Abstract
Transgender people report discomfort with their birth sex and a strong identification with the opposite sex. The current study was designed to shed further light on the question of whether the brains of transgender people resemble their birth sex or their gender identity. For this purpose, we analyzed a sample of 24 cisgender men, 24 cisgender women, and 24 transgender women before gender-affirming hormone therapy. We employed a recently developed multivariate classifier that yields a continuous probabilistic (rather than a binary) estimate for brains to be male or female. The brains of transgender women ranged between cisgender men and cisgender women (albeit still closer to cisgender men), and the differences to both cisgender men and to cisgender women were significant (p = 0.016 and p < 0.001, respectively). These findings add support to the notion that the underlying brain anatomy in transgender people is shifted away from their biological sex towards their gender identity.
Highlights
Transgender people report discomfort with their birth sex and a strong identification with the opposite sex
The observed shift away from a male-typical brain anatomy towards a female-typical one in people who identify as transgender women suggests a possible underlying neuroanatomical correlate for a female gender identity
Existing studies using multivariate classifiers aimed to assess whether the brains of transgender persons differ from their biological sex
Summary
Transgender people report discomfort with their birth sex and a strong identification with the opposite sex. Some (or perhaps all) of the aforementioned variables may have contributed to neuroanatomical variations in transgender brains, as repeatedly observed in both post mortem and in vivo studies published over the past three decades [10–28] Despite this wealth of research, a clear consensus is still missing in terms of which brain structures are altered in transgender individuals. Possible reasons include analyzing small and/or heterogeneous samples, applying different morphometric methods across studies, as well as focusing on single brain features. The latter is a concern in particular as even within cisgender studies there are large discrepancies in terms of reported sex differences, apart from the larger male and smaller female brain on average [29]. A possible solution is to study brain patterns rather than single features, as lately accomplished using modern machine learning algorithms in both cisgender samples [30–34] and transgender samples [35–38]
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