Thursday, August 30, 2007

Sexual orientation in women - brain correlates

Ponseti et al. suggest that they can observe a brain correlate of prenatal androgenization in homosexual women - they have less grey matter in their perirhinal cortex than heterosexual women. The article starts with a useful review of the controversial literature on previously suggested brain differences between homosexual and heterosexual individuals of the same sex. Here is their abstract and two figures:
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.

Figure 1. Areas of increased GM concentration in heterosexual women compared to homosexual women. Coronal sections from y = 8 to y = −6 (p<0.05;>homosexual) was implicit masked with the contrast heterosexual (women>men). That way the intersection of significant voxels of both contrasts was gathered. As a result we found one cluster that matches both comparisons. That is, this brain area showed both, a lower GM concentration in heterosexual men compared to heterosexual women and a lower GM concentration in homosexual women relative to heterosexual women.

Figure 2. Heterosexual men and homosexual women compared to heterosexual women.
Areas of decreased GM concentration in heterosexual men are shown in blue and areas of decreased GM concentration in homosexual women are shown in yellow. Reduced GM concentration of homosexual women (relative to heterosexual women) is located within a sex dimorphic brain area.

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