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environment general science genetics health and medicine space technology January 27, 2003 
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Making Sense of Science

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Smart Nose (video)
November 07, 2002

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Interviewees: Noam Sobel, University of California - Berkeley; Joel Mainland, UC Berkeley.

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Produced by Brad Kloza

Copyright © ScienCentral, Inc., with additional footage courtesy of Maurizio Corbetta.

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Neuroscience for kids - smell experiment

Do you smell with your nose or your brain?

Scientists have been wondering that for years. As this ScienCentral News video reports, new tests show it's not the nose, but the brain that knows.

Clearing the air

“What’s that smell?” your friend asks, sniffing into the air and wrinkling his nose. If you couldn’t detect a fulsome odor, you might wonder if he’s imagining things. But actually, the problem could be in your head. Neuroscientists at the University of California Berkeley now believe that for some of us, our brains have to learn to smell certain odors.
About 30 percent of the population does not detect an odor when they sniff androstenone (which functions as a sex pheromone in wild pigs). But Noam Sobel, a professor working in the Berkeley Olfactory Research Project (BORP), can smell it from 30 feet away when it is sealed inside jars (it smells awful--“like dirty laundry,” he says).

At first scientists assumed this was a genetic flaw, something akin to color blindness. But in 1989 researchers at the Monell Chemical Senses Center discovered that, with practice and time, non-detectors could learn to smell androstenone. What was not known, however, was whether this learning was happening in the odor receptors in the nose, or in the olfactory cortex in the brain.

Sobel and grad student Joel Mainland set out to test this by replicating the 1989 study of training non-detectors to smell androstenone. But this time, they blocked one of the subjects’ nostrils, effectively training only one nostril to learn the smell.

“The idea here is simple,” says Sobel. “If the untrained, unexposed nostril learns to detect androstenone, then the learning must have occurred at a higher level, at the brain.”

Their results, published in the journal Nature, revealed that the un-exposed nostrils of non-detectors learned just as well as the exposed ones.

“The message from the peripheral nose to the brain was always the same when the person couldn’t, and later could, detect the odor,” says Sobel. “The brain, over time, learned how to make sense of a previously senseless [message].”

The plastic brain

The ability of the brain to acquire a capability it previously did not have is referred to as “plasticity.” Brain scientists are finding that adult brains are more malleable than previously thought, and understanding plasticity has become a central theme of neuroscience.

“Ideally, if you were to understand the mechanisms underlying this phenomenon you would eventually be able to repair the injured nervous system,” says Sobel. “One of the major goals of neuroscience is to repair an injured nervous system or brain. And in order to do that artificially you would want to first understand how that happens naturally, how the system regenerates on its own.”

Studies like this suggest that it merely takes sustained practice to force the brain to do something we had assumed it could not do. For example, stroke patients who lose the use of one side of their body can often regain the capability by literally tying down the good side and forcing the brain to relearn how to use the bad side.

“Here we have another instance of that,” says Sobel. “If we force the brain to do something it doesn't usually do, it can actually gain capabilities, even in the adult.”

Sobel next hopes to use magnetic resonance imaging to find the location of this plasticity and watch it happen in the brain. His work was funded by the National Institute on Deafness and Other Communication Disorders and the Sense of Smell Institute.

by Brad Kloza

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