Odor Perception: The Mechanism of How Odor is Perceived

Odor Perception: The Mechanism of How Odor is Perceived

Mitsuo Tonoike (Aino University, Japan)
DOI: 10.4018/978-1-4666-2521-1.ch002


Though olfaction is one of the necessary senses and indispensable for the maintenance of the life of the animal, the mechanism of olfaction had not yet been understood well compared with other sensory systems such as vision and audition. However, recently, the most basic principle of “signal transduction on the reception and transmission for the odor” has been clarified. Therefore, the important next problem is how the information of odors about is processed in the Central Nervous System (CNS) and how odor is perceived in the human brain. In this chapter, the basic olfactory systems in animal and human are described and examples such as “olfactory acuity, threshold, adaptation, and olfactory disorders” are discussed. The mechanism of olfactory information processing is described under the results obtained by using a few new non-invasive measuring methods. In addition, from a few recent studies, it is shown that olfactory neurophysiological information is passing through some deep central regions of the brain before finally being processed in the orbito-frontal areas.
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Olfactory System And Characteristics Of Olfaction

Olfactory Acuity

One characteristic of human olfaction is a very high acuity for odor identification.

Minimum concentrations for the identification of different odors have been defined as “olfactory thresholds” for each odor. Now, gas chromatographs are usually used to detect and evaluate the concentration of an odor. However, this method remains inferior to On the other hand, human olfaction for most odors. In general, olfactory acuity in other animals is considered to be superior to human olfaction; for example, dogs have a high sensitivity and a high acuity for odors. Table 1 (Takagi, 1999) compares the threshold concentrations for detection of various odorants among humans, dogs, and fishes.

Table 1.
Comparison of the threshold concentration for detection of various odorants among human, dogs, and fishes (Takagi, 1999)

The dog’s olfaction shows the threshold of Acetic acid, Butyric acid, and Valeric acid is superior to our human by a factor of about 10-6. The thresholds in some fish are also shown for comparison. On the other hand, the olfactory threshold to β-phenyl ethyl alcohol of the eel may be equivalent to that of the dog.

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