Popular testosterone therapy given to women undergoing sex change can make them think more like men after the treatment, a unique study has suggested.
The results show that this therapy induces structural changes in areas of the brain involved in verbal fluency in female-to-male transsexuals.
Their brains undergo structural changes and shrink in areas that play a key role in language, the team from Vienna and Amsterdam found.
It has been known for some time that higher testosterone is linked to smaller vocabulary in children and that verbal fluency skills decrease in female-to-male transsexuals after testosterone treatment.
"What we see is a real quantitative difference in brain structure after prolonged exposure to testosterone. This would have been impossible to understand without looking at a transsexual population," said professor Rupert Lanzenberger from University of Vienna, Austria.
Brain imaging shows that testosterone therapy given as part of sex reassignment changes the brain structures and the pathway associated with speech and verbal fluency.
This result supports research that women in general may deal with speech and interaction differently than men.
Previous studies have shown that testosterone has a particular influence on verbal fluency.
For the new study, the researchers worked with 18 female-to-male subjects before and during testosterone treatment.
The subjects underwent MRI brain scans before and after four weeks of the testosterone administration.
The results showed that with testosterone treatment the volume of grey matter decreased in two specific regions of the brain which are mainly responsible for language processing.
At the same time, the neuronal pathway (white matter) connecting these two regions via the extreme capsule got stronger.
"This fits in well with our finding of decreased grey matter volume," added Dr Andreas Hahn from University of Vienna.
However, the strengthening of the white matter in these areas was a surprise.
"We think that when it comes to certain language skills, the loss of grey matter outweighs the strengthened white matter connection," Dr Hahn explained.
This may have wider implications, for example in the way that men and women handle speech and interaction.
"In particular, female-to-male gender reassignment resulted in local brain matter decrease within language processing regions, which may explain why verbal abilities are often stronger in women," noted Dr Kamilla Miskowiak from Copenhagen University Hospital.
The research was shared at the annual meeting of the European College of Neuropsychopharmacology (ECNP) in Amsterdam, the Netherlands.