Human Noses Sort Out Strangers, Friends

(HealthDay News) -- Dogs aren't the only ones who can sniff out interlopers.

Humans have a far more sophisticated sense of smell than previously believed and can use their nose to differentiate between a friend and a stranger, say Canadian researchers at the McGill University's Montreal Neurological Institute (MNI).

While placed in a PET scanner, study volunteers were asked to identify four different odors: their own, a friend's; a stranger's; and a normal or common everyday odor. The PET scan results showed that body odors are processed by an entirely different nerve pathway in the brain than normal/common odors.

The researchers also found that a stranger's body odor activates the same brain regions (amygdala and insular cortex) that respond to fear and danger.

"Our study demonstrates that the olfactory system has preferential processing for behaviorally important stimuli," lead investigator Dr. Johan Lundstrom, former postdoctoral fellow at the MNI, said in a prepared statement.

"This means that stimuli that are perceived as very important for us -- either for our survival, finding food, or [they] are carrying other important signals, such as mate selection signals -- are processed faster and more accurately by specialized neuronal networks. It is known that the auditory and visual systems work in much the same way, and we have now demonstrated this for the olfactory system," said Lundstrom, currently Assistant Member at the Monell Chemical Senses Center in Philadelphia.

"This explains why participants perceived a stranger's body odor as more intense and less pleasant than the other odors. A stranger's body odor is a behaviorally important stimulus, because it is unfamiliar and might signal danger. Therefore, the brain has developed a mechanism to ensure that it grabs our attention," Lundstrom said.

The study is published in the current issue of Cerebral Cortex.

More information
The Social Issues Research Center in the U.K. has more about the human sense of smell.