Project - Neural Correlates of Bisexuality

All Chief investigators and associate investigators

Marlon Woods, Dr. Ramon Landin-Romero

Research Project Abstract

Research on the neurobiology of sexuality is primarily composed of comparisons between heterosexual and homosexual males and females. Using multimodal brain imaging techniques, studies show significant differences in subcortical volumes, gray and white matter composition, brain network connectivity, and regional heterogeneity. To date, however, research on the neurobiology of bisexual brains is limited to one study conducted by Dr Adam Safron (currently under review). This study undertook T1 structural MRI scans of brain structure; comparing cortical thickness and grey matter volume of bisexual versus homosexual/heterosexual brains. The study failed to find significant evidence that bisexual male brains differed from homosexual or heterosexual male brains on these two structural indices and did not examine structural or functional connectivity. The current study aims to recruit 20 cisgender bisexual men and 20 cisgender bisexual women for comparison to a control sample of 80 heterosexuals (40 heterosexual men) and 60 homosexuals (30 homosexual men) collected by Professor Ivanka Savic from the Karolinska Institute, Sweden in her 2018 study of transgender brains. We will use resting state-functional Magnetic Resonance imaging (rs-fMRI) to examine structural and functional brain imaging correlates of the bisexual brain to include cortical thickness, subcortical volumes, grey matter volume, and functional connectivity.

Project tag with a disease

NA

Challenges within the field

There have and continue to be many issues with harmful assumptions about sexuality within academia as well as a stigma around the medicalization of sexuality. We are hoping to overcome these challenges and stigmas by using a co-design approach to this study to ensure the needs of the community are met.

Research Project Description

Differences in brain structure (i.e., cortical thickness, grey matter volume) and connectivity (i.e., both structural and functional) between heterosexual versus homosexual men and women have been repeatedly demonstrated (Burke, Manzouri, & Savic, 2017; Manzouri & Savic, 2018; Manzouri & Savic, 2018; Ponseti et al., 2007; Savic & Lindström, 2008). These differences are largely confined to sexually dimorphic brain regions; homosexual men show hypomasculinised brain regions relative to heterosexual men (e.g., Manzouri & Savic, 2018) and homosexual women demonstrate hypermasculinised brain regions relative to heterosexual women (e.g., Savic & Lindström, 2008).

However, whether the brains of bisexual men and women differ from those of homosexual/heterosexual men and women has not been explored – with the exception of a single study by Dr Adam Safron currently under review. This study undertook T1 structural MRI scans of brain structure; comparing cortical thickness and grey matter volume of bisexual versus homosexual/heterosexual brains. The study failed to find evidence that bisexual male brains differed from homosexual or heterosexual male brains on these two structural indices, although some structural differences were observed between bisexual and homosexual women’s brains.

Critically, however, this study did not examine structural or functional connectivity – which have recently been hypothesised to differ among bisexuals vs. monosexuals (Safron & Klimaj, 2019). This is what the present study aims to examine. Below I outline why structural and functional connectivity might hold the key to understanding the bisexual brain.

This project aims to investigate structural and functional brain imaging correlates of the bisexual brain. Specifically, we aim to examine (i) differences in white-matter tracts of bisexuals vs. homosexual/heterosexual brains, and (ii) differences in brain network flexibility of bisexual brains vs. homosexual/heterosexual brains. Finally, we aim to pool our structural data (i.e., cortical thickness and grey matter volume) with Dr Safron’s existing structural data, to examine whether structural differences in bisexual male brains emerge – when we have greater power to detect such effects. We will use a combination of multimodal neuroimaging techniques of brain structure (surface and voxel-based morphometry, diffusion tensor imaging) and function (resting state fMRI) and both whole-brain and region of interest (ROI) approaches in a relatively large sample of bisexual/heterosexual/homosexual participants.