Based on the results of a PET study, lesbians have very little in common with their own gender and only some similarities with heterosexual men when it comes to their response to sexual stimuli.
In their ongoing research on sexual orientation and brain response, Dr. Ivanka Savic and colleagues from the Karolinska Institute in Stockholm, Sweden, took a closer look at the physiology of female homosexuality.
In a previous paper, the group determined that certain areas in a gay man's brain responded to a hormone found in male sweat the same way straight women did. This suggested a "link between sexual orientation and hypothalamic neural processes" (Proceedings of the National Academy of Sciences, May 17, 2005, Vol. 102:20, pp. 7356-7361).
In the latest study, Savic and colleagues conducted a similar olfactory-based PET study in 36 healthy lesbians, heterosexual women (HeW), and heterosexual men (HeM). During the PET scans, regional cerebral blood flow (rCBF) was measured while the subjects smelled (not sniffed) three stimuli: the steroid AND (4,16-androstadien-3-one) found in male sweat; the steroid EST (estra-1,3,5[10],16-tetraen-3-ol), which is similar to estrogen; and four ordinary odors (OO), including lavender oil and butanol. The PET images were reformatted and coregistered with MRI scans and filtered with a 10-mm Gaussian kernel.
According to the results, the lesbian subjects showed activation patterns in the amygdala, the piriform, and the insular cortices (odor-processing circuits) when smelling AND and EST. More importantly, their brains' did not differentiate between the two compounds. In contrast, HeW and HeM processed AND in the anterior hypothalamus, while the olfactory regions were involved when smelling EST.
"The hypothalamic activation in HeM covered the dorsomedial and paraventricular nuclei. In HeW, it covered the preoptic area and the ventromedial and tubermammillary nuclei," the authors explained. There was "an absence of preoptic activation with AND in lesbian women," they added (PNAS, May 16, 2006).
The preoptic area of the brain reacts to hormonal and sensory cues that are necessary for sexual behavior, the group stated.
To investigate a possible accord between lesbian women and HeM with respect to hypothalamic engagement, a posthoc volume of interest (VOI) analysis was done. In lesbians, the VOI analysis revealed a "significant interaction" between all stimuli in the dorsomedial and paraventricular hypothalamus. However, HeM only saw those areas activated by EST.
"The main observation in the present study is that lesbian women differed from HeW in that they did not activate the preoptic hypothalamus with AND," the group wrote. "Furthermore, the lesbian women shared a hypothalamic cluster with the HeM when smelling EST.... The observed difference between lesbian women and HeW reflects a physiological process ... indicating that our lesbian subjects process the stimuli from AND as odors rather than pheromones." On the other hand, lesbian women processed EST and AND as odors whereas HeM processed EST as a pheromone.
By Shalmali Pal
AuntMinnie.com staff writer
May 30, 2006
Related Reading
Ontario goes courting gay U.S. doctors, September 8, 2005
Sweat scent study suggests gay men's brains differ, May 11, 2005
No faking female orgasm in scientific research, June 20, 2005
Will Etheridge's breast cancer up screening in gay community?, October 15, 2004
Sexual healing: Imaging takes a roll in the hay with human relations, May 29, 2004
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