrank in female-to-male transsexuals after they began testosterone treatment, but those conclusions are being questioned
Is testosterone, or the lack of it, the reason women perform better on tests of language skills than men?
Or is the enhanced verbal performance due to social factors as opposed to biology?
New research that looked at the effects of testosterone on trans men is trying to answer that question.
There aren’t definitive results yet, but the researchers’ conclusions on language skills and testosterone, if nothing else, have people talking.
The study, presented at the 28th European College of Neuropsychopharmacology Congress, followed 18 female-to-male transsexual subjects in their late 20s and early 30s as they began testosterone treatments.
The researchers examined the subjects before they began taking testosterone and then again after four weeks. They measured how much testosterone was in each subject’s blood and tracked these levels against brain activity measured using magnetic resonance imaging (MRI).
At the four-week follow-up, the subjects showed reduced gray matter volume, which is the material in the brain that makes up its computing nodes. Specifically, the shrinkage occurred in Broca’s area and Wernicke’s area, two regions of the brain that are involved with language processing and comprehension.
The higher the subjects’ blood testosterone levels, the more these regions shrank, researchers said.
On the other hand, the white matter that forms the connective bridge between the two brain areas grew stronger and more active as the testosterone levels rose higher.
So what does this mean?
According to the study’s lead author, Andreas Hahn, Ph.D., these findings may explain why women often display better language abilities than men.
“We feel that our findings may establish a link that the hormone-dependent sex differences of certain language skills like verbal fluency can be explained by changes in the corresponding language-specific brain structures,” explained Hahn, a postdoctoral researcher at the Department of Psychiatry and Psychotherapy at the Medical University of Vienna, Austria, in an interview with Healthline.
Hahn didn’t measure the subjects’ verbal skills. Instead, he’s extrapolating from past research that has linked testosterone levels with language ability.
According to Lise Eliot, Ph.D., associate professor of neuroscience at the Chicago Medical School at Rosalind Franklin University, this body of research is questionable and its findings muddled.
“The data are all over the map with regard to testosterone’s effect, positive or negative, on verbal and spatial skills,” she said. “Some [studies] show higher testosterone levels associated with better spatial performance, some find moderate levels are the best, some report spatial skills worsen the higher the testosterone level, and several find no relationship between testosterone levels and various cognitive skills. [One study Hahn cited] is exactly the one that failed to reproduce [its results] within the same lab.”
Instead, Eliot argues in her book Pink Brain, Blue Brain that differences in verbal ability between men and women are the result of social conditioning.
Studies that have found underlying brain differences show size differences far smaller than the performance gap on cognitive tests. And they don’t even come close to explaining the gender gap in people who work in science and math-related fields.
Eliot is also concerned about the strength of Hahn’s study in particular.
“This article is filled with confirmation bias,” she said. “It dramatically overstates findings about testosterone effect on brain structure [and] function. There is [also] likely to be some placebo effect involved, since the participants know they are taking testosterone. Finally, any neural changes after testosterone exposure could also result from the new experience of living as a male.”
Eliot supplied Healthline with her own wealth of studies challenging the idea that trans men’s brains are biologically most similar to cisgender men’s.
“Gender is a spectrum, whereas the social labels we apply to gender are binary,” she said.
Instead, she contends that trans men have brains similar to cisgender women, and vice versa.
“The vast majority of neuroimaging studies (including our own) indicate that transsexual subjects exhibit brain characteristics in between their biological and the identified gender,” he argued.
Eliot isn’t buying it.
For that to be the case, there would have to be clear differences between male and female brains in the first place. And she disputes the notion that brains can be described as male or female at all.
“My interpretation of this muddle is that there is no such thing as a ‘male brain’ and ‘female brain,’” Eliot explained. “Brains are intersex, meaning you will find far more overlap than difference between genders for any of the measures that have been found to differ statistically between males and females. It’s like the difference between a male kidney and female kidney, rather than the difference between an ovary and a testis.”
Hahn, however, thinks the differences are important.
“We totally agree with the point that there is far more overlap than difference between male and female brains,” he said. “Still, we would like to mention that there is also a marked difference in the prevalence of psychiatric disorders between men and women, which may be explained to some extent by sex hormones.”
Women are at greater risk for depression, anxiety, and eating disorders while men are more likely to experience addiction and antisocial personality disorder. And it’s important to study sex differences in psychiatry, Hahn explains.
“Various pharmacological treatment agents have been tested only for men and results are then extrapolated to women,” he said. “In this respect, we feel that it is important to study sex differences of the human brain and investigate the corresponding influence of circulating sex hormones.”
Eliot is dubious that psychiatric differences can be explained by biological causes.
“The different prevalence of psychiatric disorders between males and females could be due to differences in gonadal hormone levels, but this has never been demonstrated,” she said. “They could also be due to social role development.”
For example, she said, anorexia nervosa is 10 times more prevalent in females but only in cultures that value skinny women.
In addition, depression and anxiety are more prevalent among people with low social power, such as women. Those with higher social power react to adversity with other psychiatric disorders, such as conduct disorder/aggression or drug addiction.
“I looked carefully at the data on depression onset at puberty and it is simply not well-correlated with estrogen levels,” said Eliot. “Nor have researchers been able to clearly document a relationship between depression and hormonal changes at menopause.”
The take-home message? An oldie, but goodie: More research is needed.
“It’s hard to compare studies with opposite findings until someone does meta-analysis,” concluded Eliot.