Do Ancient Brain Regions Help Define Our Sexual Orientation?

Lawmakers in Florida and Texas have supported a bill that bans discussions of sexual orientation in schools. Their concern is that discussing gay lifestyles or gay people might alter a person's sexual orientation. Is this possible? Can hearing a discussion alter the structure of brain regions responsible for sexual orientation? To answer this question, it is critical to understand how the brain might express sexual orientation.

Decades of investigations have confirmed that several brain regions are anatomically different in males and females. The precise brain anatomical correlates that most reliably and specifically indicate a person’s sexual orientation has been the subject of several recent correlational studies. Interestingly, these studies have linked sexual orientation to anatomical differences in phylogenetically ancient regions of the brain that were not identified in earlier studies, particularly the putamen and thalamus. The putamen is involved in the cognitive processes that create one’s own body image.

Here’s a summary of what has been reported recently.

1. Heterosexuals have a bigger thalamus and motor cortex, while homosexuals, particularly homosexual women, have a bigger putamen than heterosexual individuals.
2. Transwomen, i.e., women who were assigned male at birth, have an enlarged putamen.
3. In contrast, transmen, i.e., men who were assigned female at birth, have a smaller putamen.
4. Heterosexual females had a higher volume of grey matter in their thalamus and caudate nucleus [a brain region near the putamen] as compared to homosexual females.
5. Heterosexual males have a larger putamen than homosexual males.
6. The anterior hypothalamus was smaller in homosexual men than in heterosexual men but was similar in size to the same region in heterosexual women.
7. Finally, imaging studies reported sexual orientation‐related differences in cortical regions devoted to vision. Gender identity may influence how we see the world, literally.

Overall, specific brain regions in homosexual males tended to be similar to those in heterosexual women (more female‐typical), while these same brain regions in homosexual women tended to be similar to those in heterosexual men (more male‐typical). Furthermore, the brain regions of interest became larger in homosexual females and smaller in homosexual males, as compared with their heterosexual counterparts.

In Summary:

The anatomical differences in some of the brain’s most ancient regions are a consequence of the interaction of complex hormonal and genetic influences during brain development. The changes described in these publications are correlational and do not prove that sexual orientation is determined by brain anatomy. Future studies will be needed to unravel the complex interaction of genetic and environmental factors that influence sexual orientation.