Research Article: Sexual Orientation Related Differences in Cortical Thickness in Male Individuals

Date Published: December 5, 2014

Publisher: Public Library of Science

Author(s): Christoph Abé, Emilia Johansson, Elin Allzén, Ivanka Savic, Antonella Gasbarri.


Previous neuroimaging studies demonstrated sex and also sexual orientation related structural and functional differences in the human brain. Genetic information and effects of sex hormones are assumed to contribute to the male/female differentiation of the brain, and similar effects could play a role in processes influencing human’s sexual orientation. However, questions about the origin and development of a person’s sexual orientation remain unanswered, and research on sexual orientation related neurobiological characteristics is still very limited. To contribute to a better understanding of the neurobiology of sexual orientation, we used magnetic resonance imaging (MRI) in order to compare regional cortical thickness (Cth) and subcortical volumes of homosexual men (hoM), heterosexual men (heM) and heterosexual women (heW). hoM (and heW) had thinner cortices primarily in visual areas and smaller thalamus volumes than heM, in which hoM and heW did not differ. Our results support previous studies, which suggest cerebral differences between hoM and heM in regions, where sex differences have been reported, which are frequently proposed to underlie biological mechanisms. Thus, our results contribute to a better understanding of the neurobiology of sexual orientation.

Partial Text

The origin and development of a person’s sexual orientation, and the feeling of being sexually attracted to a person of opposite, same or both sexes, is still a controversial topic. Research pointing to the fact that neurobiological processes are involved in the development of an individual’s sexual orientation is emerging. Among the contributing factors it has been suggested that mechanism similar to those influencing the female/male differentiation (sexual dimorphism) of the human brain during the fetal, neonatal and pubertal development could be involved. Such mechanisms include genetic information and/or effects of sex hormones. For example, sexual dimorphism of the brain, as well as sexual orientation has been linked to effects of testosterone, see [1]–[10] and references therein. While the literature on sex differences in the human brain is extensive, research on neurobiological characteristics of sexual orientation in humans is very limited.

To contribute to a better understanding of the neurobiology of sexual orientation, we investigated possible differences in regional cortical thickness (Cth) between heterosexual men (heM) and homosexual men (hoM). The group comparisons included heterosexual women (heW) in order to explore, whether (and if so, which of) the differences observed were present in regions, which indicate sex related differences.