UNLEASH your inner bloodhound and start sniffing. Humans can follow scent trails in the same way as dogs 鈥� and they improve with practice.
Jess Porter and Noam Sobel at the University of California, Berkeley, and their colleagues asked 32 people to follow a 10-metre scent trail (yellow line in Photo) of chocolate essence through open grass using only their noses. Two-thirds of them could (red line in Photo).
They then trained four volunteers three times a day for three days to see whether they improved with practice. After training, the subjects followed the trail more accurately and at more than double their initial speed (Nature Neuroscience, DOI: 10.1038/nn1819). 鈥淥nce people realised they could do this, they seemed to develop a good sense of how to zigzag their noses back and forth across the odour to pick up the scent most effectively,鈥� says Porter.
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The findings provide new insights into how mammals smell. Sensory biologists have long argued about whether mammals compare the scent inputs entering each nostril in order to pinpoint where a smell is coming from, in the same way as they use their ears. Other animals, such as lobsters, do this using their sensor-studded antennae, but mammalian nostrils were thought to be too close together for this to work.
Porter鈥檚 team shone a laser on particles entering people鈥檚 nostrils to establish that the two nostrils do indeed inhale air from distinct areas of space. What鈥檚 more, volunteers did worse at the scent-tracking task when one nostril was blocked or when they wore an artificial single nostril that equalised the air input to their two real nostrils.
鈥淚t now seems that there鈥檚 a common mechanism of scent localisation from insects to humans,鈥� says Matthias Laska at Link枚ping University in Sweden.
As for whether humans could ever get as good as dogs at tracking a scent, Sobel says one of the biggest problems seems to be getting our noses close to the ground while still being able to move quickly. 鈥淐rawling seems to be the rate-limiting step,鈥� he says. But the work supports earlier claims that training can work wonders on our sense of smell (see 麻豆传媒, 24 December 2005, p 56).
