Just one sniff is all it takes for a rat to tell whether an odour comes from the left or the right, new research reveals, suggesting rats smell in stereo. The rodent impressed scientists in the lab by processing the location of a smell in a mere 50 milliseconds.
Researchers have long sought to understand how human brains pick up on the source of a scent, but their experiments remain limited by the resolution of brain scanning technologies.
Upinder Bhalla of the University of Agricultural Science in Bangalore, India, says that more precise tests can be conducted on rats, using specialised brain and nose probes. “In rats we can do the experiment definitively, monitoring exactly when they’re sniffing, “says Bhalla.
Bhalla and his colleagues exposed rats to various odours and recorded information via probes in the animals’ olfactory bulb, the region of the brain called that first processes smells. They found that 90% of the cells in this brain region respond differently depending on whether a scent first enters the left or right nostril.
Behavioural experiments further revealed rats’ capacity to smell in stereo. The rodents were placed in cages lacking water for brief stretches and given a smelling task. These animals would poke their noses into a hole in the cage wall to pick up on odours sprayed from either the right or left.
The smell of success
If the scent came from the right the rats would receive water by licking the spout on the same side. An odour from the left would likewise precede a water reward from licking the left spout. See one of the rats in swift-whiffing form, here (Mpeg format, 8.5MB, courtesy of Science).
Bhalla and his team selected three scents, which resembled bananas, rose water and eucalyptus. These odours would waft through the lab, so it made sense to pick pleasant ones, he explains. “We have to live with the scents, too.”
With enough training, the rats could accurately guess which spout held the water treat about 90% of the time. Moreover, they could do this within 50 milliseconds – just one sniff. But surgically closing the right or left nostril brought the animals’ accuracy down to just slightly better than chance - around 60%.
The scientists say that smelling in stereo has an evolutionary advantage: it allows the rats to detect the location of a predator or prey with greater precision and speed. Bhalla says that with this spatial sense of smell rats can more easily avoid cats and locate their next meal.
Journal reference: Science (DOI: 10.1126/science.1122096)
NewScientist.com
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