Humans show odor-tracking skill

NEW YORK – By studying blindfolded college students who crawled through grass to sniff out a chocolate-scented trail, scientists say they’ve found evidence of a human smelling ability that experts thought was impossible.

The study indicates the human brain compares information it gets from each nostril to get clues about where a smell is coming from. And it suggests dogs, mice and other mammals do the same thing, contrary to what most scientists have thought.

People compare signals from each ear to locate the source of a noise. But the prevailing notion has been that mammals can’t follow the same strategy for smells, because their nostrils are too close together to get distinct signals.

“We debunked that,” said Noam Sobel of the University of California, Berkeley, who reported the new results Sunday with graduate student Jess Porter and others on the Web site of the journal Nature Neuroscience. The work will appear in the journal’s January issue.

The new paper reports five experiments. One was designed to see if people could use just their noses to follow a 30-foot-long trail of chocolate scent. The trail was created with scented twine, and undergraduate students at Berkeley were blindfolded and equipped with thick gloves, kneepads and elbow pads to make sure they couldn’t see or feel it.

Researchers found that the 14 volunteers did better at following the scent of chocolate if they used two nostrils than if one nostril was taped shut. They succeeded 66 percent of the time with two nostrils, versus 36 percent with one nostril.

But did that really mean their brains were benefiting from two independent signals? To sort that out, researchers retested four of the participants. This time, the subjects wore devices over their nostrils that controlled the airflow into their noses.

The participants were less successful and slower when they had the equivalent of one nostril. That supports the idea that people benefit from having two, researchers said.