Guess what? Gays and lesbians and straights and the rest . . . they’re different! Who woulda thunk it?

A new study indicates that lesbians’ brains may respond differently . . . study offers clues to sex orientation. The study looked specifically at how the brain processes aroma, particularly human sex pheromones. The researchers found that lesbians process the pheromones differently than straight women, straight men, or gay men. Of particular interest is the following . . .

She said it was significant that lesbian brain responses weren’t just a female version of male heterosexuality, and nor were lesbian brains just a mirror image of the gay male brain. “Sexual orientation may well have a different basis in women than in men,” Witelson said. “It’s not as simple as gay men being more like women, and lesbians being more like men. There are two sexes, which we know are biologically different in some respects, and variation in sexual behavior within each sex is not necessarily the same as in the other sex.”

That’s a big deal as it indicates that sexual orientation works differently for lesbians than it does for gay men and that orientation may be far more complex than the simple mirroring effect previously believed.

Lesbians seem to have different brain circuitry than heterosexual women, processing the aroma of sex hormones in a way more similar in some respects to the brain response of straight men, a new study has found. A team of neuroscientists in Sweden already has reported evidence suggesting that the brains of men and women, as well as the brains of gay men and straight men, handle male and female hormone smells in distinct ways. On Monday, the same researchers, led by Ivanka Savic of the Stockholm Brain Institute and Hans Berglund of the Karolinska University Hospital, reported similar differences in women. Results appear in the latest Proceedings of the National Academy of Sciences. Twelve women identified as strongly homosexual were subjected to brain scans while the scientists presented an array of aromas, in particular a sample of male and female sex hormones. A group of women identified as straight were also presented the aromas. The results showed that while a part of the brain called the anterior hypothalamus — which is linked to sexual behavior, among other things — tended to light up in the straight women, the lesbians showed no reaction. On the other hand, lesbians tended to react to male as well as female hormones in the part of the brain that handles routine odors. Many important aspects of sex-hormone processing in the brain haven’t been worked out, but the researchers concluded that the lesbian women clearly handled hormone smells differently than heterosexual women, and in a way that seems to be “in partial congruence” with heterosexual men. Along with the previous results, the new study suggests that sexual preferences are linked to brain function in ways scientists are just beginning to understand. But it’s unclear how these brain differences arise, or whether they are more a cause or a consequence of behavior. “Something is happening but we don’t know if it’s learning, and we don’t know if its biological — we don’t know anything about that,” said Charles Wysocki, a researcher at a chemical-senses center and an adjunct professor of anatomy at the University of Pennsylvania School of Veterinary Medicine. Sandra Witelson, a neuroscientist at the Michael G. DeGroote School of Medicine at McMaster University in Ontario, Canada, who has studied links between sexual preference and left-handedness, said the Sweden study offers “another important route to look at variation in sexuality.” She said it was significant that lesbian brain responses weren’t just a female version of male heterosexuality, and nor were lesbian brains just a mirror image of the gay male brain. “Sexual orientation may well have a different basis in women than in men,” Witelson said. “It’s not as simple as gay men being more like women, and lesbians being more like men. There are two sexes, which we know are biologically different in some respects, and variation in sexual behavior within each sex is not necessarily the same as in the other sex.” Dr. Louann Brizendine, a UCSF professor of psychiatry and director of a clinic on women’s mood and hormones, said the latest studies “are giving scientists a new handle on the differences” between men and women, as well as gays and straights. How such differences arise needs more research to make clear. So far, Brizendine said, the evidence suggests sex-related differences in brain circuits can be detected in very early childhood, developing perhaps in utero or in early infancy, and that these differences become more pronounced during puberty, when the circuits are shaped further by a burst of sex hormones.

Interesting stuff.