( penetrate the neural cause of olfaction...)Nose odors and mouth odors: The brain distinguishes

"Although several studies have examined brain responses to retronasal olfactory stimulation, none have directly compared orthonasal and retronasal stimulation in the same subjects or considered the possibility that the effects of route of stimulation depend on the way that odors are typically sensed," wrote Small and her colleagues. "For example, food odors are normally experienced both orthonasally and retronasally, whereas nonfood odors are perceived only orthonasally. Therefore, it is possible that the route of stimulation may have different effects for food versus nonfood odors."

In their experiments, they inserted small tubes into the noses of volunteers such that one tube ended at the nostrils and the other ended farther back in the nasal passage near the throat, where odors from the mouth would originate. As they introduced odors into one tube or the other, they scanned the subject's brains using functional magnetic resonance imaging, a technique in which harmless magnetic fields and radio waves detect increased blood flow to brain areas, which reflects increased activity.

They used four odorants: chocolate odor represented a food odor, and lavender represented a non-food odor that was similarly pleasant as chocolate. They also chose two odorant chemicals--butanol and farnesol--to test a theory that the olfactory system distinguishes molecules according to whether they are more water soluble (butanol) or oily (farnesol).

The researchers found that the chocolate odor, indeed, activated different brain regions according to the route of administration, supporting the duality of olfaction. The lavender odor did appear to activate different regions, but to a far lesser extent.

"The effect of route of delivery was greatest for the chocolate odor, rais
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Source:Cell Press