from the May 10th edition of the

THE NATION

Gay, Straight Men's Brain Reaction to Odor Differs

From Newsday

May 10, 2005

MELVILLE, N.Y. — There are odors that drive a person's sexual response, and scientists have found that homosexual men differ from heterosexual men in the way they respond to such smells. Their brain activity more closely resembles the responses observed in women, new research has shown.

"This is another piece of evidence that the brains of gay and straight people are organized differently," said Simon LeVay, a biologist who almost 15 years ago identified a structural difference in the brains of homosexual and heterosexual men. "It is a fascinating finding, but still doesn't explain the origins of sexual orientation."

The new work, by Ivanka Savic and her colleagues at the Karolinska Institute in Stockholm, grew out of an earlier finding that brain scans of men and women differed dramatically from each other in response to chemical smells that mimic male and female hormones.

In their latest study, published in the Proceedings of the National Academy of Sciences, the researchers put gay men into a brain-scanning machine and saw that the region of the anterior hypothalamus became activated when the men were given male sex hormones to smell. Heterosexual men showed more brain activity in this region when smelling odors associated with female hormones.

The smells were made by reconstructing chemicals in male perspiration and female urine that mimic derivatives of testosterone and estrogen.

The brains of the homosexual men showed similar responses to that of heterosexual women when sniffing testosterone. The brains were no different from heterosexual men and women when responding to a nonsexual smell, lavender. The homosexual men reacted to estrogen in the same way they responded to lavender, Savic said.

She says her finding does not suggest that they found a difference in the brain itself, "just that the response is different." Researchers are repeating these studies in homosexual women.

The study shows "that there is a neurobiological difference between gay and straight men," said Sandra Witelson, a neuroscientist at McMaster University in Ontario, Canada.