Grant: Canada Postdoctoral Research Award (CPRA) program

About 1% of Canadian adolescents are transgender, with transgender boys (TB; boys with ovarian health considerations) comprising 80% of youth seeking gender care, including gender-affirming hormone therapy (GAHT). Yet, research on its neurocognitive impacts has neglected treatment aspects unique to TB, such as GAHT-induced suppression of ovarian cycling. Ovarian suppression is, nevertheless, associated with neurocognitive masculinization in women's health contexts, as well as memory decline-both of which are outcomes of transmasculine GAHT (i.e., testosterone provision). It is thus unclear whether GAHT's impacts on transmasculine brain health and development stem from androgen supplementation or ovarian suppression. To disentangle these, I will first characterize brain structure and function of treatment-naïve TB, and sex- and gender-matched peers-expecting some aspects to align with gender, not sex. I will then map brain change post-GAHT, expecting further alignment with gender, and changes in ovarian-dependent function. To isolate effects of ovarian suppression, I will also map brain change between timepoints, during puberty-blocking (PB) treatment-capturing structural and functional alterations that predate testosterone provision. At follow-up timepoints, PB- and GAHT-treated TB will be compared to cisgender peers and treatment-naïve TB, providing a sex- and gender-matched developmental baseline. Neuroimaging data will be combined with hormone and psychometric data, and examined across regions-spotlighting not just hormone-sensitive areas that underpin sex-typed cognition (e.g., visuospatial circuits) but also everyday cognition and brain health (e.g., memory circuits). GAHT's impacts on the developing brain have yet to be studied longitudinally, or through an ovarian lens, placing a disproportionate burden on transmasculine youth's health. The proposed research will fill this knowledge gap, inform treatment decisions, and facilitate inclusive gender care.