Olfactory fatigue

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Olfactory fatigue, also known as odor fatigue, olfactory adaptation, and noseblindness, is the temporary, normal inability to distinguish a particular odor after a prolonged exposure to that airborne compound.[1] For example, when entering a restaurant initially the odor of food is often perceived as being very strong, but after time the awareness of the odor normally fades to the point where the smell is not perceptible or is much weaker. After leaving the area of high odor, the sensitivity is restored with time. Anosmia is the permanent loss of the sense of smell, and is different from olfactory fatigue.

It is a term commonly used in wine tasting, where one loses the ability to smell and distinguish wine bouquet after sniffing at wine(s) continuously for an extended period of time. The term is also used in the study of indoor air quality, for example, in the perception of odors from people, tobacco, and cleaning agents.

Olfactory fatigue is an example of neural adaptation or sensory adaptation. The body becomes desensitized to stimuli to prevent the overloading of the nervous system, thus allowing it to respond to new stimuli that are 'out of the ordinary'.

Olfactory fatigue is when the sense of smell is blocked. This could happen for many reasons but sometimes it's simply because there are too many smells going on.[2] Some people may begin to lose their sense of smell around age 50.[3] Smell is recognized with different codes that are created in the olfactory system. Smell is categorized as a primary sensory organ.[4] When a person is trying to smell something many different things are involved in order to figure out what it is.[5][4] Our brains have to recall what this scent is from and sometimes our other senses are also involved such as taste.

Olfactory receptors are triggered by the nose or mouth. Olfactory fatigue happens so that we can smell other things and so the nervous system does not fill completely.[5] Sense of smell is a key sense in our lives and some people rely on it heavily. Even though this is a very complex system with many different ideas of how it all works together.[2] When fetuses are just being developed the first sense they could use is smell.[3]

Mechanism[edit]

After olfactory neurons depolarize in response to an odorant, the G-protein mediated second messenger response activates adenylyl cyclase, increasing cyclic AMP (cAMP) concentration inside a cell, which then opens a cyclic nucleotide gated cation channel.[6] The influx of Ca2+ ions through this channel triggers olfactory adaptation immediately because Ca2+/calmodulin-dependent protein kinase II or CaMK activation directly represses the opening of cation channels, inactivates adenylyl cyclase, and activates the phosphodiesterase that cleaves cAMP.[7] These series of actions by CaMK, desensitizes olfactory receptors to prolonged odorant exposure.

An ORNs or an Olfactory Receptor Neuron alert goes off to detect the smell. When the nose is covered out taste is a lot harder because the air we breathe goes into our nose as well. A common idea is that vanilla smells sweet and that is because we taste sweet when we eat vanilla flavorings.[8]

Improving olfactory sense[edit]

Olfactometric method and clinical studies[edit]

Sachs mentions the earliest reference as old as early nineteenth century. The primitive stages in curing the condition in humans were through the clinical experiments. The Elsberg method was one of the first to determine the threshold value for odorous substances. To date, his olfactometric method is known as one of the best methods to stimulate the threshold of olfactory senses and determine the decaying of the senses once there has been a continuous supply of same smell.

Rejuvenation through coffee[edit]

Some perfumers stock coffee beans near their displays as it is commonly believed that smelling coffee between perfume testing can limit or reverse olfactory fatigue.

This view remains controversial, with some researchers citing positive reactions while subsequent research seems to indicate no benefit from sniffing coffee beans compared to lemons scents or plain air:

  • "smelling coffee not only refreshes olfactory sensory receptors but also stimulates appetite. Our effort to smell coffee beans for about 3–4 min after cooking enabled our sensory smell to be refreshed and thereby increasing our appetite greatly."[9][unreliable medical source?]
  • "Smelling coffee aroma between perfume samples, as compared to smelling unscented air, actually works. The perceived odor intensity of the perfume from sample to sample stayed the same after smelling coffee aroma while it decreased when smelling air between samples. The pleasantness of the perfume, however, was similar after smelling coffee or air."[10]
  • "Fragrance sellers often provide coffee beans to their customers as a "nasal palate cleanser," to reduce the effects of olfactory adaptation and habituation. To test this idea, college students smelled three fragrances multiple times, rating odors each time. After completing nine trials, participants sniffed coffee beans, lemon slices, or plain air. Participants then indicated which of four presented fragrances had not been previously smelled. Coffee beans did not yield better performance than lemon slices or air."[11]

Rejuvenation through other means[edit]

Another commonly believed way to reduce olfactory fatigue is to smell one's own unperfumed skin (typically the crook of the elbow) on the theory this is the "baseline" smell for each individual.[citation needed]

See also[edit]

References[edit]

  1. ^ Odors chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2005
  2. ^ a b "What is Olfactory Fatigue? Do you have it?". ChemDAQ Incorporated. 2018-02-19. Retrieved 2019-02-26.
  3. ^ a b Sarnat HB, Flores-Sarnat L, Wei XC (May 2017). "Olfactory Development, Part 1: Function, From Fetal Perception to Adult Wine-Tasting". Journal of Child Neurology. 32 (6): 566–578. doi:10.1177/0883073817690867. PMID 28424010.
  4. ^ a b Auffarth B (September 2013). "Understanding smell--the olfactory stimulus problem". Neuroscience and Biobehavioral Reviews. 37 (8): 1667–79. doi:10.1016/j.neubiorev.2013.06.009. PMID 23806440.
  5. ^ a b Saito N, Yamano E, Ishii A, Tanaka M, Nakamura J, Watanabe Y (2018-03-29). Roman G, ed. "Involvement of the olfactory system in the induction of anti-fatigue effects by odorants". PLOS One. 13 (3): e0195263. doi:10.1371/journal.pone.0195263. PMC 5875884. PMID 29596487.
  6. ^ Chen TY, Yau KW (April 1994). "Direct modulation by Ca(2+)-calmodulin of cyclic nucleotide-activated channel of rat olfactory receptor neurons". Nature. 368 (6471): 545–8. Bibcode:1994Natur.368..545C. doi:10.1038/368545a0. PMID 7511217.
  7. ^ Dougherty DP, Wright GA, Yew AC (July 2005). "Computational model of the cAMP-mediated sensory response and calcium-dependent adaptation in vertebrate olfactory receptor neurons". Proceedings of the National Academy of Sciences of the United States of America. 102 (30): 10415–20. Bibcode:2005PNAS..10210415D. doi:10.1073/pnas.0504099102. PMC 1180786. PMID 16027364.
  8. ^ Auvray M, Spence C (September 2008). "The multisensory perception of flavor". Consciousness and Cognition. 17 (3): 1016–31. doi:10.1016/j.concog.2007.06.005. PMID 17689100.
  9. ^ Dorri Y, Sabeghi M, Kurien BT (2 March 2007). "Awaken olfactory receptors of humans and experimental animals by coffee odourants to induce appetite". Medical Hypotheses. 69 (3): 508–9. doi:10.1016/j.mehy.2006.12.048. PMID 17331659.
  10. ^ Secundo L, Sobel N (June 2006). "The influence of smelling coffee on olfactory habituation". Chemical Senses 2006. 31 (5): A52–A52.
  11. ^ Grosofsky A, Haupert ML, Versteeg SW (April 2011). "An exploratory investigation of coffee and lemon scents and odor identification". Perceptual and Motor Skills. 112 (2): 536–8. doi:10.2466/24.PMS.112.2.536-538. PMID 21667761.

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