Testosterone Effects on the Brain in Transgender Men.

Area of Science:

• Neuroscience
• Endocrinology
• Psychiatry

Background:

• Gender dysphoria (GD) is linked to atypical brain development, but evidence is inconsistent.
• Previous research suggests GD involves disconnected self-referential and body perception networks.
• Trans men (assigned female at birth, identifying as male) offer a unique model to study hormonal effects on these networks.

Purpose of the Study:

• To investigate the impact of testosterone treatment on brain structure and function in trans men.
• To examine changes in cortical thickness, brain volumes, white matter integrity, and functional connectivity.
• To compare these changes with cisgender controls.

Main Methods:

• Longitudinal study of 22 trans men and 19 cisgender controls.
• Magnetic resonance imaging (MRI) including T1-weighted, diffusion-weighted, and resting-state scans.
• Analysis of cortical thickness, subcortical volumes, fractional anisotropy (FA), and functional connectivity before and after testosterone treatment.

Main Results:

• Pre-treatment: Medial prefrontal cortex (mPFC) was thicker in trans men than controls.
• Post-treatment: Testosterone increased insular cortex thickness and altered cortico-cortical thickness covariation between mPFC and occipital cortex.
• Testosterone also increased FA in the fronto-occipital tract and functional connectivity between mPFC and temporo-parietal junction.

Conclusions:

• Testosterone treatment induces significant structural and functional brain changes in trans men.
• These changes occur in brain regions crucial for self-referential thought and body perception.
• Findings support the role of hormonal influences in shaping neural substrates of gender identity.