On the scent

New Scientist, 08 January 2000

PEOPLE feel differently about a smell depending on which nostril they sniff it through, say scientists in the US.

Larry Cahill of the University of California at Irvine and his colleagues asked 32 volunteers to sniff eight common odours, including lemon and peppermint. The volunteers had to smell the odours through one nostril and rate them for pleasantness on a scale of -5 to +5, and also try to identify them. They came back later to repeat the test with the other nostril.

When a smell was inhaled through the right nostril, it was rated on average as more pleasant than when sniffed through the left. But the left nostril was more accurate when the volunteers were trying to identify what they were breathing in.

Cahill says the findings fit with ideas about how the brain processes smells. Earlier research suggested that each nostril sends almost all its sensory information to its own side of the brain. Because the right hemisphere of the brain controls emotional processing, this could explain why smells might be perceived to have a different degree of pleasantness when sniffed through the right nostril.

"Your emotional reaction to an odour actually depends on which hemisphere does the processing," Cahill concludes. He hopes to use brain imaging to watch how the two hemispheres respond to the same odour.