What is Smell?

It might sound like a simple question, but to a scientist, this question is a world of possibilities and wonder.

Smell, more formally known as the olfactory system, is as complicated a phenomenon as sight, touch, or hearing are, but is often overlooked or deemed less important than other senses.[1-2] However, this is starting to change with many researchers and entrepreneurs shifting to accept scent as a sense of primary interest.[2]

The Purpose of Smell

While the sense of smell has many purposes in daily life, such as influencing purchasing decisions or, in the case of its absence, as a telling symptom of COVID-19 infection,[3] its top purpose has to be related to survival.

Imagine not being able to smell a fire, a disaster would soon follow. Even as part of development, smell guides newborns to the source of milk so that they can nurse and get the nutrients they need.[2]

While there are many things that are unique about the biology and perception of smell, it still follows the laws of transduction, the principle that chemical stimuli interact with receptors which are then converted into electrical signals by the central nervous system and relayed to higher-order centers related to perception, memory, and recall. I [4]

Yet, despite dating back billions of years ago, there is still much that remains unknown about the olfactory system.[4] Nevertheless, some hypotheses have been made regarding the earliest evolutionary stages of sense, such as the ability to move away or towards a stimuli depending on its chemical gradient as a large factor for survival.[5]

At a basic level, smell is a sense that allows us to distinguish and identify volatile organic compounds (VOCs).

What Can Noses Do?

As mentioned previously, there are many things our sense of smell can do, below are the major capabilities:

1. Perception: The ability to identify you are sensing an odor.

2. Discrimination: The ability to distinguish between two similar scents, such as milk and dark chocolate.

3. Behavioral Modulation: The phenomenon that odor molecules can dictate behavioral responses, such as dictating food preferences or even synchronizing ovulation cycles between females.[6-7]

4. Integration: The ability to incorporate multiple VOCs into a single scent. For example, chocolate is made up of hundreds of VOCs but we seamlessly integrate the various scent molecules into one single scent, ‘chocolate’.[8]

5. Plasticity: The idea that smell is malleable, changes overtime, and can be shaped by experience.

Thanks to the ability to smell, the brain can deduce a lot of useful and important information about different types of odor stimuli, such as the identity of foods, objects, potential environmental hazards, and even social or emotional cues.[9] With the development of scent recognition technology, this smell can be digitized, quantified, and systematically applied to many industries for various applications.

The Olfactory System

To identify a scent, which is a specific combination of VOCs, an intact olfactory system must be in place. The olfactory system is made up of two basic parts or components, the peripheral and the central.

Two Components of Olfaction in Humans

1. Peripheral: The first part of the scent pathway that enables the initiation of odor perception, mainly consisting of the nostrils, nasal cavity, and the olfactory epithelium which is the sheet that lines the interior of the nose and contains the olfactory receptor neurons that interact with odorants.[4]

2. Central: After transduction, the neuronal pulses are transmitted by the olfactory bulb which then communicates with various cells that signal to other parts of the brain, such as the olfactory cortex, amygdala, the olfactory tubercle, and the hippocampus which is one of the key regions involved in memory formation.[4]

How Smell Works: The Pathway of Scent

Odor molecules enter the nasal cavity and reach the olfactory epithelium, transduction begins. The odors are interpreted as neuronal pulses by the neurons in the epithelium which are then transmitted by the olfactory bulb to other parts of the brain, such as the olfactory cortex, amygdala and the olfactory tubercle which is involved to reward cognition.

Collectively, these systems and processes give rise to our ability to smell and detect odors and tailor our behavior according to what we sense in the environment.

Intermingling Smell and Taste

Olfaction and gustation (taste) overlap and influence each other because odorants can enter from the mouth or nose. This is one of the basic reasons why smell can influence taste and vice versa.[2]

Conclusion

In the world of business and technology, smell is opening doors for possibilities of connecting with the target audience,[10] be it consumers for a heightened experience or with patients for improved care and health monitoring or disease detection.[11]

As COVID-19 has reintroduced the importance of smell on an international level and reminded scientists all over the world that the olfactory system is a key sense that should not be placed on the back burner, placing additional value on the development of scent recognition technology.

At NanoScent, we are happy to be a part of this journey of making scent accessible and quantifiable through our proprietary sensor.

References

1. Gottfried, J.A., 2006. Smell: central nervous processing. Taste and smell, 63, pp.44-69.

2. Auffarth, B., 2013. Understanding smell—The olfactory stimulus problem. Neuroscience & Biobehavioral Reviews, 37(8), pp.1667-1679.

3. Moein, S.T., Hashemian, S.M., Mansourafshar, B., Khorram‐Tousi, A., Tabarsi, P. and Doty, R.L., 2020, August. Smell dysfunction: a biomarker for COVID‐19. In International forum of allergy & rhinology (Vol. 10, No. 8, pp. 944-950).

4. Purves, D., Augustine, G.J., Fitzpatrick, D., Katz, L.C., LaMantia, A.S., McNamara, J.O. and Williams, S.M., 2001. The Organization of the Olfactory System. Neuroscience, pp.337-354.

5. Gottfried, J.A. ed., 2011. Neurobiology of sensation and reward.

6. McClintock, M.K., 1971. Menstrual synchrony and suppression. Nature.

7. Stern, K. and McClintock, M.K., 1998. Regulation of ovulation by human pheromones. Nature, 392(6672), pp.177-179.

8. Counet, C., Callemien, D., Ouwerx, C. and Collin, S., 2002. Use of gas chromatography− olfactometry to identify key odorant compounds in dark chocolate. Comparison of samples before and after conching. Journal of Agricultural and Food Chemistry, 50(8), pp.2385-2391.

9. Zhou, G., Lane, G., Cooper, S.L., Kahnt, T. and Zelano, C., 2019. Characterizing functional pathways of the human olfactory system. Elife, 8, p.e47177.

10. Biswas, D. and Szocs, C., 2019. The smell of healthy choices: Cross-modal sensory compensation effects of ambient scent on food purchases. Journal of Marketing Research, 56(1), pp.123-141.

11. Sankaran, S., Khot, L.R. and Panigrahi, S., 2012. Biology and applications of olfactory sensing system: A review. Sensors and Actuators B: Chemical, 171, pp.1-17.