Lesbian girls have a different brain structure

It is no news that people who have unconventional sexual orientation look differently. However the study showed that they also think differently.

Lesbians’ brains react differently to sex hormones than those of heterosexual women. An earlier study of gay men also showed their brain response was different from straight men — an even stronger difference than has now been found in lesbians.

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 behavior.

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.

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 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.

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, according to the AP.

Larger populations need to be studied, Savic said. When asked if her research suggests that programmes to change sexuality would not be effective, she said: "We have no proof, but I anticipate in the majority of people these programmes will not work."

Others debate the meaning of the new research.

"It certainly suggests biological processes are at play," said Brian Mustanski, an assistant professor in the department of psychiatry at the University of Illinois at Chicago . "And they certainly could be intersecting with some sort of environmental effects." Health24.com reports.

Although Savic told one reporter that her data suggest programs that attempt to change sexual orientation likely would not work for most people, she was careful not to attribute sexuality to differences in the brain. Rather than sexual orientation being determined by neural biology, the opposite may instead – or also – be true: that learned behavior influences brain anatomy and physiology, ebar.com says.