- WASHINGTON (AP) - Lesbians' brains react differently to sex hormones than
those of heterosexual women, new research indicates.
- That's in line with an earlier study
that had indicated gay men's brain responses were different from straight
men - though the difference for men was more pronounced than has now been
found in women.
- Lesbians' brains reacted somewhat, though
not completely, like those of heterosexual men, a team of Swedish researchers
said in Tuesday'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.
- 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 at McMaster University in Hamilton, Ontario.
- "The important thing is to be open
to the likely situation that there are biological factors that contribute
to sexual orientation," added Witelson, who was not part of the research
- 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
- Whether humans respond to pheromones
has been debated, although in 2000 American researchers reported finding
a gene that they believe directs a human pheromone receptor in the nose.
- The same team reported last year on a
comparison of the response of male homosexuals 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, but weaker,
relationship between the response of lesbians and straight men.
- 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
- 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.
- The brains of all three groups were scanned
when sniffing male and female hormones and a set of four ordinary odors.
Ordinary odors were processed in the brain circuits associated with smell
in all the volunteers.
- 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.
- In lesbians, both male and female hormones
were processed the same, in the basic odor processing circuits, Savic and
her team reported.
- Each of the three groups of subjects
included 12 healthy, unmedicated, right-handed and HIV-negative individuals.
- The research was funded by the Swedish
Medical Research Council, Karolinska Institute and the Wallenberg Foundation.
- Copyright 2006 The Associated Press.
- Alan Cantwell M.D.
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