All it takes is a few molecules of a certain chemical to enable mammals to smell their own species up to a half-mile away, said Milos Novotny, Distinguished Professor of Chemistry and director of the Institute for Pheromone Research at Indiana University.
The chemicals, called pheromones, are detected by the vomeronasal organ (VNO) in the animal's nose. Unlike the part of the nose that detects ordinary smells, this super-sensitive organ is connected directly to the mid-brain.
"This is the shortest organ-to-brain distance in mammalian biology," Novotny said. "A cascade of biochemical processes can be triggered quite selectively by specific olfactants such as pheromones at incredibly small quantities. Studies of mammalian pheromones can have a significant effect on pest control, promoting endangered species, and, perhaps above all, for understanding our own sense of smell and associated behaviors."
Signals from a mammal's nose caused by normal smells called odorants go to various places in the cortex, in the upper part of the brain, which is why humans are conscious of smells. But pheromone signals go directly to the mid-brain, without being processed by the conscious brain. What happens after that is not completely clear, but there is a lot of evidence that the animal's behavior and hormonal levels are influenced.
In a paper published July 12 in the journal Nature, Novotny and co-workers at Harvard Medical School in Boston headed by Linda Buck reported that the vomeronasal organ can actually detect both odorants and pheromones. The VNO detected odorants classified as animalic, camphoraceous, citrus, floral, fruity, green/minty, musky, sweet or woody. Like pheromones, these odorants were detected at extremely small concentrations.