New Scientist published an article on May 8, 2006 titled "Clue to Sexual Attraction Found in Lesbian Brain" about a research study recently published in Proceedings of the National Academy of Sciences:
"Lesbian and heterosexual women respond differently to specific human odours, a brain-scanning study has found. The homosexual women showed similar brain activity to heterosexual men when they inhaled certain chemicals, which may be pheromones, the researchers say.
Lead researcher Ivanka Savic at the Karolinska Institute in Stockholm...and her colleagues asked 12 lesbian women and 12 heterosexual women to breathe concentrated samples of two steroids: EST, which is derived from estrogen and found in the urine of pregnant women; and AND, which is derived from progesterone and found in men's armpit sweat...
When the heterosexual women smelled AND their brains showed activity in the anterior hypothalamus, a region of the brain thought to process sexual cues. But EST only produced activity in the olfactory region of their brains, the area that processes smells. The lesbians, however, only showed activity in the olfactory region whichever odour they smelled. The researchers conclude that these 'pheromone-like stimuli' produce different responses in the anterior hypothalamus of women of different sexual orientations, and that their research supports the idea that the anterior hypothalamus plays a role in sexual preference." May 8, 2006 New Scientist
The Associated Press released an article on May 9, 2006 titled "Lesbians' Brains Respond Like Straight Men," which stated:
"Lesbians' brains react differently to sex hormones than those of heterosexual women, new research indicates...Lesbians' brains reacted somewhat, though not completely, like those of heterosexual men, a team of Swedish researchers said in Tuesday's edition of Proceedings of the National Academy of Sciences...
The findings add weight to the idea that homosexuality has a physical basis and is not learned behavior.
The research team led [by] Ivanka Savic at the Stockholm Brain Institute had volunteers sniff chemicals derived from male and female sex hormones. These chemicals are thought to be pheromones - molecules known to trigger responses such as defense and sex in many animals. Whether humans respond to pheromones has been debated, although in 2000 American researchers reported finding a gene that they believe directs a human pheromone receptor in the nose.
Heterosexual women found the male and female and pheromones about equally pleasant, while straight men and lesbians liked the female pheromone more than the male one. Men and lesbians also found the male hormone more irritating than the female one, while straight women were more likely to be irritated by the female hormone than the male one." May 9, 2006 Associated Press
Ivanka Savic-Berglund, MD, PhD, Associate Professor at the Centre of Gender-Related Medicine at the Karolinksa Institute in Stockholm, Sweden, published a paper in the Proceedings of the National Academy of Sciences on May 16, 2006 titled "Brain Response to Putative Pheromones in Lesbian Women":
"The progesterone derivative 4,16-androstadien-3-one (AND) and the estrogen-like steroid estra-1,3,5(10),16-tetraen-3-ol (EST) are candidate compounds for human pheromones. In previous positron emission tomography studies, we found that smelling AND and EST activated regions primarily incorporating the sexually dimorphic nuclei of the anterior hypothalamus, that this activation was differentiated with respect to sex and compound, and that homosexual men processed AND congruently with heterosexual women rather than heterosexual men.
These observations indicate involvement of the anterior hypothalamus in physiological processes related to sexual orientation in humans. We expand the information on this issue in the present study by performing identical positron emission tomography experiments on 12 lesbian women. In contrast to heterosexual women, lesbian women processed AND stimuli by the olfactory networks and not the anterior hypothalamus.
Furthermore, when smelling EST, they partly shared activation of the anterior hypothalamus with heterosexual men. These data support our previous results about differentiated processing of pheromone-like stimuli in humans and further strengthen the notion of a coupling between hypothalamic neuronal circuits and sexual preferences." May 16, 2006 Ivanka Savic-Berglund