The Female Brain – Part Two

Start quoting- In 2000 Kruijver published a study into BTSc neurons in 7 transsexuals and 1 gender dysphoric man. The study does not provide any evidence of a male or female brain in transsexuals. It is clear that the changes in BTSc neurons in the brain,  measured in the study, were as a direct result of transgender hormone treatment and in the case of the gender dysphoric man, likely, a statistical anomaly. There have been non transsexual individuals who have a number of BTSc neurons in their brains consistent with members of the opposite biological sex . End of quote

In 2000, Kruijver et al. published a study in which they looked at the number of neurons in the BSTc, part of the brain. They examined tissue from the same six MtF transsexuals studied by Zhou et al; one female-to-male (FtM) transsexual and from an 84-yr-old man who “had very strong cross-gender identity feelings but was never . . . sex-reassigned”.  The research says that:

1. The average BSTc neuron number in males was 71% higher than in females.

2. The six MtF transsexuals had an average BSTc neuron number in the female range.

3. The BSTc neuron number was also in the female range in the gender dysphoric male who had not received treatment for transgenderism, and was in the male range in the FtM transsexual.

This study is posted to show that :

a. The brains of FtoM transsexuals are a male one and of MtoF a female one.

b. That the existence of the one gender dysphoric male in the study, shows that sex-change hormone treatment did not cause these changes.

However in reality the study is flawed for the following reasons:

a. In 2002, research carried out by Chung, De Vries, and Swaab, showed that the differences in the number of neurons in the BSTc between females and males, did not take place until adulthood – at the earliest 22 years of age. As the majority of Transexuals report feeling that they are in the wrong body before the age of 22, these feelings appear to not be influenced by the number of neurons in the BSTc in the brain.

b. A recent study by Hulshoff Pol in 2006 showed the major effect transgender hormone therapy has on the brains of transsexuals: In eight MtF transsexuals treated for 4 months with ethinyl estradiol and CPA, total brain volume and hypothalamic volume decreased significantly with hormone therapy. It is clear that the hormones the 6 Mto F and 1 FtoM took are the most likely explanation for the finding in relation to the number of neurons in the BTSc part of the brain.

c. The one gender dysphoric male may have an atypical number of neurons in the BTSc part of his brain either because of his advanced age (84 years) or undisclosed hormone use. In any event, a single case means very little. The same study found two non-gender-dysphoric men in their control group who had BSTc neuron numbers almost identical to that of a Transsexual MtoF individual.

d. Contrary to a popular misconception, this study did not look at any nontranssexual men who had been treated with estrogen (for example, for prostate cancer) or any nontranssexual women who had been treated with testosterone. They did examine one woman, in whom an adrenal tumor had produced increased testosterone levels and one man, in whom an adrenal tumor had produced increased estradiol levels. Neither individual had BSTc volumes or neuron numbers that were unusual for their sex, but it is probable that their cross-sex hormone levels, although increased, had not been high enough and had not lasted long enough5to be equivalent to the 5-20 years of cross-sex hormone therapy that the transsexuals had received

So in conclusion, the 7 transsexuals studied had BTSc neurons in their brain consistent with the opposite biological sex, as a direct result of hormone treatment taken as part of their transitioning process. The 1 individual who is not documented as having taken hormones may have either taken them without medical knowledge, or is simply an anomaly.


Chung, W. C., De Vries, G. J., & Swaab, D. F. (2002). Sexual differentiation of the bed nucleus of the stria terminalis in humans may extend into adulthood. Journal of Neuroscience, 22, 1027-1033.

Hofman, M. A., & Swaab, D. F. (1989). The sexually dimorphic nucleus of the preoptic area in the human brain: A comparative morphometric study. Journal of Anatomy, 164, 55-72.

Hulshoff Pol, H. E., Cohen-Kettenis, P. T., Van Haren, N. E., Peper, J. S., Brans, R. G., Cahn, W., et al. (2006). Changing your sex changes your brain: Influences of testosterone and estrogen on adult human brain structure. European Journal of Endocrinology, 155(Suppl. 1), S107-S114.

Kruijver, F. P., Zhou, J. N., Pool, C. W., Hofman, M. A., Gooren, L. J., & Swaab, D. F. (2000). Male-to-female transsexuals have female neuron numbers in a limbic nucleus. Journal of Clinical Endocrinology and Metabolism, 85, 2034-2041.

Zhou, J. N., Hofman, M. A., Gooren, L. J., & Swaab, D. F. (1995). A sex difference in the human brain and its relation to transsexuality. Nature, 378, 68-70.

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