Quote of note:

The Swedish researchers have now repeated the experiment but with the addition of gay men as a third group. 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.

Gay Men Are Found to Have Different Scent of Attraction
By NICHOLAS WADE

Using a brain imaging technique, Swedish researchers have shown 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.

The new research may open the way to studying human pheromones, as well as the biological basis of sexual preference. Pheromones, chemicals emitted by one individual to evoke some behavior in another of the same species, are known to govern sexual activity in animals, but experts differ as to what role, if any, they play in making humans sexually attractive to one another.

The new research, which supports the existence of human pheromones, is reported in today's issue of The Proceedings of the National Academy of Sciences by Dr. Ivanka Savic and colleagues at the Karolinska Institute in Stockholm.

The two chemicals in the study were a testosterone derivative produced in men's sweat and an estrogen-like compound in women's urine, both of which have long been suspected of being pheromones.

Most odors cause specific smell-related regions of the human brain to light up when visualized by a form of brain imaging that tracks blood flow in the brain and therefore, by inference, sites where neurons are active. Several years ago, Dr. Savic and colleagues showed that the two chemicals activated the brain in a quite different way from ordinary scents.

The estrogen-like compound, though it activated the usual smell-related regions in women, lighted up the hypothalamus in men. This is a region in the central base of the brain that governs sexual behavior and, through its control of the pituitary gland lying just beneath it, the hormonal state of the body.

The male sweat chemical, on the other hand, did just the opposite; it activated mostly the hypothalamus in women and the smell-related regions in men. The two chemicals seemed to be leading a double life, playing the role of odor with one sex and of pheromone with another.

The Swedish researchers have now repeated the experiment but with the addition of gay men as a third group. 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.

Dr. Savic said that she had also studied gay women, but that the data were "somewhat complicated" and not yet ready for publication.