Hopes by the fragrance industry, among others, of finding human pheromones were dashed several years ago when it emerged that a tiny structure in the nose through which mice detect many pheromones, the vomeronasal organ, is largely inactive in humans, having lost its nervous connection with the brain.
Mice are known to influence each other's sexual behavior through emission of chemicals that act like hormones on the recipient's brain and so are known as pheromones. The new finding, if confirmed, would break ground in two important directions, those of human pheromones and human sexuality. But both findings suggest that the hypothalamus is organized in a way related to sexual orientation. LeVay, which is a mere millimeter or so across. The brain scanning technique used by the Swedish researchers lacks the resolution to see the region studied by Dr. Simon LeVay that a small region of the hypothalamus is twice as large in straight men as in women or gay men. The finding is similar to a report in 1991 by Dr. Savic said that she had also studied gay women, but that the data were "somewhat complicated" and not yet ready for publication. Savic reports, as if the hypothalamus's response is determined not by biological sex but by the owner's sexual orientation.ĭr. The gay men responded to the two chemicals in the same way as did women, Dr. The Swedish researchers have now repeated the experiment but with the addition of gay men as a third group. The two chemicals seemed to be leading a double life, playing the role of odor with one sex and of pheromone with another. 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. 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 estrogen-like compound, though it activated the usual smell-related regions in women, lighted up the hypothalamus in men. Savic and colleagues showed that the two chemicals activated the brain in a quite different way from ordinary scents. 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. 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. Ivanka Savic and colleagues at the Karolinska Institute in Stockholm.
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. 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 may open the way to studying human pheromones, as well as the biological basis of sexual preference. 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.