Sex. It happens in your brain

Sex. It happens in your brain. That’s what Dear Abby, Ann Landers and Dr. Ruth all used to say. They were on to something.

Hello, my name is Jude, aka geekgirl on jaysays.com. I’m straight and I’m a molecular biologist. I’m fascinated by all things biological, especially the human brain. I would like to introduce you to just one of many research articles addressing the question of sexual orientation. I was delighted to see Truth and Love devote a week to gathering real facts on this very important topic. Are gay people born this way? More and more hard evidence is accumulating that points in this direction. Science has moved beyond asking people what they feel.

Researchers in Sweden studied the symmetry and connectivity of the brains of straight men, straight women, gay men and lesbians. This work was published in April 2008 in the very prestigious journal Proceedings of the National Academy of Science.

The original reference is: PET and MRI show differences in cerebral asymmetry and functional connectivity between homo- and heterosexual subjects. Authors Ivanka Savic* and Per Lindstro¨m Stockholm Brain Institute, Department of Clinical Neuroscience, Karolinska Institute, 171 76 Stockholm, Sweden. PNAS April 2008.

The study itself is highly technical and not easy reading for us every day folks without this level of training. However, it can be translated into terms we can all understand. The researchers asked two main questions. Are the two halves of the brain symmetrical or asymmetrical? Are there differences in functional connectivity between the two halves of the brain? In the words of the authors, “

The choice to measure amygdala connectivity was based on several reports about sex differentiated amygdala lateralization in processing of emotional memories (with an activation of the right amygdala in men, and the left amygdala in women and potential neurobiological correlates to sex and sexual orientation. In addition, the amygdala is a key structure in the limbic networks and exhibits high density of estrogen and androgen receptors.”

The study used ninety subjects. 25 heterosexual men, 25 heterosexual women, 20 homosexual men and 20 homosexual women. The difference in the number of subjects is not statistically significant. The brains were analyzed using PET measurements of blood flow to measure functional connections between the two halves of the brain.

In this case, a picture is able to replace a lot of words. Take a look at the photo and compare the brains. See the red and yellow areas? In the left amygdale, the heterosexual male brain looks very similar to the homosexual female brain. And the heterosexual female brain looks very similar to the homosexual male brain. The right amygdale does not show this clear cut pattern but it is clear that there is a difference between heterosexual and homosexual men.

If we were using photos of our brains to tell us gender, instead of our genitalia, who would you call a boy or a girl? The researchers also looked at the volume of each half of the brain using MRI. The paper shows the variation in the data and the statistics proving the differences.

For the sake of simplicity, I’ll just include the result. Left Half HeM 25 624 612 These are significantly different. HeW 25 581 581 These are not significantly different. HoM 20 608 609 These are not significantly different. HoW 20 548 543 These are significantly different.

The authors concluded that “The present study shows sex-atypical cerebral asymmetry and functional connections in homosexual subjects.

The results cannot be primarily ascribed to learned effects, and they suggest a linkage to neurobiological entities.” Now, does this study prove that these differences are the cause of sexual orientation? One study alone doesn’t do that. But it is very clear that the brains of straight people and gay people are different. Not only different, but straight men and lesbians share similarities and straight women and gay men share similarities.