Wednesday, May 10, 2006

A quick post about sexy smells

The blog's been a bit fallow lately, so I thought I'd check in even though I'm about to run to class. Lynne brought my attention to this article about pheromone processing in lesbians, aprés a PNAS-reported study that I can't find. (The same team seems to have done a similar experiment on gay and straight men almost exactly a year ago.) The short version: Lesbians process female pheromones differently from straight women, but not exactly the same as straight men. We can file this one under "stuff that was intuitively obvious but that it's nice to have scientific backup for."

The experiment looked at PET scans of gay women (but not straight women, according to this article -- they seem to have been operating off of previously-collected data, which could be a design flaw) while they were exposed to male and female pheromones. Pheromones have even wackier names than most chemicals, names like "4,16-androstadien-3-one" and "estra-1,3,5(10),16-tetraen-3-ol," so we'll use the kindly-provided nicknames AND and EST. Briefly, AND is a pheromone found in all human sweat, but in much higher concentrations in men, and EST is, um, "an estrogen-like substance, found in the urine of pregnant women." Yum.

Here's the purportedly interesting part:
When Savic's team looked at the brain activity of the 12 lesbian women, it found the lesbians responded to both compounds in a similar way. And they processed them in a way more like heterosexual men than heterosexual women. But the relationship to the opposite sex was not as strong as the researchers found it to be in a previous study between homosexual men and heterosexual women.
So lesbians have similar preferences to straight men, and the difference between gay and straight women is not the same as the difference between gay and straight men. In other words, lesbians like girls, and homosexuality in women is not exactly the same as homosexuality in men. Duh and duh, but again, it's nice to have confirmation.

But this is the part I find really interesting:
Savic's group also found that in contrast to the heterosexual women they studied, the lesbian women processed the AND pheromone by the olfactory network, not the anterior hypothalamus; when they smelled the EST pheromone, they partly shared activation of the anterior hypothalamus with the heterosexual men studied.
Now, maybe I'm getting my anterior hypothalamus wrong -- this article only says that it "regulates metabolic process and links the nervous system to the endocrine system by secreting brain hormones." But I always thought that the hypothalamus was related to emotion. If that's not wrong, and a cursory Google search (I told you, I'm on my way to class) implies that it's not, then this is very cool. The article makes it sound like the pheromones of the sex you're attracted to are processed like pheromones, and the others are processed like smells. This is pretty interesting already. But the hypothalmic involvement implies -- and this is very glib, I know -- that the attractive pheromones are processed with an emotional component, an emotional rather than just a physical arousal. That's still saying the same basic thing as "the pheromones of the sex you're attracted to are processed like pheromones, and the others are processed like smells," but with more of a clue as to what "processed like pheromones" means. And a nice implication that emotional arousal and physical arousal are intricately linked. (After all, any emotion traces back to physical structures like the hypothalamus, anyway.)


robin said...

Interesting, your observation about the arousal of the hypothalamus, and its suggestion of a possible connection between emotional and physical arousal in the lesbians' processing of pheromones. But I wonder if this is a response unique to women. Wouldn't it be interesting if males processed pheromones strictly as a physiological response, with no emotional (i.e. hypothalmic) involvement? I realize it plays into a lot of sex stereotypes, but it's just a thought -- and an experiment I'd like to see done, on both homosexual and heterosexual males.

5/11/2006 9:41 AM  
jess said...

Here's what they say in the first article (there's a version of the same paragraph in the second):

In a previous PET study of regional cerebral blood flow (rCBF) in heterosexual subjects (13), we found that smelling AND and EST caused a sex-differentiated activation of the anterior hypothalamus. In women, AND activated the preoptic area and ventromedial nuclei, whereas, in men, activation by EST involved an area covering the paraventricular and dorsomedial nuclei. In contrast, when men smelled AND and women EST, activations were found only in amygdala plus piriform cortex, anterior insular cortex, orbitofrontal cortex, and anterior cingulate cortex. These areas are reported to process the signals of common odors (19, 20, 21), and were possibly recruited by the odor components of AND and EST. Our interpretation of this sex-differentiated pattern of activation was that the two steroid compounds may act bimodally, both as pheromones and odors. We proposed the hypothesis that the anterior hypothalamus primarily processed signals from the pheromone-like component of AND and EST, whereas the olfactory brain primarily mediated the signals of their odor component.

5/11/2006 10:39 AM  

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