Gay Limbic Reaction to Pheromones
In a study published on May 10, 2005 in The Proceedings of the National Academy of Science , Dr. Ivanka Savic and colleagues at the Karolinska Institute in Stockholm found that homosexual and heterosexual men respond differently to two odors that may be involved in sexual arousal, and that the gay men respond in the same way as women.
An estrogen-like steroid, EST, found in female urine, and a testosterone derivative, AND, found in male sweat, were presented to subjects during a PET scan. While these odors and the odor of cedar produced increased neural activity in the olfactory regions in all subjects, the EST produced an additional response in the anterior portion of the hypothalamus associated with sexual arousal only in heterosexual men, and the AND produced similar arousal only in women and homosexual men.
From the abstract:
These findings show that our brain reacts differently to the two putative pheromones compared with common odors, and suggest a link between sexual orientation and hypothalamic neuronal processes.
From an article about the study in the New York Times:
The gay men responded to the two chemicals in the same way as did women, Dr. Savic reports, as if the hypothalamus's response is determined not by biological sex but by the owner's sexual orientation.
The finding is similar to a report in 1991 by Dr. Simon LeVay that a small region of the hypothalamus is twice as large in straight men as in women or gay men.
If sexual orientation has a genetic cause, or is influenced by hormones in the womb or at puberty, then the neurons in the hypothalamus could wire themselves up in a way that permanently shapes which sex a person is attracted to.
See my previous post Genetic Basis for Sexual Orientation which has links to other relevant information.