Humanos farejadores

Unleash your inner bloodhound – start sniffing
Matéria do New Scientist.

Human subject’s path following a scent trail scent trail of chocolate essential oil through a field (right), as compared to a dog’s scent path of a pheasant dragged through a field (Image: Jess Porter, UC Berkeley)

Humans can follow scent trails across a field in the same way that dogs can – and they improve with practice – a intriguing new field study has revealed.

Jess Porter and Noam Sobel at the University of California in Berkeley, US, and colleagues tested whether 32 people were able to follow a 10-metre-long scent trail of chocolate essence through open grass using only their noses. Two-thirds of them could.

They then trained four of the subjects three times a day for three days over a two week period to see whether they improved with practice. After training the subjects followed the trail more accurately and at more than double the speed. Watch a human sniffer dog in action (2.1MB, requires QuickTime player).

“Once people realised that they could do this, they seemed to develop a good sense of how to zig-zag their noses back and forth across the odour plume in order to pick up the scent most effectively,” says Porter.

Stereo smells

The findings also shed new insight into how mammals smell. Sensory biologists have long-argued about whether mammals compare the scent inputs coming into each nostril in order to localise where a smell is coming from, in the same way they use their left and right ears.

Other animals, such as lobsters, do this by waving their sensor-studded antennae across a scent plume in order to study it, but some had thought that mammalian nostrils were too close together for this to work.

Porter’s team used an imaging technique to establish that the two nostrils do indeed inhale air from distinct, non-overlapping areas of space.

Pick a nostril

Volunteers performed worse at the scent-tracking task when one nostril was blocked, and when they wore a device that conjoined the air input from two separate nostrils into a single “virtual” nostril as it entered the nose.

“It now seems that there’s a common mechanism of scent localization from insects to humans,” says Matthias Laska, a sensory physiologist at Linköping University in Sweden.

As for whether humans could ever get as good as dogs at tracking a scent, Sobel says the biggest problems seems to be getting our noses close to the ground while still being able to move quickly. “Crawling seems to be the rate limiting step,” he says.

The team now plans to study the ability of humans to track scents while standing up.

Journal reference: Nature Neuroscience (DOI: 10.1038/nn1819)