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Gay and Straight Men React Differently to Sexual Odors


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Interesting article. I copied the entire article as you must be signed up to view (NY Times)


Published: May 9, 2005

Using a brain-imaging technique, Swedish researchers have shown that men and women respond differently to two odors that may be involved in sexual arousal, and that homosexual men respond in the same way as women.

The two chemicals, one a testosterone derivative produced in men's sweat and the other an estrogen-like compound found in women's urine, have long been suspected of being pheromones, chemicals emitted by one individual to trigger some behavior in another of the same species. The role of pheromones, particularly in guiding sexual behavior, has been well established in animals but experts differ as to what importance, if any, they have retained in human mating.

The new research may open the way to studying human pheromones as well as the biological basis of sexual preference. The study, by Dr. Ivanka Savic and colleagues at the Karolinska Institute in Stockholm, is being reported in Tuesday's issue of the Proceedings of the National Academy of Sciences.

Most odors cause specific, smell-related regions of the human brain to light up when visualized by a PET scanner, a form of brain imaging that tracks blood flow in the brain and hence, by inference, the presence of suddenly active neurons in need of extra glucose. 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, lit up the hypothalamus in men. This is a brain center 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.

Dr. Savic has now repeated the experiment but with the addition of homosexual men as a third group. The gay men responded to the two chemicals in the same way as did women, she reports, as if the hypothalamus's response is determined not by biological sex but by the owner's sexual orientation.

Dr. Savic said she had also studied homosexual women, and had gathered "very interesting and somewhat complicated preliminary data." Another researcher said that it did not matter that gay women were not included in Dr. Savic's final report because they do not respond in the same way as gay men do.

The report by Dr. Savic and her colleagues recalls a 1991 report by Dr. Simon LeVay that a small region of the hypothalamus was twice as large in straight men than in women or gay men. The PET scanning technique used by Dr. Savic lacks the resolution to see the region studied by Dr. LeVay, which is a mere millimeter or so across. But both findings suggest that the hypothalamus is organized in a way related to sexual orientation.

The new finding, if confirmed, would break new ground in two important directions, those of human pheromones and human sexuality. Mice are known to influence each other's sexual behavior through emission of chemicals that act like hormones on the recipient's brain and are known, by derivation, as pheromones. Hopes, by the fragrance industry among others, of finding human pheromones were dashed several years ago when it emerged that the vomero-nasal organ, a tiny structure in the nose through which mice detect many pheromones, has largely lost its innervation in humans.

Researchers interpreted that to mean that humans, as they evolved to rely more on sight than on smell, had no need of the primitive cues that pass for sexual attractiveness among mice. But a role for human pheromones could not be ruled out, especially in light of findings that women living or working together tend to synchronize their menstrual cycles.

Dr. Savic's work is seen by some researchers as strong evidence in favor of human pheromones. "The question of whether human pheromones exist has been answered. They do," Dr. Noam Sobel, a neuroscientist at the University of California, Berkeley, wrote in commenting on Dr. Savic's report of 2001.

Dr. Catherine Dulac, a Harvard University biologist who studies pheromones in mice, said that if a chemical modified the function of the hypothalamus, that might be sufficient to regard it as a pheromone. She said the Swedish study was extremely interesting, even though "humans are a terrible experimental subject," but noted the researchers had used a far higher dose of the armpit chemical than anyone would be exposed to in normal life.

If human pheromones do exist, Dr. Savic's approach may allow insights into how the brain is organized not just for sexual orientation but for sexuality in general. "The big question is not where homosexuality comes from but where does sexuality come from," said Dr. Dean Hamer, a geneticist at the National Institutes of Health.

The different pattern of activity that Dr. Savic sees in the brains of gay men could be either a cause or an effect of their sexual orientation. 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 shaped which sex a person is attracted to. Alternatively, Dr. Savic's finding could be just be a consequence of straight and gay men using their brain in different ways.

"We cannot tell if the different pattern is cause or effect - the study does not give any answer to these crucial questions," Dr. Savic said. But the technique might provide an answer, Dr. Hamer noted, if it were applied to people of different ages to see when in life the different pattern of response developed.

Dr. LeVay said he believed from animal experiments that the size differences in the hypothalamic region he had studied arose before birth, perhaps in response to differences in the circulating level of sex hormones. Both his finding and Dr. Savic's suggest the hypothalamus is specifically organized in relation to sexual orientation, he said.

Some researchers believe there is likely to be a genetic component of homosexuality because of its concordance among twins. The occurrence of male homosexuality in both members of a twin pair is 22 percent in non-identical twins but rises to 52 percent in identical twins. On the other hand, gay men have fewer children, meaning that in Darwinian terms any genetic variant that promotes homosexuality should be quickly eliminated from the population. Dr. Hamer believes such genes may nevertheless persist because, although they reduce descendants in gay men, they increase fertility in women.

Could Dr. Savic's technique be used as a way of assessing a person's sexual orientation? She said it had not be shown to have the specificity necessary for a test. Other researchers said that observing people's reactions to erotic images was a simpler way of doing the same thing, so the brain scanning technique raised no new issues.

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I was listening to the cbc yesterday morning. There was a great long stretch where they were talking about an old WWII and Cold War era military machine. This machine was developed to detect homosexuals so they could be purged from the military and civil service.

The name of the machine...

"The Fruit Machine"

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I heard some of that too - something about measuring pupil dilation and so on flashing pictures in front of people. If I remember correctly, they didn't stop using it until just a couple of decades ago, when they decided it was hopelessly unreliable.

yep. parts of it are on display at the war museum, [color:purple]another proud moment in war history...

if you hit sites like the New York Times that want an account, thy username & password cyberpunk. seems to work most everywhere :)

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