Return of the ‘gay brain’

News that a neuroimaging study has found that the brains of gay participants more closely resemble those of their straight, opposite sex counterparts is being widely reported, but one of the most interesting details is largely being ignored.

The study was completed by neuroscientists Ivanka Savic and Per Lindstrom and had two parts.

The first and most widely reported part compared the brain structure of 25 homosexual men, 25 heterosexual men, 20 homosexual women and 20 heterosexual women.

The punchline is that in a measure of brain symmetry, straight men and gay women were similar, and gay men and straight women were similar.

But this isn’t the most interesting part in itself. Structural brain differences between gay and straight participants have been reported before, although this new study was better designed as it included both males and females.

What is most intriguing about this new study is a further investigation assessed amygdala function in each side of the brain. In particular, it looked at the balance of activity between the two hemispheres when the participants were asked just to breath in unscented air.

The study found that straight men and gay women had greater right sided activity, whereas gay men and straight women showed equal activation on both sides. As with the structural comparisons, the measurements from homosexual participants were similar to their straight, opposite sex counterparts.

The reason this new study is interesting is because it found a functional brain difference in a task that was not specifically linked to sex or attraction.

Previous studies have found functional differences in the brains of gay and straight people, but they have tended to use experiments where participants were presented with either sexual images, gender specific faces, or stimuli linked to sexual activity, such as pheromones.

These are interesting findings, but they may be the result of same-sex sexual activity, rather than an explanation for why people seek it out.

If you have experience of sleeping with same-sex partners, it’s hardly surprising that you may have a different response to same-sex material.

These new findings were from a neutral task. Now it’s possible that lots of same sex experience could affect your brain response to fresh air, but it’s highly unlikely.

It is possible, of course, that same-sex experience could alter the function of specific brain circuits which affects even non-sex related tasks, but these results also suggest the possibility that some more general differences in brain organisation are responsible for a number of effects, including sexual orientation.

This last explanation is what the researchers suggest, and it is another clue that sexual orientation is not simply the result of experience.

Of course, it’s not definite proof, but it is an interesting and important pointer.

Link to abstract of study.
Link to write-up from New Scientist.