From The National Geographic:
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.
More here.