The results of a study using PET and fMRI on three groups of individuals (homosexual males, heterosexual males and females) by Ivanka Savic and colleagues at the Karolinska Institute in Sweden was printed in the journal Neuroscience. The study found that common odors (e.g., cedar, lavender) were processed similarly in all three groups of subjects and engaged only the olfactory brain (amygdala, piriform, orbitofrontal, and insular cortex). But when confronted by AND, a testosterone compound, portions of the anterior hypothalamus, brain areas related to sexual activity, showed activity in straight women and in gay men, but not in straight men. These findings showed that the human brain reacts differently to putative pheromones compared with common odors, and suggest a link between sexual orientation and hypothalamic neuronal processes. Although it is premature to classify AND and EST (an estrogen compound) as pheromones, the data suggest that they may function as chemosignals.
Abstract at: http://www.pnas.org/content/102/20/7356