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.

For this study, researchers took brain scans of 18 subjects before and after their testosterone treatments. After the treatment, the levels of gray matter in Broca’s and Wernicke’s areas, two brain regions that process language, decreased, while the white matter connecting the two regions increased. One of the study authors, Andreas Hahn of the Medical University of Vienna, speculated that the reduction in the gray matter outweighed the strengthening of the connections.