The differences were pronounced. For example, the right cerebral hemisphere in heterosexual men was 624 cubic centimeters -- 12 cubic centimeters greater than the left side. In homosexual men, the right hemisphere was 608 cubic centimeters -- 1 cubic centimeter smaller than the left.
In heterosexual women, there was no volume difference between right and left hemispheres. But in homosexual women, their right hemisphere was 5 cubic centimeters larger than the left.
Next, researchers used positron emission topography to measure blood flow in the amygdala, a brain area involved in processing emotions. The circuitry of the amygdala in gay men more closely resembled that of straight women than straight men, researchers said. The amygdalas of gay women looked more like those of straight men, the report said.
Savic said she thought the brain differences originated in the womb or infancy, probably as a result of genetic or hormonal factors. She said she could not explain why the differences were more pronounced in homosexual men than in homosexual women.
S. Marc Breedlove, a Michigan State University neuroscientist who studies sexual development, said that in his studies with rats, changes in prenatal levels of testosterone caused the sort of brain alterations that Savic observed.
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denise.gellene@latimes.com
