A new study has revealed that long-term testosterone therapy, such as that given during a female-to-male transition, changes a patient’s brain structure to enable them to literally “think” like a man. The study not only adds further support to the idea that men and women process information differently, but also sheds light onto the significant effect that hormones have on human appearance and behavior.

For ethical reasons, it has been difficult to properly study the long-term effect of hormone treatments. However, in a study presented today at the European College of Neuropsychopharmacology (ECNP) Congress in Amsterdam, researchers from Vienna and Amsterdam had the opportunity to work with 18 female-to-male transsexuals. The patients were a mean age of 27 and had all received high-dose testosterone treatment. According to the press release, the patients were given MRI brain scans both before their treatment and again four weeks after the testosterone administration. Blood samples were also taken during each MRI session to identify associations between the testosterone in the body and the brain scans.

Results revealed real measurable differences in brain structure following exposure to testosterone treatment. For example, the scans revealed that the treatment had decreased the volume of gray matter in two specific language-related areas of the brain: the Broca’s and Wernicke's areas. The scans also showed that, while the physical volume of these two areas decreased in size, the white matter pathways connecting the areas got stronger.

According to Dr. Andreas Hahn, a researcher involved with the study, the decrease in gray matter size after receiving testosterone corroborates previous research that has linked higher testosterone levels in children to smaller vocabularies. However, the strengthening of white matter is something the scientists had not expected. “We think that when it comes to certain language skills, the loss of gray matter outweighs the strengthened white matter connection,” Hahn explained in a statement.

The findings suggest that testosterone treatment plays an important role in female-to-male transitions, by enabling patients to not only look more masculine, but also think in a more masculine manner. Hormones are regulatory substances produced by the body to help stimulate specific body functions. Among its many uses, the sex hormone testosterone is often given to transgender men in an effort to help their body take on more masculine features. The most obvious effects of testosterone treatment are those that can be easily observed, such as a deeper voice, increased body hair, rearrangement of body fat distribution, and an increase in acne. However, testosterone also causes subtle but equally significant body changes. For example, testosterone treatment can also cause psychological changes, such as mood swings, anxiety, and agitation.

As suggested by the results of this study, hormones may also play a key role in human development — and the differences in sex hormone levels may explain why women often have stronger communication skills than men.

Source: Hahn A, et al. Testosterone changes brain structures in female-to-male transsexuals. 28th European College of Neuropsychopharmacology Congress. 2015