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Wednesday, June 18, 2008

The Neurobiology of Sexual Orientation

According to a new study, sexual orientation may be linked to the symmetry of your brain. Ivanka Savic and Per Lindström, researchers at the department of clinical neuroscience at the Stockholm Brain Institute in Sweden, have brain scans that show that the brains of heterosexual men and homosexual women—in other words, people who are sexually attracted to women—have right hemispheres larger than the left. Heterosexual women and homosexual men, on the other hand, both have symmetrical brains. The study, published this week in the Proceedings of the National Academy of Sciences online, is bolstering the idea that biological factors influence sexual orientation and expanding the idea of which brain regions might make a difference.
MRI and PET scans of 90 people, seen in the above image from PNAS, also showed similarities between straight men and gay women and similarities between straight women and gay men in the wiring of the amygdala, a region of the brain that's key for processing emotions and the fight-or-flight response. "The observations cannot be easily attributed to perception or behavior," the researchers write. "Whether they may relate to processes laid down during the fetal or postnatal development is an open question." —Heather Wax


Julia C. Keller said...

Sexual preference and neurobiology isn’t new territory for Ivanka Savic. At Stockholm's Karolinska Institut, Savic’s group has been investigating brain responses to pheromone-like smells in relation to sexual orientation and sexual reassignment. Straight men and lesbians liked the female pheromone more than the male one. Men and lesbians also found the male hormone more irritating than the female one, while straight women were more likely to be irritated by the female hormone than the male one. Savic hasn’t crossed the boundaries of researcher into pundit, but she does say that the evidence is hard to dispute. “The findings of the study show that it is difficult to interpret homosexuality as a learned behavior”, Ivanka Savic said in an interview with the Swedish newspaper Dagens Nyheter.

Though all these scientific studies of sexual orientation help bolster the case for nature not nurture, the general public might start to wonder why we are spending the money to measure the length of folks’ ring fingers compared to their pointer fingers (2D:4D) or to determine whether left-handed men with several older brothers (handedness, fraternal birth order) and hair that swirls counter-clockwise (hair whorl pattern) are sure to be gay. Quick! Go check in the mirror and take a look at your hands! You too might be gay!