Karissa speaks with a trauma therapist named Katie who has both professional and personal experience around the topic of transgender. Her unique position as both a clinician and a mother of a transgender child provides both personal and informed perspective to the topic. We discuss Katie's personal and professional connection to the subject, the biological nature of the transgender brain, and dispel common narratives and misinformation on the subject.

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Cortical Thickness and Gray Matter Volume

• Luders et al. (2009) "Regional gray matter variation in male-to-female transsexualism": This study used voxel-based morphometry (VBM) to analyze gray matter volumes in untreated transgender women. It found that while overall gray matter was closer to the male pattern, transgender women had a significantly larger gray matter volume in the right putamen compared to cisgender men, a finding that deviated from the typical male/female patterns and was considered a unique finding.
• Zubiaurre-Elorza et al. (2013) "Cortical thickness in untreated transsexuals": This study found that in specific regions (insular, orbitofrontal, and medial occipital regions), the cortical thickness of untreated transgender women was more similar to that of cisgender women than cisgender men, suggesting a "feminization" in those specific areas.
• Simon et al. (2013) (referenced within other articles): This study found that cisgender women and transgender women had a smaller gray matter volume in their left somatosensory and primary motor cortices in comparison to cisgender male controls, suggesting a female-typical pattern in these regions.

White Matter Microstructure

• Rametti et al. (2010) "The microstructure of white matter in male to female transsexuals before cross-sex hormonal treatment": This diffusion tensor imaging (DTI) study found that the white matter microstructure patterns in untreated transgender women were often intermediate between those of cisgender male and female controls, not fully matching either, but showing an "incomplete masculinization" compared to cisgender men in tracts like the superior longitudinal fasciculus and forceps minor.

Hypothalamic and Subcortical Structures (Post-mortem studies)

• Zhou et al. (1995) "A sex difference in the human brain and its relation to transsexuality": This pioneering post-mortem study found that the volume of the central part of the bed nucleus of the stria terminalis (BSTc) in transgender women was similar in size to that of cisgender women and significantly smaller than in cisgender men.
• Kruijver et al. (2000) "Sex hormone studies in the postmortem human brain": This study supported the 1995 findings, showing that the neuron number in the BSTc of transgender women was also feminized (similar to cisgender women).
• Garcia-Falgueras and Swaab (2008) "Sex differences in the human brain, transsexuality, and intersexuality": This research group found that another interstitial nucleus of the anterior hypothalamus (INAH3) in transgender women was also similar in volume and neuron number to that of cisgender women.

Large-Scale Mega-Analyses

• Mueller et al. (2021) "The Neuroanatomy of Transgender Identity: Mega-Analytic Findings From the ENIGMA Transgender Persons Working Group": This large-scale study, which combined data from multiple sites, found that rather than simply shifting toward the female pattern, transgender people "seem to present with their own unique brain phenotype". They found differences in subcortical volumes and surface area compared to cisgender controls, with patterns varying by region and measure.

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