The science of gender and sex is both complex and also built upon ever-shifting epistemological and ontological foundations. Binary Brain-Sex activists claim that Zhou, Hofman, Gooren, & Swaab(1995) has proven that MTF Transsexuals have a “Woman’s Brain Sex”. However, social construction, Psychodynamic theories of desire, and Neuroanatomy are all intertwined in the creation of Gender. I am re-publishing a recent review of the scientific literature in order to show you just how messy the bleeding-edge science is before it is reduced to cyberwar soundbites. This is tough reading but when you are done you are an “Brain Science Expert.”
I am extremely pleased that this paper examines all of the Gender Variance spectra which includes Third Genders, Male-Genderqueers, Male Lesbians, Autogynephiles and Drag Queens. This paper should be the non-reductionist standard for terminology. Even the term Transgender is politically loaded by claiming to speak for all gender variants.
Biological and psychosocial correlates of adult gender-variant identities
by Jaimie F. Veale, David E. Clarke, Terri C. Lomax
2.3. Neuroanatomical correlates
One research team has found a sex differentiation in the neuron volume of the central subdivision of the bed nucleus of the stria terminalis (BSTc) of the hypothalamus and in postmortem examinations of transsexuals’ brains found that their BSTc neuron volume matched that of their opposite birth-assigned sex (Kruijver et al., 2000; Zhou, Hofman, Gooren, & Swaab, 1995). Their sample included six MF transsexuals and one FM transsexual who had received hormone treatment for a significant period of time. These MF transsexuals were all non-androphilic (Garcia-Falgueras & Swaab, 2008). Kruijver et al. also included a male who ‘‘had very strong cross-gender identity feelings” (p. 2039) but never received hormone treatment in their sample and found a BSTc neuron volume within the female range for this person. Both studies also included six ‘‘sex hormone disorder” cases that had atypical hormone levels but NGV, and came to the conclusion that the BSTc differences were not associated with hormone treatment in either the transsexuals or NGVs. Given their findings, Zhou et al. and Kruijver et al. proposed a neurobiological basis as an explanation of transsexualism.
More recent research has discovered that sex differences in BSTc volume do not develop until well into adulthood (Chung, De Vries, & Swaab, 2002) and yet the majority of transsexuals report that their transsexual feelings began before adulthood (Veale, Clarke, & Lomax, submitted for publication-c). Lawrence (2007, details from the author) also argued that there is insufficient evidence that these brain differences were not the effect of hormone treatment, given studies finding hormone treatment for MF transsexuals decreased overall brain volume, and in FM transsexuals both hypothalamic and overall brain volume increased with hormone treatment (Hulshoff Pol et al., 2006). A study has also found that pedophilic offenders also have a smaller BST size than non-pedophilic males (Schiltz et al., 2007). Finally, there is also evidence from experimental studies of animals and correlational studies of humans that childhood stress (including abuse) has an impact on brain structure, including the hypothalamus (Kaufman, Plotsky, Nemeroff, & Charney, 2000; Teicher, Tomoda, & Andersen, 2006). Clearly, further independent research using larger samples is needed to assess the BSTc as a proposed neurobiological basis as an explanation of transsexualism.
The interstitial nucleus of the anterior hypothalamus nuclei 3 (INAH-3) has previously been shown to be sexually dimorphic and it has been reported that NGV homosexual males also have a female-typical INAH-3 size (Byne et al., 2001; LeVay, 1991). Garcia-Falgueras and Swaab (2008) found 11 MF transsexuals had an INAH-3 that was a smaller, female-typical size. The group differed from 14 NGV males but not from 11 NGV females. They also reported the INAH-3 size of one FM transsexual was within the male range. Given that most of the MF transsexuals in this research were non-androphilic this finding has interesting implications for the relationship between sexual orientation and gender identity. Garcia-Falgueras and Swaab found that INAH-3 size of five castrated males was intermediary between male and female NGVs, suggesting that androgen level changes in adulthood may have an effect on INAH-3 size.
Other research has found that 22 MF and 28 FM transsexuals have corpus collosum midsaggital plane shapes (measured using MRI scans) more typical of those of the gender they identify as, when compared to NGVs (Yokota, Kawamura, & Kameya, 2005). A recent study has found that non-androphilic MF transsexuals who had not been taking cross-sex hormones showed a femaletypical hypothalamus activation pattern when smelling odorous steroids known to activate the hypothalamus (Berglund, Lindstrom, Dhejne-Helmy, & Savic, 2009). Another study found that 6 androphilic and 18 gynephilic MF transsexuals who had not commenced hormone therapy had gray matter variation that was more similar to NGV males than NGV females, although transsexuals of both sexual orientations had a female-typical volume of grey matter in the left putamen (Luders et al., 2009).
Underlying differences in neuroanatomic structure can also be manifested in cognitive test performance. Studies of cognitive abilities of persons with gender-variant identities are outlined in Table 6. Almost all of this research has been conducted on transsexuals. Overall, these results are mixed, with some studies showing no differences between transsexuals and NGVs of the same birth-assigned sex and some showing transsexuals’ cognitive test performance in line with their gender identity. It also appears that transsexuals’ hormone treatment does not have much effect on the results (e.g. Haraldsen, Egeland, Haug, Finset, & Opjordsmoen, 2005). The most likely reason for these mixed findings is the small sample sizes of both transsexuals and NGVs in most of the studies. It is also possible that studies that included more transsexuals who were sexually attracted to the same birth-assigned sex (Collaer, Reimers, & Manning, 2007; Peters, Manning, & Reimers, 2007) were more likely to report between-group difference because this sexual orientation has been associated with sex-atypical results on these cognitive tests among NGVs.