By Randolph E. Schmid Associated Press

Gays’ and lesbians’ brains respond differently from those of straight men and women when exposed to sex hormones, but researchers now say the difference is less pronounced in lesbians than in gay men.

Lesbians’ brains reacted somewhat like those of heterosexual men, a team of Swedish researchers said in the 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. In both cases the findings add weight to the idea that homosexuality has a physical basis and is not learned.

“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. “The important thing is to be open to the likely situation that there are biological factors that contribute to sexual orientation,” added Witelson.

The same team reported last year on a comparison of the response of gay men to heterosexual men and women. They found that the brains of gay men reacted more like those of women than of straight men. The new study shows a similar relationship between the response of lesbians and heterosexual men. 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.

In heterosexual males the male hormone was processed in the scent area but the female hormone was processed in the hypothalamus, which is related to sexual stimulation. In straight women the sexual area of the brain responded to the male hormone while the female hormone was perceived by the scent area.

This article appeared in the Dallas Voice print edition, May 26, 2006. siteэтапы проведения рекламной кампании