Courtesy Dr. Mehmet Oz

The Mysterious Sense of Smell

“It’s as plain as the nose on your face” goes a common adage. But the inner workings of the nose and its connection to the brain are anything but obvious.

Last year, researchers at Rice University in Houston set out to learn how our brains process competing smells.

For the study, they fitted two bottles with nosepieces so that volunteers could sample two scents simultaneously—one through each nostril. One bottle contained a type of ethyl alcohol that smells of rose petals, and the other had n-butanol, with a scent similar to marker pens.

What happened? All 12 volunteers reported shifting between smelling roses and getting whiffs of marker pens. Some people switched more frequently and drastically than others, and no predictable pattern was noted across the group or within individuals.

The participants experienced an “olfactory illusion,” said Denise Chen, assistant professor of psychology, who coauthored the research paper with graduate student Wen Zhou. “Instead of perceiving a constant mixture of the two smells, they perceive one of the smells, followed by the other, in an alternating fashion, as if the nostrils were competing with one another. Although both smells are equally present, the brain attends to predominantly one of them at a time.”

Call it the battle of the paired sensory organs. Scientists recognize that a similar type of tug of war occurs in the brain when the eyes view separate images at the same time (one image for each eye) and when processing simultaneous sounds. The finding at Rice University is the first to demonstrate “perceptual rivalry” in the olfactory system.

“Interestingly, scientists say that the response to aromas is influenced by ethnic background, memories, and newly discovered variabilities in the olfactory system,” explained Dr. Oz in the Mar/Apr 2010 Post article “Soothing Scents.” “Our knowledge of the olfactory system—which helps the brain recognize, categorize, and memorize a multitude of smells—has lagged behind our understanding of sight, hearing, taste, and touch.”

Chen’s research is published in the Sept. 29 print edition of the journal Current Biology.

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March 9, 2010