How Well Can You Smell?

Imagine yourself blindfolded and wearing earplugs: Could you follow a chocolate scent with only your nose to guide you?

Surprisingly, most of us can, according to a new study published in Nature Neuroscience this week.

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Researchers put blindfolds, earplugs and gloves on human volunteers, and asked them to find a chocolate scent trail on the ground and track it to the end like a dog would. Researchers found that volunteers could use some of the same smell techniques animals use to follow scent trails.

"We wanted to look at not only if humans could track scent, but how they are able track scent," said Jessica Porter, lead author and a Ph.D. candidate in biophysics at the University of California at Berkeley.

Human Sense of Smell Underappreciated

"'Strawberryness' or 'mintyness' relies on the nose, not the tongue," said Dr. Jay Gottfried, assistant professor of neurology at Northwestern University in Chicago. "Humans rely on smell much more than they appreciate."

"The reason humans have the impression that our smell isn't as good as other animals' is that we use it in such a limited way," said Dr. Gordon Shepherd, professor of neuroscience at Yale University.

People born without the ability to smell highlight the importance of this neglected sensory ability.

"Patients without the ability to smell do suffer a lot. They usually don't know there is a problem until they are kids -- and when others smell that apple pie, but these kids can't," said Gottfried.

"These people without the ability to smell have to ask family members if the milk is spoiled. And they usually cake on cologne or perfume because they are worried they may not be able to detect their own body odor."

Wonders of the Human Sense of Smell

Many animals -- especially dogs -- are known for their keen sense of smell. So how do humans stack up against our canine companions?

"It depends a lot on specifically what you want to compare," said Porter. While dogs can detect many odors at much lower concentrations than humans, "there are examples where humans are actually better. It is not necessarily that the human sense of smell is worse than that of other animals, it is just different."

Humans can detect very small concentrations of certain chemicals, experts said. One example is androstenedione, a compound present in human sweat.

"If you put a drop of it in an Olympic-size swimming pool, a human being is able to tell the difference between the pool with the drop and the pool without it," said Dr. Noam Sobel, associate professor at the Helen Wills Neuroscience Institute and the department of psychology at the University of California at Berkeley.

"This is an astounding ability."

Differences in the ability to detect odors may exist between men and women, experts said.

"Traditionally, women spend more time in the kitchen, and studies have shown that they are generally better smellers than men," said Gottfried. "Women are not necessarily born with a better olfactory sense, it's that they pay more attention to smells because of cooking and putting on perfume."

Why We Have Two Nostrils

Researchers suggest that humans may use their nostrils in a way similar to how they use their ears to locate a sound.

"If you drop a coin on the floor, you know where to look," said Sobel. "The brain converts auditory information into spatial information. The brain does a very fast computation to tell you where things are."

Similarly, the human brain takes advantage of different sensory input from the right and left nostril to locate the smell.

Researchers found that when subjects have one nostril plugged, their ability to follow the scent trail is much worse. "Two nostrils worked better than one," said Porter.

"The two nostrils are two completely different sensors," said Sobel. "Two nostrils can give you spatial information."

Not only could most of us follow a scent trail using two nostrils, our sniffing ability improves with practice.

"With a little training, the volunteers in the study got quite a bit better," said Shepherd. "This raises the question that if humans had training, maybe they'd do a lot better."

Understanding How We Smell May Save Lives

While we have trained dogs on police forces to sniff out clues. Could humans also be expected to sniff out narcotics at an airport? Probably not, said researchers.

However, "if you understand how people follow a scent trail, maybe you can build a scent-tracking robot to detect landmines," said Porter.

While having sniffing robots is not an immediate reality, researchers at Berkeley hope to use findings from studies such as this to make robots that will be able to perform dangerous tasks -- such as locating mines -- using robotic noses.

"These types of study tell us that human sense of smell is more important to everyday experience than most people appreciate," said Gottfried. "There are ways of improving it simply through experience, attention and practice."

So for now, perhaps we should all stop and smell the roses.