More Parts of the Puzzle

CNN is now reporting on the same kind of research on opposite-sex twins that I mentioned in BiGender and the Brain.

And the latest issue of Cerebral Cortex has an article, Male-to-female transsexuals show sex-atypical hypothalamus activation when smelling odorous steroids. by Berglund H, Lindström P, Dhejne-Helmy C, and Savic I.

As per usual, lesbian MtoF women are described as "nonhomosexual". One day, the penny will drop.

From the article itself (rather than the online abstract) :

Transsexuals have the strong feeling, often from childhood onward, of having been born the wrong sex. The possible etiology of transsexualism has been the subject of debate for many years (Benjamin 1967; van Goozen et al. 2002; Swaab 2004; Gooren 2006). Investigation of the genetics, hormone levels, gonads, and genitalia of transsexuals has not produced results that explain their status (van Goozen et al. 2002; Swaab 2004; Gooren 2006). In experimental animals, the gonadal hormones that prenatally determine the morphology of the genitalia are shown to also influence the morphology and function of the brain in a sexually dimorphic manner (Fels and Bosch 1971; Yalom et al. 1973; Baum 2003 2006). This led to the hypothesis that sexual differentiation of the brain in transsexuals might not have followed the line of sexual differentiation of the body as a whole and that transsexual persons may have sex-atypical cerebral programing (van Goozen et al. 2002). Such a scenario can be evaluated in humans by comparing transsexual and control subjects with respect to sexually differentiated cerebral functions.
...
In the quest for reliable in vivo methods to study sex differences in the neurobiology of the hypothalamus, we designed positron emission tomography (PET) activation experiments measuring changes in regional cerebral blood flow (rCBF) during smelling of 2 steroidal compounds: the progesterone derivative 4,16-androstadien-3-one (AND) and the estrogen-like compound estra-1,3,5(10),16-tetraen-3-ol (EST) (Savic et al. 2001, 2005; Berglund et al. 2006). AND is present in human male secretions such as sweat, saliva, and semen (Grosser et al. 2000), whereas EST has been detected in the urine of pregnant women (Thysen et al. 1968).
...
Several centers currently recognize essentially 2 types of MFTRs who can be distinguished on the basis of their sexual orientation (Chivers and Bailey 2000; Smith et al. 2005). The first type is homosexual transsexuals, extremely gender-transposed (feminine) men, whose sexual object choice is toward men instead of women. The second type is men, whose sexual object choice is interpreted to be toward the image of themselves as women. For this group, the primary motivation for changing sex is to become the object of their own desire (Chivers and Bailey 2000; Smith et al. 2005). In this respect, all our patients can be regarded as nonhomosexual (gynaecophyl) transsexuals (Chivers and Bailey 2000), although we used a more operative approach in our classification, taking into consideration also the sexual partners, sexual fantasies, and expressed attractions (Kinsey 1953Go).

They have a very diplomatic way of saying that Civers and Bailey are full of it. Because "men, whose sexual object choice is interpreted to be toward the image of themselves as women" would hardly have female anatomy, would they? If they did, then how could we classify them as "men", except arbitrarily? And the studies show pretty conclusively that they do have at least feminised anatomy, when it comes to parts of the brain.

The generated data relate to reports by Swaab's group of a female size of BNSTc in MFTRs (Zhou et al. 1995Go; Kruijver et al. 2000Go). Although structural and functional dimorphism are not directly translatable and the BNST is too small to be detected with the imaging methods applied, it is of note that this nucleus in animals mediates pheromone signaling and that it in humans has reciprocal connections with the anterior hypothalamus (Eiden et al. 1985Go). Both Swaab's and our findings may, therefore, reflect a common organizational deviation of certain sexually dimorphic circuits involved in human reproduction. Whether and how this links to the perception of sexual identity remains unclear and awaits further investigations.

I would have said "gender identity and sexual orientation", two separate concepts, but no matter.

In summary, albeit the present study does not provide conclusions concerning the possible etiology, it suggests that in transsexuals the organization of certain sexually dimorphic circuits of the anterior hypothalamus could be sex atypical. It adds a new dimension to our previous reports by showing that the observed effects are not necessarily learned and that a sex-atypical activation by the 2 putative pheromones may reflect neuronal reorganization.

Having had a look at the study, they went to extraordinary lengths to shackle all the variables. They even insisted on only right-handed subjects being included. All in all, extremely good Science.

At some stage... eventually... the American Psychiatric Association and others are going to realise that they can't continue to ignore the neurological data in favour of psychiatric conjectures.

And finally, for my own reference as much as anything else, their list of articles:

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