Bring Up Smell- How We Perceive Odours

We are now well into Spring, and walking outside is totally blissful. The temperature is comfortable, but more importantly, the scent in the air is somehow exhilarating. I then stop walking and take a moment to breathe in all the odours that surround me. I am fortunate enough not to be afflicted by any pollen allergies, so I go all out. I can smell flowers, freshly mown grass, dirt, laundry and more. Not only is the smell keeping me connected to the present, but it is also igniting an interior feeling of deep connection to my surroundings. This connection is bringing me its share of joy and tranquility. I know that as long as I’ll be standing right here, everything will remain perfect.

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Our sense of smell, or olfaction, is (as far as we know) our oldest sense, right along with taste. It is such a remarkably developed sense that we are able to detect a tremendous number of odours. Despite what a study from 1927 suggested, humans have the potential to smell much more than 10,000 distinct odorants. Over one billion of them, to be exact, as reported by a 2014 study. Still, this incredible figure is considerably meagre compared to the ability displayed by dogs. Our domesticated canines are surpassing our smelling power by as much as 44 fold (44x), with 220 million olfactory receptor cells in their nasal cavity compared with 5–6 million for us, mere humans.

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In comparison to the senses presented in two earlier posts (see Bring Up Hearing, Bring Up Sight), smell possesses a rather simple organ, the nose. This cavity has receptors spread over all of its epithelium. These receptors are cranial neurons that are astonishingly capable of renewing themselves every 30–60 days. Neurons are typically incapable of such feats. The nasal cavity encompasses a wide diversity of cells. It includes no less than six morphologically and biochemically distinct cell types. One especially relevant cell type for smell is the ciliated cells. Their sensory cilia are facing the inside of the nasal cavity. Their role is to catch the odorant molecules. Once activated, they send their signal to the olfactory cortex in the main olfactory bulb (there are two). The second olfactory bulb, called the vomeronasal organ (VNO), is not as important as the main. It serves to detect pheromones. In humans, we can find our VNO in the anteroinferior third of the nasal septum. The VNO also signals to the main olfactory bulb.

To be fair, all odours, scents, and pheromones are volatile compounds. However, pheromones have something that odours and scents do not have. Pheromones are chemical substances secreted by one individual and absorbed (or received) by another individual of the same species. The pheromones, once someone else picks them up, can act as hormones in their body. They have the ability to alter behaviour and physiology for survival and reproduction purposes. There are many kinds of pheromones, each carrying different signalling objectives. The signal emitted could be used to signal danger, food ingestion safety, food location and more, which can promote survival. As for reproduction, they can signal for potential and fertile mates and help with offspring recognition.

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When it comes to choosing sexual partners, Smell seems to be a significant component for determining their attractiveness. Indeed, some studies have demonstrated that family members seem to have a scent perceived as “less attractive” compared with the scent of strangers. It is actually quite understandable as inbreeding correlates to an increased susceptibility to a wide range of disorders. Limiting inbreeding through regulating smell perception may seem like a reasonable solution to deter us from it. However, smell perception may not serve the unique purpose of limiting inbreeding. It also helps to recognize who’s family and who’s not. And we are able to do this very early on in life. Newborns are capable of identifying their mothers after being exposed for at least one hour.

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The sense of smell is not as stable as the other senses; it varies greatly depending on conditions. In general, women have more robust, or more attuned, olfactory abilities compared to men. Although, this might not be true. Recent researchers have now started questioning this “common knowledge” and its validity. They have revealed that the difference noticed between the sexes is actually really small and possibly caused by anatomical differences. Now omitting the weakly possible sex differences, there are still other factors influencing olfactory variation. Circadian rhythm seems to be a strong influence; early morning appears to be accompanied by the weakest sensitivity to smell. Scientists are suggesting that its highest point is at night, right before going to bed. At last, an important factor seems to be the availability of moisture in our nasal cavity. The more, the merrier it seems. With this idea in mind, researchers are now advancing that smell is at its best during summer and spring. Workout sessions also seem to work wonders when it comes to increasing olfactory power.

It’s all well and good to know how our olfaction changes, but why should we care about it enough to protect it? The reason is utterly simple; it makes us feel great. Although, this is possible only if we perceive the scents as pleasant. From all the senses, olfaction is the one that shares the most links to memory and emotional brain regions. There is a belief in the activation of olfactory neurons to have the capacity to activate the brain reward system, which is a system also involved in addictive behaviours. Smell, as well as taste, is considered to have developed this strong connection as a way to avoid ingesting potentially harmful substances or running straight towards danger. By reinforcing survival behaviour through rewards, we are now not only able to safely feed ourselves, but we can also enjoy the process. Actually, if you didn’t already know, smell has a lot to do with taste as it provides 80% of the signalling necessary to perceive flavours. Another curious thing about smell resides in how our body responds to its signals. For most senses, when signals reach the brain, there will first be its identification, and only then would it be followed by a reaction. Olfaction works the other way around, reaction (emotional) first and then identification after.

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When smell was introduced to you as having a lot to do with pleasure, some of you might have been quite skeptical. However, we did not produce that theory out of thin air and without anything to back it up. It turns out that people with olfactory dysfunctions tend to struggle more with malnutrition, apathy, depression and lower quality of life than the general population. This statement potentially indicates that a disrupted perception of scents leads to an overall decrease in hedonia (pleasure, enjoyment and comfort). These olfactory dysfunctions can be a reduced sense of smell (Hyposmia), a total lack of olfaction (Anosmia), a change in its perception (Parosmia, things that usually smell pleasant might now smell bad) or a perception of a smell that is actually not present (Phantosmia, olfactory hallucination). These dysfunctions could be present at birth or occur at any moment in our life. The general advice is to avoid excessive exposure to malodours (bad smells) as it can lead to the onset of a dysfunction.

At last, we are part of the mammalian family, and as such, we can infer that the ownership of a nose is not exclusive to only us but also to the rest of the family. If you also thought as much, then you wouldn’t be completely wrong. Most mammals have or had a nose, and still, not all of them use it as their primary olfactory organs. Toothed whales still have a nose but can’t smell anymore. Baleen whales, however, have kept the usage of their nose as an olfactory tool. Albeit we don’t know about the precise purpose of keeping them as they strongly rely on echolocation to find food. Other animals likewise can smell, but they might not smell the same way we do. Snakes, for example, smell mainly through their VNO located at the roof of their mouth, even though they also have a nose capable of sensing odours. They grab the molecules of scents with their tongue and insert them into the VNO for identification. As for fish, they do smell through an olfactory organ located in their nasal sac, where water, filled with chemical signals, is flowing in. As water comes in, it makes contact with the lamellae possessing olfactory receptor neurons which can provide the fish with the necessary information. Considerably more animals have olfaction than those that do not, which only encourages us to consider its importance towards our survival. Would you not agree?

I thank you infinitely for reading this post and if you would like to know more about the mysteries that surround us, please join my subscription list to keep up with my newest content. If you have any questions, please add them to the comment section and I’ll make sure to answer as soon as humanly possible.

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Bring Up Biophilia—What makes us particularly attracted to nature

No one can dismiss the amazing feeling we get after spending some time in nature. We instantly feel relaxed and reinvigorated. Some might attribute this effect to time spent far away from work, and even though they could be correct, it is not the whole picture. Biophilia is a relatively new concept that brought the…

Bring Up Blood—How our oxygen gets carried throughout our body

Good evening my dearest followers, Please, take a moment to enjoy this excerpt for my newest post (Bring Up Blood). We could most certainly not live without blood. It is absolutely essential for the survival of our most distant limbs and organs. Even though almost all of our respiration is thanks to our respiratory organs,…

Bring Up Hearing—Where is this sound coming from

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The type of stimulus that first recruits my awareness in the morning is most probably auditory. The sound may be coming from outside, like bird songs, or it could be coming from indoors, like my scheduled alarms. It certainly sounds more pleasant to be awakened by the tweeting of the birds, but living in Montréal, hearing the rumblings of heavy machinery is definitely more likely, which is sincerely irritating. This observation raises a particular question about the pleasantness of sounds and its origin. To answer the how and where its pleasantness comes from, we must know the differences between music and noise. However, it may not be as straightforward a question as it may seem.

The nature of sound is quite interesting as it doesn’t have any material constituents. Nobody was ever able to grab sound, to see sound or to taste sound. We cannot do any of those because a sound is a product of vibrations that spread through the air (or water) as acoustic waves. Depending on the properties displayed by the acoustic waves, the sound can be perceived differently. On the one hand, we can interpret a sound to have different levels of loudness which is attributed, in most parts, to the amplitude of the waves. The greater the amplitude (the height from the resting point to the top of the wave), the louder we recognize the sound to be. On the other hand, a sound can also have a different pitch depending on the specific period, frequency and wavelength it displays.

Acoustic waves generally follow the pattern dictated by sinusoidal functions, which we probably all encountered at some point in High School. For acoustic waves, the amplitude -determined by the height between the maximum and the x-axis- is still conserved. We only need one tiny adjustment; the x-axis now becomes known as the resting point. A period becomes the time it takes for the sound to complete its cycle. The frequency becomes the number of cycles completed within a specific time, which we typically calculate in Hertz (Hz; cycle/second). The wavelength is then the amount of distance sound can travel per period. They (all three) remain closely related to one another; the frequency is inversely proportional to both the period and the wavelength.

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These properties mean that the longer the wavelength (smaller Hz) is, the lower the frequency becomes. And as for the pitch, the inverse is also true. Although, there exist limitations to this observation. Namely, the limit of our human ear. They only possess the ability to detect sound within the range of 64 Hz to 23 kHz. However, some animals can perceive sound in much greater ranges than we can. Dogs are one of these animals with a hearing capacity between 67 Hz to 45 kHz. Nevertheless, cats take the lead here with their remarkable hearing sensibility ranging from 45 Hz to 67 kHz. This characteristic may describe their incredible success at hunting little prey such as rodents, which can emit sound as high as 100 kHz.

Depending on what the sound passes through, the speed and its direction can and will vary. Water, being thicker than air, will most definitely slow down sounds and redirect at a much greater angle than what we can observe with air. This redirection is also called refraction, which is the same phenomenon that is responsible for the shift of the image when seeing an object immersed in water. If, for whatever reason, you absolutely have no idea of what I am referring to, try this: take a transparent glass of water and partly submerged an opaque object in it (could be anything). You can see that the object seems broken when it passes through water, and that is refraction.

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Even though there are many properties characterizing sound, the ear is principally reactive to one, frequency. Amplitude will only play a background role to infer loudness to the sound. Our ear, which is our hearing organ, seems particularly attuned to pitch and loudness. As sounds are created, through the contact of objects causing vibration, it produces the acoustic waves as mentioned earlier. Upon hitting the auricle, the sound will be amplified and modulated before reaching the eardrum. The vibration, amplification and modulation create a chain reaction in the middle ear, which activates the ossicles (Malleus, Incus, and Stapes). The ossicles will then transmit the sound wave to the cochlea in the inner ear. In the cochlea, we can find plenty of hearing nerves, which connect to the brain. Once at the brain, the signal becomes interpreted to allow identification, classification and interpretation of the sounds.

It is the brain that is responsible for determining the pleasant nature of the sound we hear. Some people are affected by a condition that renders them unable to enjoy or derive any pleasure from music. This condition is known as musical anhedonia. It is a neurological condition caused by reduced connectivity in subcortical regions related to reward. Although these people might not be able to enjoy music, they can most definitely identify it, unlike those suffering from music agnosia. Despite their ability to hear, the latter cannot even tell the difference between music and noise. Individuals typically acquire this condition following an injury to at least one of the temporal lobes or after a unilateral stroke. These two conditions splendidly reveal the importance of the brain’s interpretation role in the perception of music.

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There is one more aspect of sound that I haven’t introduced yet: timbre. This term is often replaced by “sound quality” as it refers to the nature and distinctiveness of a sound, in other words, the pattern of harmonics. For instance, a violin will never sound exactly like a piano, even though you decide to play the same note at the same loudness level. Now, despite having described all these aspects and properties of sound, we still fall short when it comes to explaining where the pleasantness of music originates. However, what we have discussed so far was more related to sound itself and not music. What makes music is its rhythm or tempo, which creates sound arrangements through time, that can either be pleasing or not. When considering music perception, rhythm and pitch are the most central aspects involved.

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Now that I have introduced rhythm, we can start approaching closer to an answer. There are many factors involved; familiarity, distortion and reverb. As a general rule, we prefer sounds and/or patterns of sound that we are more familiar with; the ones we heard before. Usually, music acquires its different alluring attributes over relatively long periods. Music is pretty conservative as a general rule. However, beyond familiarity, there are distortion and reverb, each responsible for some aspect of pleasantness. Distortion comes from making the tone of the sound imperfect by changing its original form. Reverb is pretty much like echo, but instead of having the sound coming back to you in two parts, it comes back to you almost immediately. Although, not fast enough for merging with the original sound. The result becomes a continuation of the sound. We can often witness reverb in churches or even (ahem!) the shower. Reverb partly explains why it’s so delightful to hear ourselves signing in the shower. Yet, I cannot say I do much of that; my showers are always too short for that. How about you?

I thank you infinitely for reading this post and if you would like to know more about the mysteries that surround us, please join my subscription list to keep up with my newest content. If you have any questions, please add them to the comment section and I’ll make sure to answer as soon as humanly possible.

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Bring Up Tattoo—How it can be possible to mark our skin permanently

Not all appearance alterations are created equal; some may be more short-lived and others more permanent. If you think of tattoos, they mostly belong to the second category. So thinking carefully about certain aspects of the tattoo becomes imperative. Things like the symbolism or the artistry behind your new piece shouldn’t be random. Choosing a…

Bring Up Grad School—What Is the Reality Behind Higher Education

For people who want to pursue studies after completing high school, university studies may look very attractive. So, undergraduate studies may lead to graduate studies. However, undergraduate studies are not the same as graduate studies. The latter is not only more complicated, but it is also very different. First of all, contrary to your undergrad,…