A potential pheromone found in male perspiration activates the brains of homosexual men and heterosexual women in a similar manner, researchers report.

While it is unclear if humans respond to pheromones, candidate compounds include a testosterone derivative called 4,16-androstadien-3-one (AND), and the estrogen-like steroid estra-1,3-5(10),16-tetraen-3-ol (EST).

In a previous study, Ivanka Savic and colleagues demonstrated that the hypothalamus region of the brain becomes activated when men smell EST and women smell AND, but not vice versa.

In the current study, the researchers examined whether brain activation patterns induced by EST and AND corresponded with sexual orientation, rather than with biological gender. The scientists compared brain activity between homosexual men, and heterosexual men and women, in response to smelling EST, AND, and ordinary odors, such as lavender.

The researchers observed that AND activated the hypothalamus in homosexual men and heterosexual women, but not heterosexual men. Conversely, EST activated the hypothalamus in heterosexual men alone. All three groups responded to common odors similarly, engaging only brain regions that process smell. 

These findings indicate that the human brain reacts differently to these potential pheromones compared with common odors, suggesting a link between sexual orientation and brain function.

PNAS highlights for the week of May 9 - 13

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