Regional Grey Matter Structure Differences between Transsexuals and Healthy Controls—A Voxel Based Morphometry Study – Review

This is a study with intriguing results. The study also has some frustrating flaws.

One of the most interesting things about the study is this:

“The regions found affected in our study are mainly involved in neural networks playing role in body perception, including memory retrieval, self-awareness, visual processing, body and face recognition and sensorimotor functions.”

In other words, gender dysphoria may be linked in some way to body perception.

The study found three types of differences in the brain:

In some areas of the brain trans people had less gray matter than cis people. This suggests that gender dysphoria might be caused in part by differences in body perception – or that gender dysphoria changes areas of the brain related to body perception.

In some areas biological males had more gray matter, in some areas biological females had more gray matter. Males generally have a larger volume of gray matter than females. Other studies have found regions where females have a larger volume of gray matter and regions where males have a larger volume, but there doesn’t seem to be an accepted map of which regions are which yet.

In some areas of the brain the trans people had gray matter volumes that were more like controls of the same sexual orientation and gender identity.

So the biggest flaw of the study is that they don’t control for sexual orientation.

Instead they specifically selected trans people who were attracted to members of their biological sex and then chose controls who shared their age and gender identity.

The authors do not discuss the sexual orientation of the control group, but 95% of the population is attracted to the opposite sex.

Thus, as in a number of other studies,* when the authors compare trans men (born female) to control females, they are comparing a group of people attracted to females to a group of people attracted to males. And when they compare the trans men to control males, they are comparing two groups of people attracted to women.

We know that sexual orientation can affect brain anatomy, so we can’t be sure if we are seeing differences due to gender identity or to sexual orientation.

Studies of gender identity need to start including some gay and lesbian cis people in their control groups.

In addition, if we keep leaving out trans people based on their sexual orientation, we are not properly studying gender dysphoria. About half of all trans women are attracted to females; we can’t just ignore them. We need to understand their brains, too.

A couple of other flaws:

1. The authors never discuss the sex differences they found. What do they mean? Do biological males and females process information about their body differently? How are these differences related to the differences between people with a female or male gender identity?

2. The authors don’t say whether or not they controlled for depression. Depression generally seems to decrease the volume of gray matter in the brain. The control subjects were screened to make sure they had no psychiatric disorders. Psychiatric data was collected on the people with gender dysphoria, but they don’t say if they excluded any trans people with psychiatric disorders like depression.**

People with gender dysphoria are more likely to be depressed than the general population. Since the results of the study involve the volume of gray matter in the brain, it would be important to control for depression – and possibly anxiety, etc.

In short – this study found an intriguing link between gender dysphoria and gray matter volume in areas of the brain that are related to body perception. They found some areas of the brain where trans people and cis people differ. They found some areas of the brain where people with gender dysphoria may be more like people who share their gender identity rather than their biological sex, BUT since they also shared the same sexual orientation, we can’t be sure. In addition, the study found a number of areas where biological sex was more important than gender identity. Finally, it is not clear if they controlled for depression and anxiety which could also have affected their results.

This is part I of my review. I will address specifics of the study in a future article or articles.

Original Article:

Regional Grey Matter Structure Differences between Transsexuals and Healthy Controls – A Voxel Based Morphometry Study by Lajos Simon, Lajos R. Kozák, Viktória Simon mail, Pál Czobor, Zsolt Unoka, Ádám Szabó, Gábor Csukly in PLOS one, December 31, 2013. 


*This is not the first study of gender identity and the brain to look only at trans people who were sexually attracted to their birth sex. See also, here and here. I think there are more studies that do this that I haven’t reviewed yet.

This study found that trans women’s brains were more like male controls than females; I think that the people doing these studies are trying to avoid a similar result by only looking at trans people who are attracted to their birth sex.

Except that doing this means they may be studying sexual orientation, not gender identity.

It also means that they don’t know if the brains of trans people attracted to their birth sex actually are different from the brains of trans people who aren’t attracted to their birth sex because, damn it, they aren’t looking!

** The authors say they excluded people with gender dysphoria from the study if they a) were “nonhomosexual,” b) had previously taken hormones, c) had a known chromosomal or hormonal disorder, or d) had a neurological disorder. In addition, when patients were diagnosed with gender dysphoria, they were assessed for psychiatric problems in order to “exclude the presence of other mental disorder behind the symptoms of GID.” (GID=gender identity disorder=the older name for gender dysphoria.) Depression would not rule out gender dysphoria, however. It looks like patients with both gender dysphoria and depression could have been included in this study.