while it may be neither here nor there,
Lesbian women respond differently than straight women when exposed to suspected sexual chemicals, according to a new brain imaging study.
The finding builds on previous research that suggest that gay men responded in a way more similar to heterosexual women than heterosexual men when exposed to a synthetic chemical.
The natural version of this chemical reportedly appears in high concentrations in male sweat.
The new study extends the research to homosexual women.
It found that lesbians' brains respond in a fashion more similar to that of heterosexual men than of heterosexual women when exposed to the sweat chemical and a synthetic chemical that has been detected in female urine.
"Both studies … indicate that the physiological response in brain regions associated with reproduction are different in homo- and heterosexual persons," Ivanka Savic, a neuroscientist at the Karolinska Institute in Stockholm, Sweden, said in an email.
Savic, who is the lead author of both studies, cautioned that neither study proves people are born gay. The response could be biological or learned. Determining an answer will require further study.
The most recent results were published today in the Proceedings of the National Academy of Sciences.
Savic added that the similarity between homosexual men and heterosexual women seems stronger than the similarity between lesbians and heterosexual men, highlighting the notion that male homosexuality is quite different than female homosexuality.
While pinpointing how homosexual men and lesbians differ requires further study, Savic said, "possibly the lesbian group is more heterogeneous and the mechanisms more diverse."
Smell Test
In the current study, Savic and her colleagues exposed lesbians and heterosexual women and men to a testosterone derivative produced in male sweat known as AND. The subjects were also exposed to an estrogen-like compound called EST found in female urine.
Some scientists believe AND and EST are pheromones, substances emitted by an individual to evoke a specific response in another member of the same species. In many animals, pheromones play a role in sexual attraction.
According to the results, lesbians processed neural responses to AND and EST more like heterosexual men than heterosexual women.
This lends further support to the idea that the chemicals activate the brain differently from common odors, Savic says.
She adds that she and her colleagues are cautious to call the compounds pheromones. In the paper, they call them "candidate compounds for human pheromones."
Charles Wysocki is a member of the Monell Chemical Senses Center and a professor of anatomy at the University of Pennsylvania in Philadelphia.
He says the new study clearly shows that lesbians, heterosexual women, and heterosexual men respond differently to the chemical compounds in male sweat and female urine. But he adds that the response is likely odor-derived and not pheromone-derived.
"The difference across the three groups in response to odors is intriguing, [and] those differences need some sort of explanation," he said.
What Are They Sniffing?
Wysocki disputes the evidence suggesting that AND and EST are pheromones.
"What [evidence] is available comes from the area of entrepreneurial pursuit," he said.
According to Wysocki, California-based entrepreneur David Berliner introduced the compounds into a product he marketed as a way to arouse the opposite sex.
Arousal would come through detection of pheromones with the vomeronasal organ, a bunch of nerve endings in the nasal cavity of some vertebrates believed to be sensitive to pheromones.
"Unfortunately for Dr. Berliner and his group, the whole concept for a functional vomeronasal organ [in humans] has gone down the tubes in the last decade," Wysocki said.
Wysocki's own research, published in September 2005, has shown that gay men prefer odors from other gay men, while odors from gay men were the least preferred by straight men and women.
Had Savic and colleagues obtained their results using real body odors rather than synthetic compounds of the putative pheromones, Wysocki said "that would be phenomenal. I'd be yelling it out."
Michael Meredith is a neuroscientist at the Florida State University in Tallahassee. He too said the results are "very interesting" but added that the suggestion in the paper's title that the compounds are putative pheromones amounts to "spin."
"It doesn't get to the point what the differences in the brain processes are," he said, adding that any argument over whether the brain response results from an odor or pheromone is "just speculation."