Gay Men, Straight Women Have Simi...(men were found to be bigger than the lef...),Health

Fifty of the original participants also underwent positron emission tomography (PET) measurements of blood flow to the brain, designed to analyze connections between the right and left amygdalas. PET scans were performed both while the participants were resting and while they were smelling unscented air.

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 were not related 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.

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