27 January 2016

On Russo's "Is there something unique about the transgender brain?": Well, yes and no.

In Scientific American Mind, journalist Francine Russo takes on a fascinating research question: “Is there something unique about the transgender brain?” She reviews some of the relevant brain research on transsexuals and concludes that transgenderism is indeed a phenomenon of the brain.  Although I agree with Russo that transgenderism is a phenomenon of the brain, I believe Russo over-focussed on gender identity, which led her away from the better explanation of the data:

These brain scans don’t reflect gender identity, they reflect sexual orientation.

The research that Russo examined she explained correctly: Biological males and females differ from each other on certain subtle, non-learned features of the brain and body, and some samples of transsexuals are in-between on these features.  That is, they were shifted away from what is typical for their sex-at-birth and towards the other sex.  Taken by itself, this would indeed seem like strong evidence that transsexuality in biological males is caused by having “feminine” or “feminized” features of the brain, and ditto for females/masculine/masculinized.

Unfortunately, Russo’s analysis excludes other, closely related research that would have led her to a different conclusion: Namely, gay men and lesbians show the same shifts! That is, the differences are not specific to transgenderism. For example, Russo pointed out (correctly) that males and females differ in “echolike sounds produced by the inner ear in response to a clicking noise” and that transgendered folks are shifted towards what the opposite sex usually shows. Missing, however, was the research showing that the same shift is present in cis-gendered homosexuality (e.g., McFadden & Pasanen, 1998). [For those interested, these echo-like responses are called “click-evoked otoacoustic emissions,” and the shift among transgendered folks was reported by Burke et al. (2014). The full reference appears below.]

The reason this matters is that, in the MRI study Russo describes (Zubiaurre-Elorza et al., 2013), all of the male-to-female transsexuals were attracted to men, but all of the control males were attracted to women, and all of the female-to-male transsexuals were attracted to women, but all the control females were attracted to men.  That is, although the subject groups differed from the control groups in their gender identity (as they must), they also differed in their sexual orientation. This is what we call a confound: We can’t know whether the brains of the male-to-female transsexuals differed from the controls because they wanted to be women while the controls wanted to be men, or because they were attracted to men while the controls were attracted to women (and ditto for female-to-male transsexuals with regard to men/women/women/men).

Although Russo attributes Zubiaurre-Elorza’s MRI findings to gender identity, those findings are better attributed to sexual orientation. This would have shown by other research that Russo excluded.  Specifically, Russo excluded other MRI studies of transsexuals, namely Rametti et al. (2010) and Savic and Arver (2010).  Rametti used a set-up very much like Zubiaurre-Elorza.  (In fact, Rametti and Zubiaurre-Elorza are from the same research team, led by Antonio Guillamon.) Rametti compared 18 male-to-female transsexuals who were attracted to men with: 19 cis-gendered control males who were attracted to women, and with 19 cis-gendered control females who were attracted to men. Guillamon contrasted the male controls with the female controls to find the features of the brain where males and females differ (there were six such features), and they found the transsexual group to be intermediate on all of them. That is, male-to-female transsexuals who were attracted to men were in between cis-gendered males who were attracted to women and cis-gendered females who were attracted to males.

Now, let us compare that with the Savic and Arver study: They also analyzed male-to-female transsexuals (24 in total), but these were male-to-female transsexuals who were attracted to women. Savic and Arver contrasted them with 24 control males who were attracted to women, and with 24 control females who were attracted to men. Like Rametti, Savic and Arver contrasted the male controls with the female controls to find the brain features where males and females differ (there were eight), but found the transsexual group to differ from the male controls on none (Savic & Arver, 2010, Table 3). In contrast with Rametti and with Savic and Arver, the transgendered bio males who were attracted to women did not differ from cis-gendered bio males who were attracted to women.  That is, what we’ve observed in the brain depends on whether the groups differ in sexual orientation, not gender identity.

Just as interestingly (if not more so!) the male-to-female transsexuals who were attracted to females did show other brain differences from the control males, but they were not features in which females differ from males. To me, this brings us to the next fascinating and unanswered question for us sexual neuroscientists: What is it about male-to-female transsexuals who are attracted to females that makes their brains different from other people’s, and is not just in between biological males and females?


References

Burke, S. M., Menks, W. M., Cohen-Kettenis, P. T., Klink, D. T. & Bakker, J. (2014). Click-evoked otoacoustic emissions in children and adolescents with gender identity disorder. Archives of Sexual Behavior, 43, 1515−1523. doi: 10.1007/s10508-014-0278-2.

McFadden, D., & Pasanen, E. G. (1998). Comparison of the auditory systems of heterosexuals and homosexuals: Click-evoked otoacoustic emissions. Proceedings of the National Academy of Sciences, 95, 2709–2713.

Rametti, G., Carrillo, B., Gómez-Gil, E., Junque, C., Zubiarre-Elorza, L., Segovia, S.,... Guillamon, A. (2010). The microstructure of white matter in male to female transsexuals before cross-sex hormonal treatment: A DTI study. Journal of Psychiatric Research. doi:10.1016/ j.jpsychires.2010.11.007.

Savic, I., & Arver, S. (2010). Sex dimorphism of the brain in male-to- female transsexuals. Cerebral Cortex. doi:10.1093/cercor/bhr032.

Zubiaurre-Elorza, L., Junque, C., Gómez-Gil, E., Segovia, S., Carrillo, B., Rametti, G., Guillamon, A. (2013). Cortical thickness in untreated transsexuals. Cerebral Cortex, 23, 2855−2862.


For professional researchers, see also:

Cantor, J. M. (2011). New MRI studies support the Blanchard typology of male-to-female transsexualism. Archives of Sexual Behavior, 40, 863864. doi: 10.1007/s10508-011-9805-6 http://link.springer.com/article/10.1007%2Fs10508-011-9805-6


12 comments:

  1. So the dimorphisms which reinforce gender socialization, will generally develop with an according sexual imprint. That the gynephilic M2Fs differ in what should be the imprinted fetish. And that so few of the fetishists are hyper-feminine homosexuals, gives credence to the "private vs public" psychological dynamics in the development of emasculation trauma.

    http://www.oocities.org/transsexual_analysis/transsexual5.html

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    1. A heterosexual male who is sexually attracted to females is not displaying a "fetish" as you suggest. Instead, he is quite normal.

      The term fetish has a very specific meaning, it is defined as "an object or bodily part whose real or fantasized presence is psychologically necessary for sexual gratification and that is an object of fixation to the extent that it may interfere with complete sexual expression".

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    2. That is correct. The more accurate word is "paraphilia," which includes the fetishes.

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    3. Technically speaking, all sexual desire is fetishistic, of fixation, of "objects", or presupposes some degree of necessity. I agree with an additional term being used to denote abnormality and another to denote unhealthy desire.

      Historically the term "fetish" has come to represent deviancy, all the while the phenomenological nature of the supposed normal is taken for granted. There is no given way in which bodies or sexual relations are constructed within experience, it is simply the case that one considers oneself deviant, on the basis of what they perceive the relevance of their desires, has towards human bodies, especially in the context of sexual intercourse. One thing is for sure, for phenomena to be arousing, it must associatively correspond with the phenomena on part of an erotic imprint. Perhaps we inherit some imprints, whilst some appear up until the end of puberty.

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  2. "What is it about male-to-female transsexuals who are attracted to females that makes their brains different from other people’s, and is not just in between biological males and females?"

    ANSWER: AUTISM

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  3. Interesting article, but you seem to be missing the nature paper by Zhou et al (1995) - investigating the BSTc in transgender individuals, homosexuals and heterosexual controls (incidently the best paper I've seen to date on the subject for how well it's controlled). In this study the BSTc of MTF transgender individuals was found to be consistent with that of control females (this region is typically larger in males than it is in females). Critically, this effect was seen independent of sexual orientation and was not affected by hormone treatment. This seems to go against your suggestion that transgender brain structure is simply a function of sexual orientation.

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    1. Sexual dimorphism of the BSTc occurs in adulthood, yet most transsexuals report dysphoria in childhood - see Kruijver et al., 2002.

      You should also know that in the Zhou study, the MTFs they examined had, in fact, received hormonal treatment.

      More recent scientific conclusions suggest that the Zhou findings did not accurately anticipate the effect of hormone therapy on the brain.

      See also: http://www.annelawrence.com/brain-sex_critique.html

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  4. "Sexual dimorphism of the BSTc occurs in adulthood, yet most transsexuals report dysphoria in childhood - see Kruijver et al., 2002."

    Sure, but it doesn't exclude the possibility that sexual dimorphism is manifested in more subtle ways in the BSTc in younger individuals.

    "You should also know that in the Zhou study, the MTFs they examined had, in fact, received hormonal treatment."

    Sorry, that should have read "BSTc volume was not found to be influenced by sex hormones in adulthood."

    "More recent scientific conclusions suggest that the Zhou findings did not accurately anticipate the effect of hormone therapy on the brain."

    Sorry, whose scientific conclusions? I just had a wee look at your link and it led me down a massive rabbit hole - there seems to be a lot of rebuttals and counter claims to the article and a quick google is telling me that lawrence appears to be a massively controversial figure which makes me think I should take all this with a pinch of salt before diving in!

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    1. --- " Sure, but it doesn't exclude the possibility that sexual dimorphism is manifested in more subtle ways in the BSTc in younger individuals."

      Sorry, it was the Chung study, not the Kruijver study.

      http://www.ncbi.nlm.nih.gov/pubmed/11826131

      From the article:

      "However, this difference became significant only in adulthood"

      Based on existing research, the BSTc in female and male children differ in /neither/ volume nor number of neurons.

      The further you lean toward "other possibilities," the further away you are moving from actual scientific conclusions.

      --- "Sorry, that should have read "BSTc volume was not found to be influenced by sex hormones in adulthood."

      If you read the Anne Lawrence article, you will see it explained in a very simple way that Zhou et al. were misguided in this conclusion. You could, alternativey, read the the Zhou article beyond the abstract. You would learn that:

      1) Every transsexual in the study had been receiving cross-sex hormones for a minimum of five years up to 20 years.
      2) They used, as controls, one male and one female (two people in total) who had NOT been given hormone treatments, but rather who had had tumors that had increased their cross-sex hormones to cross-sex levels, although not nearly as high as the levels that the transsexuals in the study would have been receiving. These individuals had these tumors for about one year.

      Based on these two pieces of information alone, in addition to the other scientific research on the effect of hormone treatment on the brain, regardless of WHO is saying it, it is extremely reasonable to conclude that there is a massive confound between gender identity and exposure to cross-sex hormones (both in terms of duration and dosage) wthin that study.

      --- "there seems to be a lot of rebuttals and counter claims to the article"

      There a total of three suggested explanations for Zhou's findings. Personally, I do not consider this to be a lot. This article is about the length of an undergraduate paper.


      ---"quick google is telling me that lawrence appears to be a massively controversial figure"

      The great thing about science is that an individual's personal ideology or social reputation does not inherently affect the veracity of any factual information they state. And to clarify, Anne Lawrence is stating facts - the actual scientific articles themselves are cited within the article, so you can personally verify if you desire. You can, instead, make the argument that the author is cherry-picking articles for presentation, but if you're familiar with brain sex research, you'll know that isn't all that feasible because there aren't a lot of articles to cherry pick from.

      Discounting a scientist's findings on the basis on the personal ideologies and not on a critical analysis of those findings negates the entire purpose of science. Water would still be H20 even if the person who had discovered it had been the most evil person ever born.

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  5. I believe that Anne Lawrence needs to be defended even more ardently. She is only "controversial" because she has researched and writes about a scientific theory about which many older transitioning MTF transsexuals would rather NO ONE researched or wrote about. Thus, as a person, she is NOT controversial... it is her position on a given topic that has made her unpopular, but NOT untrustworthy. Attempting to smear the messenger is not a valid scientific method.

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  6. Informative post with beautiful information. Thanks for sharing these information.

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  7. http://press.endocrine.org/doi/abs/10.1210/jcem.85.5.6564?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed

    "Therefore, we determined in 42 subjects the number of somatostatin-expressing neurons in the BSTc in relation to sex, sexual orientation, gender identity, and past or present hormonal status.

    ...point to a neurobiological basis of gender identity disorder."

    http://www.nature.com/nature/journal/v378/n6552/abs/378068a0.html

    "Here we show that the volume of the central subdivision of the bed nucleus of the stria terminalis (BSTc), a brain area that is essential for sexual behaviour3,4, is larger in men than in women. A female-sized BSTc was found in male-to-female transsexuals. The size of the BSTc was not influenced by sex hormones in adulthood and was independent of sexual orientation."

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