August 7, 2013

Transgender Brains Are Different!

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. I’ve also seen people say that it’s all bunkum and that transgender is purely in the mind but not in the brain. Who was right?

The “X part of the brain is like a woman’s” may have had its genesis in Zhou, et al., “A Sex Difference in the Human Brain and its Relation to Transsexuality” (1997). [At least, it’s the earliest study I was able to identify.] 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. A follow-up study by Krujiver et al (2000), [a study that included all four doctors from Zhou] attempted 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.

So, are trans brains different? The cited studies indicate that they are. Of four areas of the brain studied, three of those four areas the trans brain better matched the gender identity rather than the assigned gender (and the fourth suggested a difference from both cisgenders). It hasn’t been proven that trans brains are “different than” their cisginder counterparts or “more like” the cisgender they perceive themselves to be, because in science proof is a dirty word. This is a collection of evidence that supports the hypothesis that there are differences in the trans brain that may account for gender dysphoria. It’s interesting and tantalizing science, for sure, and it suggests that anyone viewing gender dysphoria as “just a mental disorder” hasn’t considered all the available data. 

[This is partially reblogged from Ali Finds Her Self, my personal blog. I have updated and edited it for Transgender Science.]

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