Washington – Gay men’s brains respond differently from those of heterosexual males when exposed to a sexual stimulus, researchers have found.
The homosexual men’s brains responded more like those of women when the men sniffed a chemical from the male hormone testosterone.
“It is one more piece of evidence … that is showing that sexual orientation is not all learned,” said Sandra Witelson, an expert on brain anatomy and sexual orientation at the Mi chael DeGroote School of Medicine at McMaster University in Ontario, Canada.
Witelson, who was not part of the research team, said the findings clearly show a biological involvement in sexual orientation.
The study, published in today’s issue of Proceedings of the National Academy of Sciences, was done by researchers at the Karolinska Institute in Stockholm, Sweden.
They exposed heterosexual men and women and homosexual men to 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.
When they sniffed smells like cedar or lavender, the subjects’ brains reacted only in the olfactory region that handles smells.
When confronted by a chemical from testosterone, the male hormone, portions of the brains active in sexual activity were activated in straight women and in gay men but not in straight men, the researchers found.
The response in gay men and straight women was concentrated in the hypothalamus, particularly in the area that is active in hormonal and sensory responses necessary for sexual behavior, the researchers said.
