Hello. Aren't most studies just "proving" transgender brains are "resembling" the "desired sex" as an effect of hormones? If so it is not a innate characteristic, or are there studies that focus on pre-hormone transgenders and how reliant and representative are they?
Most of the research I focus on is on pre-HRT trans people, specifically for the reason that sceptics can easily find reasons to disregard significant neurological findings as a product of HRT if it’s a confounding factor. Rest assured, there is plenty of evidence that pre-transition trans people have unique neurology that separates them from cis people, there is evidence of such differences present from childhood, and most are thought to be connected to innate biological factors.
Transgenderism is, technically, an effect of hormones -- but pre-natal hormone exposure, not HRT. The most-cited theory (and the one that makes the most sense) suggests that abnormal levels of pre-natal hormones are responsible for the structural and functional differences we see in trans people’s brains and are a determining factor in their gender identity, making it an innate neurobiological feature. Besides the research being done on trans brains, there is also research on the gender identities of intersex people with hormone-related DSDs, and non-neurological research on trans people implicating hormone-related polymorphisms, that support this explanation.
As far as transgender brains “resembling their desired sex” goes, I’ve already addressed that in a couple other answers so I’m just going to link them to avoid repeating myself [1] [2]. TLDR, any claims of trans people having the brain of their desired sex is an oversimplification of and disservice to the research that just invites unnecessary scepticism. When making broad statements about the whole brain, it’s far more accurate and helpful to explain that trans people’s brains are atypical for their birth sex, not that they are completely sex-reversed.
My scholarly sources spreadsheet has a ton of studies on pre-HRT trans people and comparing pre-HRT with hormone-treated trans people, if you want to peruse. Just a few that I know meet that criteria:
Biological origins of sexual orientation and gender identity: Impact on health (O’Hanlan, et al., 2018) [full text] - Review article summarizing relevant research for doctors outside of the field. Covers several ways pre-treatment trans people have shown to differ from cis controls. Surface-level but very accessible read.
Male-to-Female Transsexuals Have Female Neuron Numbers in a Limbic Nucleus (Kruijver, et al. 2000) [open access] - Outdated now, but significant as some of the first research demonstrating sex-atypical traits in trans people’s brains. Finds that hormone use is not a factor to the differences described.
White Matter Microstructure in Transsexuals and Controls Investigated by Diffusion Tensor Imaging (Kranz, et al., 2014) [open access] - Controls for individual estradiol, testosterone, & progesterone levels and excludes participants who have received hormone treatment. Finds that trans people occupy a middle ground between cis male & female controls. Similar scope & results to this pair of studies from 2011 [1] [2].
Neuroimaging Differences in Spatial Cognition Between Men and Male-To-Female Transsexuals Before and During Hormone Therapy (Schöning, et al. 2010) [full text] - Tests both pre- & post-HRT trans women. Finds functional differences from cis male controls in both groups.
Structural connections in the brain in relation to gender identity and sexual orientation (Burke, et al., 2017) [open access] - Controls for sexual orientation and excludes participants who have received hormone treatment. Finds that the area of the brain mediating self-perception is sex-atypical in trans people.
Brain structure and function in gender dysphoria (Bakker, 2018) [abstract only] - Participants are all pre-puberty. Preliminary findings show grey matter volumes are sex-atypical in gender dysphoric children.
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