MRI and PET scan studies are showing remarkable similarities between the brains of gay men and straight women, and between those of lesbians and straight men.
For example, the brains of straight men and of gay women share certain common features: both are slightly asymmetric, with the right hemisphere larger than the left, say the Swedish researchers.
On the other hand, the brains of gay men and straight women are both symmetrical.
Similar trends emerged when scientists tracked connectivity in the amygdala, the region of the brain involved in emotional learning and in activating the fight-or-flight response. They noted strong similarities between gay men and straight women, and lesbians and straight men.
The findings are published in the current issue of theProceedings of the National Academy of Sciences.
"This is a very interesting study demonstrating a possible neurobiological relationship in brain size between gay men and straight women," said Paul Sanberg, distinguished professor of neurosurgery and director of the University of South Florida Center for Aging and Brain Repair in Tampa.