Navigation Links
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."

To begin to penetrate the neural cause of olfaction's duality, the researchers devised the first experiments to directly compare the same odorants introduced through the nose and the mouth.

"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 ing the possibility that odorant administration interacts with experience to engage unique brain regions and that olfactory referral induced by retronasal stimulation creates a differential reward context for food but not for non-food odors by signaling availability versus receipt of food," they concluded. "Because the current study tested only one food, future experiments are needed to determine whether other food odors produce the same differential brain activations," they wrote.

However, the researchers found that the two different chemicals butanol and farnesol did not elicit significantly different brain responses according to the route of delivery, indicating that the properties of the molecules do not play a role in the response.


Source:Cell Press

Related biology news :

1. Study shows humans have ability to track odors, much like bloodhounds
2. Researchers find link between food odors and lifespan in fruit flies
3. Trio of plant genes prevent too many mouths
4. Have a taste for fat? Yes! A sensor in the mouth promotes preference for fatty foods
5. Dartmouth study finds that arsenic inhibits DNA repair
6. GlycoFi and Dartmouth report full humanization of yeast glycosylation pathway in Science
7. UF scientists discover new genus of frogmouth bird in Solomon Islands
8. Controversial drug shown to act on brain protein to cut alcohol use
9. Mouse brain cells rapidly recover after Alzheimers plaques are cleared
10. Mouse brain tumors mimic those in human genetic disorder
11. New imaging method gives early indication if brain cancer therapy is effective, U-M study shows
Post Your Comments:

(Date:6/16/2016)... The global Biometric ... USD 1.83 billion by 2024, according to a ... proliferation and increasing demand in commercial buildings, consumer ... the market growth.      (Logo: ... of advanced multimodal techniques for biometric authentication and ...
(Date:6/9/2016)... leader in attendance control systems is proud to announce the introduction of fingerprint attendance ... the right employees are actually signing in, and to even control the opening of ... ... ... Photo - ...
(Date:6/7/2016)... -- Syngrafii Inc. and San Antonio Credit Union (SACU) ... Syngrafii,s patented LongPen™ eSignature "Wet" solution into SACU,s ... in greater convenience for SACU members and operational ... document workflow and compliance requirements. Logo ... Highlights: ...
Breaking Biology News(10 mins):
(Date:6/23/2016)... - FACIT has announced the creation of a ... Propellon Therapeutics Inc. ("Propellon" or "the Company"), to ... of first-in-class WDR5 inhibitors for the treatment of ... an exciting class of therapies, possessing the potential ... patients. Substantial advances have been achieved with the ...
(Date:6/23/2016)... ... June 23, 2016 , ... Charm Sciences, Inc. is ... has received AOAC Research Institute approval 061601. , “This is another AOAC-RI approval ... Bob Salter, Vice President of Regulatory and Industrial Affairs. “The Peel Plate methods ...
(Date:6/23/2016)... , June 23, 2016   EpiBiome , ... secured $1 million in debt financing from Silicon Valley ... up automation and to advance its drug development efforts, ... new facility. "SVB has been an incredible ... the services a traditional bank would provide," said Dr. ...
(Date:6/23/2016)... ... ... In a new case report published today in STEM CELLS Translational Medicine, ... after being treated for breast cancer benefitted from an injection of stem cells derived ... debilitating, frequent side effect of cancer treatment. , Lymphedema refers to the ...
Breaking Biology Technology: