for National Geographic News
Lesbian women respond differently than straight women when exposed to suspected sexual chemicals, according to a new brain imaging study.
The finding builds on previous research that suggest that gay men responded in a way more similar to heterosexual women than heterosexual men when exposed to a synthetic chemical.
The natural version of this chemical reportedly appears in high concentrations in male sweat.
The new study extends the research to homosexual women.
It found that lesbians' brains respond in a fashion more similar to that of heterosexual men than of heterosexual women when exposed to the sweat chemical and a synthetic chemical that has been detected in female urine.
"Both studies indicate that the physiological response in brain regions associated with reproduction are different in homo- and heterosexual persons," Ivanka Savic, a neuroscientist at the Karolinska Institute in Stockholm, Sweden, said in an email.
Savic, who is the lead author of both studies, cautioned that neither study proves people are born gay. The response could be biological or learned. Determining an answer will require further study.
The most recent results were published today in the Proceedings of the National Academy of Sciences.
Savic added that the similarity between homosexual men and heterosexual women seems stronger than the similarity between lesbians and heterosexual men, highlighting the notion that male homosexuality is quite different than female homosexuality.
While pinpointing how homosexual men and lesbians differ requires further study, Savic said, "possibly the lesbian group is more heterogeneous and the mechanisms more diverse."
In the current study, Savic and her colleagues exposed lesbians and heterosexual women and men to a testosterone derivative produced in male sweat known as AND. The subjects were also exposed to an estrogen-like compound called EST found in female urine.
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