The atypical brain development of transsexuals

ENG_trans.jpgTranssexuals are convinced that they were born in the body of the opposite gender and would do almost anything to change that fact. This transformation occurs step by step, by first taking on the social role of the other gender, then taking hormones and then undergoing a series of major operations, after which just 0.4 percent express regret later.

The gender team of the Vrije Universiteit Medical Centre in Amsterdam has been a pioneer in this field for many years, initially under the leadership of professor Louis Gooren and now of professor Peggy Cohen-Kettenis. This is unusual because the Bible, on which the VU is founded, states in Deuteronomy 22:5-6: “A woman must not wear men’s clothing, nor a man wear women’s clothing, for the Lord your God detests anyone who does this.”

In the womb

Male-to-female (M2F) transsexuality occurs in 1 in 10,000 men, and female-to-male (F2M) transsexuality in 1 in 30,000 women. Gender problems are often expressed early in development. Mothers describe how from the moment their son could talk, he would wear his mother’s clothes and shoes, he was exclusively interested in girls’ toys and mostly played with girls. But not all children with gender problems want to change gender later. If necessary, puberty can be delayed for a while with a hormone inhibitor to gain additional time to make a decision about whether to undergo treatment or not.

All of the data indicate that gender problems develop in the womb. Small changes have been found in genes involved in the effect of hormones on brain development, which increase the chance of transsexuality developing. Abnormal hormone levels in the fetus in the womb and medicines that the mother takes during pregnancy that disturb the breakdown of sex hormones can increase the chance of transsexuality developing.

Sexual differentiation of our genitalia occurs in the first few months of pregnancy while sexual differentiation of the brain takes place in the second half of pregnancy. As these two processes occur at different times, it is theorised that in transsexuality these processes are influenced independently of each other. If that hypothesis is true, then we would expect female structures in the male brains of M2F transsexuals and vice versa in F2M transsexuals.

Brain and hormones

In 1995 such a reversal of the gender difference was published by us in Nature. It involved the bed nucleus of the stria terminalis (BSTc), a brain structure implicated in sexual behaviour. The BSTc was found to be  twice as large in men and contained double the number of neurons than in women. In M2F transsexuals we found a female BSTc. The only F2M transsexual we  could study did indeed have a male BSTc.

We could exclude the possibility that the reversal of the gender difference in transsexuals was caused by changed hormone levels in adulthood. Reversal must therefore have taken place during development. When a researcher finally does publish something interesting, the nicest comment that colleagues can come up with is: “This must first be confirmed by an independent group.” That can take a while, as it took me 20 years to collect the brain material for this study.

Thus, I was delighted to hear that Ivanka Savic’s research group the Karolinska Institute in Stockholm published a study last year of functional brain scanning of living M2F transsexuals. They had not yet been surgically altered nor had they started taking hormones. They were stimulated with male and female pheromones, scents that you pick up unconsciously. These scents produce different stimulation patterns in the hypothalamus and other brain regions in control men and women. The stimulation pattern in M2F transsexuals lay between that of men and women.

Last year Ramachandran, a psychologist and  neurologist in the United States presented an interesting hypothesis and preliminary results on transsexuality. His idea is that in M2F transsexuals the representation of the penis is lacking in the cerebral cortex and in F2M transsexuals the region for breasts during development is not mapped onto the cerebral cortex, which is why the brain does not consider the organs as its “own” and wants to get rid of them.

Everything indicates that during the early stages of development, the sexual differentiation of the brain occurs atypically in transsexuals, and not that they are “simply” psychotic, as a psychiatrist from Limburg recently dared to assert.


Dit bericht heeft 8 reacties op “The atypical brain development of transsexuals”

  1. Fiona zegt:

    I must have missed something. How is this quote from the bible related to the article?

    “This is unusual because the Bible, on which the VU is founded, states in Deuteronomy 22:5-6: ‘A woman must not wear men’s clothing, nor a man wear women’s clothing, for the Lord your God detests anyone who does this.”

  2. Kim zegt:

    Dear Mr. Swaab, i really like your work but if a human being has a female brain it is a woman and not a M2F transsexual, cause she has never been male. It is very important to understand, that if the brain is teh most important sexual organ, the other organs are less important. To recognize this would help to understand that if a transsexual girl says “I am a girl” she only tells the truth. A simple truth. She never had been a boy. Thank you.

  3. Zoe zegt:

    I’m a little confused by Ramachandran’s work as presented as it’s very trivial to poke holes in it. Have they been misquoted, because no reference is provided? For a start it doesn’t explain the huge number of transfolk who never go “full-time” and thus never seek surgery or whom are non-op through choice and ignores the fact that social interaction and HRT alone go most of the way towards relieving the symptoms of gender dysphoria.

    It also seems to focus on the penis for transwomen and breasts for transmen – which are of course no the only sexual characteristics if one is obsessed by sexual parts of the body. It’s also a shame to see the usual stuff repeated, such as “Mothers describe how from the moment their son could talk, he would wear his mother’s clothes and shoes”

    All too often it seems that researches in this area are looking far too much at sex and ignoring social aspects. At least the “regretters” figure is put into context, with the percentage quoted (0.4%) rather than unnecessarily highlighting the very few out there who regret, some of whose stories do not stand up to scrutiny. (E.g. claiming to regret transition/surgery but later applying for a new birth certificate anyway)

  4. Jeffrey B. zegt:

    Very astute, Kim, and, from my perspective, right on the mark. Penis and Breast are not the determination of sexuality; sexuality, arousal, etc., etc., etc, are creatures of our brain. I am a girl, or I am a boy, is a decision housed in our minds. What is this nonsense word “Transsexual”? Let’s dump it … and fix the few physical mistakes Nature seems to have made with some of our physical body parts. By the way … I am a boy.

  5. Eldin zegt:

    Hello all,

    In regards to the ‘importance’ of breasts and penis, one must remain cautious and delineate proximate mechanisms and their product. From my reading of Dr. Swaab’s work, among transsexuals and other atypically identified individuals, there is a disjunct between their neuroprocessing circuitry and their genitalia. As other’s have put it, these individuals are generally convinced that their present genitalia simply does not match ‘them’. So, yes, in a way there is an importance on penis’. In addition to Dr. Swaab and Dr. Savics’ work, there is work conducted by Dr. Meredith Chivers (many refer to her as the “Bonobo porn lady”) that has demonstrated that genitals are indeed an important component of sexuality and sexual arousal patterns. Her research has demonstrated that whether or not men identify as heterosexual or homosexual, their sexual arousal patterns will map onto their identity. This suggests that male homosexuality (unlike female sexuality) is category specific, which means that it either conforms to a homosexual or heterosexual sexual arousal pattern.

    I end this with an important observation. To many, there seems to be something very peculiar and daunting about male homosexuality. We have tried SO hard to make claims that social and cultural factors drive or determine onset of homosexuality. However, this is simply not so. Currently, there is no evidence that postnatal social factors influence or “create” homosexuality. Many argue, myself included, that homosexuality is determined in utero- an argument for which we have a great deal of evidence. We must keep in mind that sociality and culture are only capable of exaggerating or limiting a phenotype, unless culture is able to affect gene frequencies-which, in this case it has not.

    Once we make sense of the evidence and sort it out within a evolutionary paradigm, we will able to make great strides in unlocking this fascinating puzzle.

  6. Fiona zegt:

    Hello Eldin

    I am inclined and have been so persuaded to believe people who are “born in the wrong body” are likely to have been exposed to “stress” while in the womb. Although Gunter Dorner has been given a bad wrap because of the interpretation of his work in this area, it makes a lot of sense that “homosexuality” and “transsexualism” may be induced through varying degrees and durations of “stressors” on the mother during her pregnancy. Although I could go into boring detail, a brief synopsis of Dorner’s hypothesis may at least shed a bit of light on this issue which in my belief is overly complicated on useless research on “mystery genes” and the like. Stress is an ever present part of life and is likely to be one of the hidden culprits in this line of research…

    J Homosex 1995;28(3-4):269-75
    Does peace prevent homosexuality?
    Schmidt G, Clement U
    Department of Sexual Research, University of Hamburg, Germany.
    This study attempted to replicate a series of investigations by Gunter Dorner and his associates that concluded that more homosexual men are born in wartime than in times of peace. That conclusion is based on Dorner’s belief that war induces stress in pregnant women and that stress causes a drop in fetal androgen levels which in turn leads to the development of a homosexual “orientation”. The replication not only failed to support the Dorner conclusion but also found that even those cities that suffered the most severe bombing during World War II showed no evidence of increased numbers of homosexuals. The authors conclude that homosexual men can go on loving peace and getting involved in the peace movement.
    PMID: 7560931, UI: 96028457

  7. Toby Sterling zegt:

    I agree with the first comment, by Fiona. The inclusion of the Deuteronomy quote is bizarre and has no direct connection I can see with the text.

    What does it mean to say the VU is “founded on the Bible?”

    I would love to hear an explanation, even if it’s just that the author wanted to point out there’s an additional religious debate about cross dressing.

    Additional, that is, to scientific study of transsexualism, which is what this story is otherwise about…

  8. Tycho Grouwstra zegt:

    To the above, ‘VU’ stands for ‘Vrije Universiteit’ (the university these experts were from as stated slightly earlier in the article).
    Yeah, I know, only the Dutch would get the acronym from the context.

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