Lesbians' brains reacted somewhat, though not completely, like those of heterosexual men, a team of Swedish researchers said in today's edition of Proceedings of the National Academy of Sciences.

A year ago, the same group reported findings for gay men that showed their brain response to hormones was similar to that of heterosexual women.

"It shows sexual orientation may very well have a different basis between men and women ... this is not just a mirror image situation," said Sandra Witelson, an expert on brain anatomy and sexual orientation at the Michael G. DeGroote School of Medicine at McMaster University in Hamilton, Ontario.

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.

Heterosexual women found the male and female 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.

All three groups rated the male hormone more familiar than the female one. Straight women found both hormones about equal in intensity, while lesbians and straight men found the male hormone more intense than the female one.

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