( Researchers have presented the first cl...)Nose odors and mouth odors: The brain distinguishes

Researchers have presented the first clear evidence that olfaction is uniquely a "dual" sense, in that the brain perceives the same odorant molecule differently if it arrives through the nose rather than the mouth. In the August 18, 2005, issue of Neuron, researchers report that the smell of chocolate activated different brain regions according to whether the odor was introduced into the olfactory system through the mouth or through the nose.

In a joint research effort led by Dana M Small of The John B Pierce Laboratory and Yale University and Thomas Hummel of the University of Dresden Medical School, the researchers launched their exploration into the brain's possible dual response to odors because of the well-known phenomenon that sensing an odor "orthonasally" through the nose triggers the perception that it is coming from the outside world, while sensing it through the mouth--or "retronasally"--causes the perception that it arises from the mouth.

"The illusion that retronasally perceived odors are localized to the mouth is so powerful that people routinely mistake retronasal olfaction for 'taste,'" they wrote. "For example, we may say that we like the 'taste' of a wine, because of its fruity or spicy notes. However, gustation refers only to the sensations of sweet, sour, salty, savory, and bitter, and thus the pleasant 'taste' to which we refer is actually a pleasant odor sensed retronasally."

"The role of olfaction in taste is powerful," they said. For example, they pointed out that pinching the nose while eating or drinking--which blocks airflow from the mouth through the olfactory system--blocks flavor perception. Releasing the nose restores the sense of flavor in the mouth.

"The fact that the olfactory referral illusion is maintained even though the subject is now aware that the experience is related to an event in the nose demonstrates that olfactory referral is robust and cognitively impenetrable."

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Source:Cell Press

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