The unfortunate thing about studies on the differences between male and female brains is that they get overstated in ways that perpetuate stereotypes. (“Women are better at nurturing, so why don’t you bring the cupcakes?”)

The unfortunate thing about stereotypes is that there’s sometimes a grain of truth at their center that gets distorted to the point of nonsense. The myth is that women are, overall, more “verbal” than men are. The truth is that both genders utter about 16,000 words per day, but grown women do seem to talk more than men do in certain contexts. In childhood, girls tend to speak earlier and with more complexity than boys do, and boys born with high levels of testosterone in their blood are more likely to have speech delays.

That’s left scientists hunting for the reasons why: Is it socialization, or differences in a so-called “language protein” in the brain, or in how the body processes testosterone?

A brain-imaging study out today from the European College of Neuropsychopharmacology supports the theory that it might be testosterone that explains how men and women, on average, handle speech and social interactions differently.

Some past studies have shown that testosterone dampens talkativeness. But researchers have been limited by the fact that they couldn’t administer extra testosterone to otherwise-healthy people. A group of female-to-male transgender people, meanwhile, offered a unique opportunity to study the effects of testosterone on the brain, since these individuals were voluntarily taking high doses of testosterone in order to assume more masculine traits.