Nose odors and mouth odors: The brain distinguishes

Researchers have found that for smells that are pleasant to us, such as the smell of chocolate, how we smell is just as important as the smell itself. We can smell both through our noses (duh!) and also through the back of our mouth (who knew?!).

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.”

Dr. John Grohol is the CEO and founder of Psych Central. He is an author, researcher and expert in mental health online, and has been writing about online behavior, mental health and psychology issues -- as well as the intersection of technology and human behavior -- since 1992. Dr. Grohol sits on the editorial board of the journal Cyberpsychology, Behavior and Social Networking and is a founding board member and treasurer of the Society for Participatory Medicine.

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    Last reviewed: By John M. Grohol, Psy.D. on 18 Aug 2005
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