Gay Men, Straight Women Have Similar Brains

Here again, lesbians appeared to react more like straight men, while gay men were more like straight women.

According to the authors, fight-or-flight reactions -- controlled in part by the amygdala -- are more common in men than in women.

The differences, which werenotrelated to sexual attraction, could be due to environmental effects, genetics or the influence of sex hormones, the study authors stated.

Although some sex differences in brain size are visible at birth, the brain continues to develop as the child matures, meaning that environmental factors could also play a role.

The current wisdom regarding genetics and sexual orientation posits that genes may play a role in male homosexuality but not in female homosexuality, the researchers said.

Experts have also speculated that exposure to sex hormones prenatally influence sexual preference. Male rhesus monkeys have more androgen (a male sex hormone) receptors in the right side of the brain, while females have an equal distribution of receptors for the hormone.

And brain asymmetry in male rats is established by early exposure to androgens. Symmetry in female brain hemispheres can be reversed by removing the ovaries soon after birth.

This study does little to clarify the reasons behind the differences, the researchers added, although it certainly does add to the debate.

More information

There's more on how the brain works at The Franklin Institute.

SOURCES: Paul Sanberg, Ph.D., D.Sc., distinguished professor of neurosurgery and director, University of South Florida Center for Aging and Brain Repair, Tampa; Keith A. Young, Ph.D., associate professor of psychiatry and behavioral science, Texas A&M Health Science Center College of Medicine, and co-director, Central Texas Veterans Health Care System Neuropsychiatry Research Program, Waco and Temple, Texas;Proceedings of the National Academy of Sciences, June 16-20, 2008