for National Geographic News
Eew, where's that smell coming from?
If you could ask a rat, it could locate the direction of the stench's source in a single sniff, scientists report in a new study.
Rats accomplish this feat by effectively smelling in stereo: Each nostril operates independently of the other, sending different signals to the brain that are then computed to determine the direction of the odor.
Stereo sniffing likely gives rats a leg up in everything from tracking down a meal to evading an enemy, said Upinder Bhalla, a neuroscientist at the National Center for Biological Sciences in Bangalore, India.
"Imagine you have a predator sneaking up on you. If you can smell in stereo, you can detect and localize it in one sniff, and you'll have a decent chance of getting away," he said in an email interview.
"If you have to look around, or take multiple sniffs to find the predator, you may get eaten."
Bhalla is a co-author of the study reported in today's issue of the journal Science.
The study, Bhalla said, provides insight into the spatial dimension of smell and the speed at which the brain operates.
"This [finding] helps to constrain and refine our ideas about information processing," he said.
Once trained, rats in the study could determine the direction of a smell in as little as 50 milliseconds, which, Bhalla said, "really is quite fast." According to a 1992 study, one sniff takes humans about 700 or more milliseconds to process.
To establish that rats smell in stereo, Bhalla and colleagues trained thirsty rats to lick different water spouts after they detected the smell of banana, citrus, or rose water. The smell was piped in through a hole in a special chamber.
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