For the first time, the brain structure of male-to-female transsexuals has been investigated in living individuals using MRI brain scans, helping to fuel the debate over the possible neural basis of gender identity.
The scientific article, shortly to appear in the neuroscience journal NeuroImage, used MRI brain scans and a technique called voxel based morphometry to compare grey matter in a group of male-to-female transexuals to groups of males and females who have never had gender-identity concerns.
This is not the first time that brain structure has been compared in this way, but earlier studies had been based on post-mortem comparisons. These three studies had found that certain areas in male-to-female transsexuals more commonly resembled the equivalent area in females than males.
This has led some researchers to go as far as suggesting that perhaps the differences are present from birth and that gender-identity difficulties could result from the body and brain following different paths as the developing foetus begins to develop into a specific sex.
However, one difficulty is that all the transgender people examined in these post-mortem studies had been on oestrogen treatment to feminize their bodies, and it hasn’t been clear whether the differences were due to the effect of this hormone rather than something present before.
This new study, led by neuroscientist Eileen Luders, specifically recruited male-to-female transsexuals who had never taken oestrogen and, being in living people, wasn’t affected by whatever led to the person’s death.
In contrast to previous investigations, this new study found that male-to-female transsexuals grey-matter was similar in most areas of the brain to the male rather than female comparison group.
Except, that is, for one area, the putamen, a deep brain structure that forms part of the basal ganglia – known for its wide range of functions and connections to the frontal lobes and action control areas.
Because we know so little about the neuroscience of self-image and gender-identity it’s almost impossible to draw any conclusions for the fact that this specific area seems more ‘feminine’, or that the majority of the other areas seem more ‘masculine’ in terms of size.
What this study does do, however, is add to the increasing evidence that there are some detectable neurological differences in the brains of transgendered people. We’re just not in a position to say much about the significance of this yet.
Link to PubMed entry for ‘in press’ paper.