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Science Sniffs Out the Secrets of Scent

Brain translates a mix of chemicals into what the nose knows

WEDNESDAY, June 14, 2006 (HealthDay News) -- When you stop to smell the roses, what you are actually doing is using nerve cells in the brain's olfactory bulb to identify and combine together a host of chemicals that your brain then registers as "a rose."

So concluded researchers at Duke University Medical Center, whose study in mice found that complex smells are not detected by the brain as just a single object or smell.

"We wanted to understand how the brain puts together scent signals to make an odor picture. We discovered the whole is the sum of its parts," researcher Da Yu Lin said in a prepared statement.

Since humans and mice have similar olfactory bulbs used to detect smells, the researchers suggest that the human brain may process complex scents in the same manner.

During the study, the Duke team tracked the reaction of neurons in the olfactory bulb when mice were exposed to different smells. Neuron activity was captured using intrinsic signal imaging, which notes light changes with a sensitive camera.

The mice sniffed a variety of complex compounds, including peanut butter, coffee and fresh urine, as well as the individual chemicals that make up the complex smells.

"We found that glomeruli, the functional units of the olfactory bulb, act as detectors for individual compounds. There are no single detectors for complete smells," said Lin.

Reporting in the June 16 issue of Neuron, Lin's team concluded that the brain creates a sort of "odor picture" based on the compilation of chemical components that make up a scent. They also noted that this information is most likely sent to a more complex area of the brain where the scent can be decoded and recognized.

This process in which the brain perceives a recognized scent from multiple compounds may offer insight into how humans perceive other complex stimuli --including sight and sound, the researchers said.

More information

Visit the Monell Chemical Senses Center to read more about how the brain processes senses.

SOURCES: Duke University Medical Center, news release, June 14, 2006
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