Abstract
Is sexual orientation associated with structural differences in the brain? To address this question, 80 homosexual and heterosexual men and women (16 homosexual men and 15 homosexual women) underwent structural MRI. We used voxel-based morphometry to test for differences in grey matter concentration associated with gender and sexual orientation. Compared with heterosexual women, homosexual women displayed less grey matter bilaterally in the temporo-basal cortex, ventral cerebellum, and left ventral premotor cortex. The relative decrease in grey matter was most prominent in the left perirhinal cortex. The left perirhinal area also showed less grey matter in heterosexual men than in heterosexual women. Thus, in homosexual women, the perirhinal cortex grey matter displayed a more male-like structural pattern. This is in accordance with previous research that revealed signs of sex-atypical prenatal androgenization in homosexual women, but not in homosexual men. The relevance of the perirhinal area for high order multimodal (olfactory and visual) object, social, and sexual processing is discussed.
Highlights
In humans, structural brain differences between men and women are well known
Two-way ANOVAs revealed higher mean tissue voxel values of males compared to females in grey matter (GM) (F1,76 = 24.8; p,0.001), white matter (WM) (F1,76 = 20; p,0.001) and cerebrospinal fluid (CSF) (F1,76 = 23.9; p,0.001)
The novel finding of the present study is that homosexual women have less GM in the temporo-basal cortex, ventral cerebellum and left ventral premotor cortex compared with heterosexual women
Summary
Structural brain differences between men and women are well known. As well as grey matter (GM) and white matter (WM) size were found to be bigger in men than in women [1,2,3,4,5,6,7]. Women have more GM volume relative to WM volume than men [8] and a higher GM concentration in widespread areas spanning the entire cortical mantle [2,3,9], as has been revealed by studies employing voxel based morphology (VBM) [10]. Gender related differences were found to be more pronounced in GM than in WM, particular if GM was calculated in normalized space, usually referred to as GM concentration. There is little consensus regarding the localization of the GM areas found to be sex-dimorphic (i.e. showing a gender related difference)
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