STOCKHOLM: The brains of lesbians react differently to sex hormones than those of heterosexual women, a new study has shown.
Following an earlier study which showed differences in how homosexual and heterosexual men's brains respond to sex-linked pheromones, the new study by a team of Swedish scientists examined how the brains of women who identified as lesbian were stimulated when they smelled the same substances.
The researchers focused on the brain's anterior hypothalamus, where reproductive functions are mediated, said the study published online Monday by the Proceedings of the National Academy of Sciences.
Researchers tested reactions to the pheromones 'AND', a progesterone derivative found in men's sweat, and 'EST', an estrogen-like substance found in the urine of pregnant women.
They found that in positron emission topography examinations of the brains of 12 gay women, smelling AND mainly stimulated their olfactory networks, or senses of smell.
But in heterosexual women, the hormone stimulates the anterior hypothalamus.
On the other hand, when the lesbians smelled EST, the reaction in the anterior hypothalamus was more similar to those of heterosexual men.
The study also noted that unlike heterosexual men and women, and homosexual men, the olfactory systems of lesbians did not react markedly differently to smelling AND or EST.
The study, by scientists of the Karolinska University Hospital in Stockholm, followed an earlier one in which they measured the response of homosexual men to the two pheromones.
In that study they determined that gay men showed marked similarities in their brain responses to those of heterosexual women. The study emphasised, too, that those similarities were significantly greater than the congruence between the lesbian and heterosexual men reactions.
"Very little is currently known about the physiology of female homosexuality. However, if the chemosensory processing of AND and EST is related to sexual orientation rather than the biological sex, the pattern of activation in lesbian women would be expected to deviate from that of heterosexual women," the study said.
"These data suggest that the observed difference between lesbian women and heterosexual women reflects a physiological process."
A summary of the study further noted that "The results add further evidence to the idea that AND and EST are pheromones involved in sexual preference, and also highlights the notion that male homosexuality is quite different than female homosexuality."