Changing your sex changes your brain: influences of testosterone and estrogen on adult human brain structure

Abstract

Objective: Sex hormones are not only involved in the formation of reproductive organs, but also induce sexually-dimorphic brain development and organization. Cross-sex hormone administration to transsexuals provides a unique possibility to study the effects of sex steroids on brain morphology in young adulthood. Methods: Magnetic resonance brain images were made prior to, and during, cross-sex hormone treatment to study the influence of anti-androgenCestrogen treatment on brain morphology in eight young adult male-to-female transsexual human subjects and of androgen treatment in six femaleto-male transsexuals. Results: Compared with controls, anti-androgenCestrogen treatment decreased brain volumes of male-to-female subjects towards female proportions, while androgen treatment in female-to-male subjects increased total brain and hypothalamus volumes towards male proportions. Conclusions: The findings suggest that, throughout life, gonadal hormones remain essential for maintaining aspects of sex-specific differences in the human brain.European Journal of Endocrinology 155 S107-S114

Gender-Affirming Hormone Use in Transgender Individuals: Impact on Behavioral Health and Cognition

“…Using both cross-sectional and longitudinal design, the studies generally show that GAHT is correlated with changes in the direction of gender identity rather than natal sex with respect to global and regional brain volumes [57•, 58], white matter microstructure [59, 60], and cognitive performance on sex-biased tasks requiring verbal and visual memory [61]. To the best of our knowledge, no studies thus far have looked at how GAHT influences executive function and cognitive domains used for daily living.…”

Adult development and quality of life of transgender and gender nonconforming people

“…Studies that examined the effects of hormones on the brain (125, 126, 121) showed dramatic changes in intracranial volume, cortical thickness, volume of sub-cortical structures, and fractional anisotropy. Transgender women experienced a decrease of gray matter that produces an expansion of the ventricles, while transgender men experienced an increase of intracranial volume, cortical thickness and FA values.…”

Does having a twin brother make for a bigger brain?

“…metabolites can either prevent or induce apoptosis (38). Interestingly, in humans, in a study on cross-sex hormone administration to transsexuals, reported that androgen treatment in female-to-male subjects was capable of increasing total brain volume towards male proportions, whereas anti-androgen and estrogen treatment in male-to-female subjects decreased total brain volumes towards female proportions (39). These data support the hypothesis that in humans, the exposure to large amounts of testosterone, similar to the prenatal surge, enlarges (masculinizes) total brain volume.…”

“…The absence of effect during adulthood could also suggest that both organizational (prenatal) and activational (resulting from circulating post-pubertal levels of hormones) effects of sex steroids are important for brain volume. Thus, it may be argued that before puberty, prenatal testosterone influences brain volume (which may have behavioral effects), but when hormones are activated at puberty, they may override the prenatal effect on brain volume (12,39).…”