Scientists have found evidence of a response to pheromones in the human brain, a new report says. These volatile compounds--secreted by one member of a species to elicit a response (either behavioral or physiological) from another individual--and their use in communication has long been documented in lower mammals such as rodents and pigs. But now, in a study published in the August 30 issue of the journal Neuron, scientists at Huddinge University Hospital in Sweden have detected a pheromone effect in humans.

Ivanka Savic and colleagues used positron emission tomography (PET) to scan the brains of 12 men and 12 women while the subjects smelled synthetic versions of compounds related to the hormones estrogen and testosterone. The estrogen compound caused the men to experience increased blood flow to the hypothalamus, the region of the brain rodents use for pheromone detection, but had no effect on the women. The testosterone-related compound, meanwhile, caused heightened blood flow in the women, but not the men.

Such gender-specific reactions in the brain lend strong support to the theory that humans can detect pheromonal signals, although the exact pathway for detection is as yet unknown. Indeed, the researchers concede that the existence of human pheromones remains an open question but believe their current study calls for "further, extensive research of chemosensory signals in humans."