by Bob Roehr

Two separate pieces of research on odors and how the brain processes them have strengthened the case that, at least for gay men, there is a strong biological component to sexual orientation.

The studies involved odors and pheromones, chemical signaling molecules that are processed through a set of receptors in the nose and nerve connections to the brain. Each of the two systems is separate but parallel. Smells are processed in olfactory regions of the brain while pheromones are processed in the hypothalamus, a more primitive portion of the brain that regulates sexual activity.

Earlier work by Ivanka Savic and colleagues at the Karolinska Institute in Sweden, using brain imaging techniques, had demonstrated that when males were exposed to a testosterone derivative, the olfactory regions of their brains lit up but not the hypothalamus. They were processing the molecular signals as smells and not in a sexual manner.

Males showed exactly the opposite pattern when exposed to derivatives of estrogen.

Females in the study showed the reverse pattern. As expected, they processed exposure to female hormones as smells and male hormones in the hypothalamus.

Dr. Savic repeated the experiment, this time throwing a group of exclusively gay men into the mix. She found that the brains of gay men processed the hormonal stimulus in the same way as females, not as males.

The study was published in the May 17 edition of the prestigious Proceedings of the National Academy of Sciences.

The findings are compatible with those made in 1991 by Simon LeVay. By conducting autopsies of the brain, he found that a small region of the hypothalamus in gay men was similar in size to that of women. That same region of the brain was twice as large in heterosexual men.

The second piece of evidence comes from a team led by Charles J. Wysocki at the non-profit Monell Chemical Senses Center near Philadelphia. It was released early and will be published in the September issue of Psychological Science. That study used gauze pads to carefully gather sweat from the armpits of heterosexual males and females, as well as exclusively gay men and lesbians. The researchers used the pads and liquids to create an eau de sweat, which they placed inside small plastic bottles.

A different set of members from those four population groups were recruited and told simply that the experiment was to assess their preference for body odors; there was no mention of gender or sexual orientation. They were asked to take a sniff from the numbered bottles, two at a time in various dictated combinations, and say which of the pair they preferred.

When all of the data was processed, gay men were the odd ones out. They clearly preferred the body odors generated by other gay men, with a lesser preference for that of heterosexual females. Heterosexual males and females, as well as lesbians preferred odors from heterosexual males relative to gay males.

In a nose-to-nose comparison of the scents of heterosexual females and lesbians, the heteros clearly were preferred by three of the four groups. Heterosexual males were more ambivalent, which may help to explain the allure of girl-on-girl action in straight porn.

To Wysocki, the overall data suggests “that lesbians and gay males may produce an array of axillary [armpit] odorants that distinguish them from heterosexual. Furthermore, gay males may perceive the characteristic odorants different from their heterosexual counterparts.”

In addition, it suggests “that odor choice is primarily driven by the participants’ perceptions of perceived odor pleasantness or unpleasantness, and that perceived pleasantness is determined, in part, by gender and sexual orientation,” he said.