Study Shows Lesbian’s Brains React Like Heterosexual Men’s Brains

A team of Swedish researchers at the Stockholm Brain Institute said in the Proceedings of the National Academy of Sciences that lesbians’ brains react differently to sex hormones than the brains of heterosexual women. The team, led by Ivanka Savic, had volunteers sniff pheromones, chemicals derived from male and female sex hormones. Pheromones are known to trigger responses in many animals such as defensive reactions and sexual stimulation. Human response to pheromones has been debated for decades, although American researchers several years ago reported discovery of a gene that may direct a human pheromone receptor inside the nose.

The research, funded by the Swedish Medical Research Council, the Wallenberg Foundation, and the Karolinska Institute, was conducted with three groups of subjects consisting of heterosexual women, heterosexual men, and lesbians. Each of the groups included 12 healthy, right-handed, HIV-negative, unmedicated subjects. The brains of all three groups were scanned while they sniffed male hormones, female hormones, and a set of four ordinary odors. Ordinary odors are usually associated with the basic smell circuits of the brain, while hormones are usually associated with the hypothalamus, which is related to sexual stimulation.

In all the volunteers, the ordinary odors were processed in the brain circuits associated with basic smell. In heterosexual males, the male hormone was processed in the smell area, and the female hormone was processed in the hypothalamus. And in heterosexual women, the female hormone was perceived by the scent area, with the male hormone processed in the hypothalamus. All three groups rated the male hormone more familiar than the female one, and heterosexual women found both hormones to be equally intense. But lesbians and straight men found the male hormone to be more intense and more irritating than the female one, and they liked the female hormone better. Interestingly, in lesbians, both male and female hormones were processed the same, in the basic odor processing circuits.

An earlier study performed by the same team of researchers had indicated that gay men’s brain responses were also different from those of heterosexual men, although the differences in that study were more pronounced than the differences found in the current study. But in both cases the findings support some theories that homosexuality has a physical basis and is not a learned behavior. Sandra Witelson, an expert on brain anatomy and sexual orientation ad McMaster University in Hamilton, Ontario, said that sexual orientation may have a different basis between men and women, and this study does not indicate "just a mirror image situation." Witelson added, "The important thing is to be open to the likely situation that there are biological factors that contribute to sexual orientation."