Interesting Research on FTM Adolescents
In 2022, a team working with Kenneth Zucker conducted research on the brains of gender dysphoric teenage girls. The team did not find evidence of cross-sex brain features in this group, where most participants reported non-gynephilic attractions. Instead, the team found differences in “brain areas implicated in own-body perception and self-referential thinking.”
At a glance, this seems to be consistent with studies on FTM adults. Their findings differ from a study conducted by Nota et al., which found male-like brain features in dysphoric teenagers who exclusively reported gynephilic attraction. However, these teenagers were also administered GnRHas (“puberty blockers”). It is therefore possible that brains only appeared similar to male controls as a side-effect of pubertal suppression. Notably, Kenneth Zucker’s team found patterns that “did not support the prediction that the brain functional connectivity patterns of gynephilic GD AFAB should reflect those of gynephilic cisgender boys.”
It is possible that I have been mistaken about the brain research on FTMs. Another factor to consider is a shortcoming of research on FTMs, where researchers rely on self-reported sexual orientation. In a post queer theory world, the concept of “gynephilia” is destroyed. It is common for adolescent girls to describe their sexuality as “lesbian”, when they are attracted to anything ranging from a “gynandromorph” to a fully intact male that self-identifies as female. It is especially common for gender dysphoric adolescents to be confused about their sexuality. Is it possible that the teenagers who reported gynephilic attraction were actually bisexual, or androphilic? Could this be why Zucker’s team failed to find male-like brain patterns?
In the future, instruments for the objective measurement of sexual orientation are vital for the research of FTM transsexuality.
EDIT: As it turns out, this research team did find some evidence of cross-sex brain features in gynephilic, gender dysphoric, female adolescents.
Skorska et al. (2021) studied three features of cortical gray matter structure and microstructure in 76 brain regions: surface area, cortical thickness, and T1 relaxation time. They found that "gynephilia, older age, and stronger attractions (in cisgender boys only) were related predominantly to shorter T1 in regions distributed throughout the frontal, temporal, parietal, and occipital lobs. Thus, in GD AFAB [gender dysphoric female adolescents] and cisgender boys, brain patterns showed similarities in how they varied in relation to sexual orientation as well as developmentally (i.e., in relation to age)."
Several follow-up studies were conducted on largely overlapping cohorts.
Skorska et al. (2022) analyzed inter-network brain functional connectivity. As mentioned previously, they did not find evidence of cross-sex brain features, even in the gynephilic adolescents.
Skorska et al. (2023) studied mean diffusivity and T1 relaxation time, finding that, "in several left frontal, parietal, and temporal regions, the combination of shorter T1 relaxation time and faster MD was associated with older age and greater gynephilia in GD AFAB [gender dysphoric female adolescent] individuals and cisgender boys and with stronger attractions in cisgender boys only. Thus, for these cortical regions in these groups, older age, gynephilia, and stronger attractions (cisgender boys only) were associated with macromolecule-rich tissue in which water movement was freer—a pattern that some prior research suggests is associated with greater cell density and size."
Thurston et al. (2024) investigated white matter microstructure using diffusion tensor indices (fractional anisotropy; mean, radial, and axial diffusivity (AD)) and quantitative T1 relaxometry (T1). They describe the following relationship between AD and sexual orientation:
"Direction of sexual attraction correlated with AD negatively in cisgender and transgender boys, and positively in cisgender girls. The majority of cisgender boys reported some degree of gynephilic attraction, whereas a range of gynephilic and androphilic attractions were reported by transgender boys. The findings potentially suggest that the combination of gynephilic sexual attraction and a masculine gender identity are associated with more axonal packing or density. Gynephilic attraction was also related to shorter T1 in cisgender boys, indicating more myelination. These WM findings could extend to previous gray matter morphometric/structural findings from a largely overlapping cohort [39]. It was found that greater gynephilic attractions were related to shorter T1 in several cortical regions across the brain in cisgender and transgender boys [39]. Together, the studies potentially describe a neural phenotype for gynephilia in masculine-identifying individuals."
"AD was positively correlated with direction of sexual attraction in cisgender girls, who mostly reported some degree of androphilic attraction. This relationship opposes the negative correlation in cisgender and transgender boys and may suggest that greater axonal density is associated with a higher degree of androphilia specifically in feminine-identifying individuals. Although these inferences would benefit from the inclusion of more sexual diversity (e.g., another feminine gender group) [i.e., gender dysphoric male adolescents], the relationships do demonstrate that sexual attraction metrics should be considered in future WM microstructure research."
Further research would benefit from including a larger sample of gynephilic cisgender girls, to determine whether they have identified a unique neural phenotype for "gynephilia in masculine-identifying individuals" or simply "gynephilia".
From Skorska et al. (2023):
"Future research could also address some of the present study’s limitations. We had relatively small sample sizes. In addition, representation across sexual attractions and gender identity could be improved. The cisgender boys and girls examined here were disproportionately gynephilic and androphilic, respectively, and the study lacked a group of individuals assigned male at birth who experienced gender dysphoria. The lack of such participants limits the conclusions that can be drawn. For example, given the lack of cisgender gynephilic girls, it is unclear whether gynephilia is associated with a cortical pattern of slower T1 and faster MD regardless of whether one’s gender expression is masculine or feminine. The study also lacked a comparison of transgender youth who identified with a binary gender (i.e., girl or boy) to those with a nonbinary gender identity. In addition, our sample was limited to adolescents. Given that our findings suggest cortical gray matter density in masculine gynephilic individuals covaries with increased age over adolescence, this pattern of psychosexual-related neural characteristics might be more evident in adult samples."
References
Skorska, M. N., Chavez, S., Devenyi, G. A., Patel, R., Thurston, L. T., Lai, M.-C., Zucker, K. J., Chakravarty, M. M., Lobaugh, N. J., & VanderLaan, D. P. (2021). A Multi-Modal MRI Analysis of Cortical Structure in Relation to Gender Dysphoria, Sexual Orientation, and Age in Adolescents. Journal of Clinical Medicine, 10(2), 345. https://doi.org/10.3390/jcm10020345
Skorska, M. N., Lobaugh, N. J., Lombardo, M. V., van Bruggen, N., Chavez, S., Thurston, L. T., ... & VanderLaan, D. P. (2022). Inter-network brain functional connectivity in adolescents assigned female at birth who experience gender dysphoria. Frontiers in Endocrinology, 13, 903058.
Thurston LT, Skorska MN, Lobaugh NJ, Zucker KJ, Chakravarty MM, et al. (2024) White matter microstructure in transmasculine and cisgender adolescents: A multiparametric and multivariate study. PLOS ONE 19(3): e0300139. https://doi.org/10.1371/journal.pone.0300139
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