May 14, 2013

Transsexual Brains Are Different

magnus_pyke_scienceSo, I got on a “brain” kick recently. It started with the question, “How is HRT going to affect my brain?” But I realized that before I could even look at that question, I had to find the answer to another question first: Are the brains of transgender people different than those of cispeople?

I’ve heard lots of things said about the transgender brain — that this or that part of it is bigger, or smaller, or more like the opposite gender. Some people online insist that the MtF brain is female, not male. I’ve also read other people say that it’s all bunkum and that transgender is purely in the mind but not in the brain. Who was right? I looked to science for an answer.

As it turns out, the “X part of the brain is like a woman’s” appears to have its genesis in Zhou, et al. (1997). This study measured the the bed nucleus of the stria terminalis (BSTc), a part of the brain that (a) is involved in sexual behavior, (b) is sexually dimorphic (i.e. different in males and females), and (c) is not known to be affected morphologically by estrogen or testosterone (i.e. hormonal levels don’t affect its size). They found that the BSTc of MtF transsexuals were the size of a cisfemale’s BSTc, suggesting that the brain of a transsexual has some attributes that are female.

[As a quick usage note: all of these studies used the term transsexual rather than transgender. I’ve picked up on their usage just for consistency.]

A second study, Krujiver et al (2000), [a study that included all four doctors from Zhou] followed up on the 1997 Zhou study, this time attempting to determine whether the actual neurons in the BSTc of MtF transsexuals match those of cisfemales. They did, which not only supported the findings of the earlier study but also lent strong support to the notion that transsexuality is more than just a mental illness.

In 2008, one of the scientists from the prior two studies (whose name is, I kid you not, Dick Swabb [yes, I have the sense of humor of a five year old]) looked into another sexually dimorphic, morphologically unaffected part of this brain, this time the hypothalamic uncinate nucleus. Garcia-Falqueras & Swabb (2006) found, once again, that the MtF brain resembled the cisfemale brain and not the cismale brain in this structure.  They also found that the brain of a single FtM subject more closely matched the cismale brain.

When most people (and all zombies) think of brains, however, they don’t think about small, obscure structures. They think about the grey matter. Luders, et al. (2009) looked at that, too, using 24 pre-HRT MtF transsexuals and 60 cis control subjects (30 male, 30 female). They found that the grey matter variance in the transsexuals in fact matched the cismen more than the ciswomen (a finding further supported by Savic & Arver [2011]). One exception was in an area called the right putamen, which was notably larger in the MtFs than in the cismen.

More recently, Rametti, et al. (2011) studied the white matter of the brains of pre-HRT FtM transsexuals and compared them to a control group of cismen and ciswomen. They found that the white matter in the FtMs matched the cismale control to a high degree, even though they were pre-HRT.

That’s four areas of the brain that have been studied, and in three of those four areas the brain of the transsexual better matched the gender they identified with rather than the gender they were born into (and the fourth suggested a difference from cisgender). Does this mean that it’s been proven that transsexual brains are “different than” their cisginder counterparts or “more like” the cisgender they perceive themselves to be?

No, because in science proof is a dirty word. This is a collection of evidence that supports the hypothesis that there are differences in the brain of the transsexual that may account for gender dysphoria. It’s interesting and tantalizing science, for sure, and it suggests that anyone viewing transgenderism as “just a mental disorder” hasn’t considered all the available data.

So that’s part one of all this. Once I sorted all that out, I was able to get to the question I was originally pursuing: what are hormones going to do to my brain when I start taking them? Part two, coming soon …


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