01 From Practice to Theory
02 How does smell work?
03 The scent is in the air
04 Body Odor
05 Pheromones
06 Taste and Aroma
07 Trigeminal Nervous System
08 A true olfactory expert
09 The price of smell is made through training.
10 Smell in 3D
11 Loss of smell
12 Parkinson's disease and Alzheimer's disease
13 COVID-19 and Smell

Reviews

It consists of 13 chapters, and the beginning of each chapter briefly summarizes what you will learn in each chapter, and the end includes exercises that you can practice yourself.
Special terms are explained separately here and there.

Chapter 1, “From Practice to Theory,” describes memories of smell and what led to the study of smell.
An interesting episode is the rejection of certain foods that everyone experiences as a child.
This is the so-called 'neophobia'.
The author, who was very picky about food as a child, felt nauseated, especially when he saw green foods.
I didn't even want to taste it, and I didn't even put my mouth on it.
The peas I chose for my grandmother's funeral at my grandmother's house, which I visited once a week, were somewhat edible.
The author only began to taste them little by little when he was sixteen, and was even annoyed that he had only tasted asparagus or shiitake mushrooms when he was sixteen.
It's funny to hear that after becoming a college student, he tried to enjoy more of that kind of food, but couldn't because it was too expensive.
Neophobia is a state of fear of new things.
It is especially evident in the sense of smell.
Most children have a limited range of food choices because they initially perceive unfamiliar smells and flavors negatively.
The author suggests that to overcome neophobia, children need to perceive the smell and aroma about 10 times, and that children who are reluctant to eat any new food should at least try it out.

Chapter 2, “How Smell Works,” explains how the chemical senses of taste and smell work, unlike the physical senses of sight, hearing, and touch.
When you smell, a small amount of the odor's source enters your nose.
Then, the odor stimulus passes through 100 times more olfactory receptors than visual receptors and is processed in the limbic system, the brain area that controls emotions.
Fragrance, smell, and aromatic substances are all different, but 'fragrance' can be understood as a pleasant smell.
All scents are a kind of smell, but not all smells are scents.
These two expressions tell us about our cognitive state.
In contrast, an aromatic substance is a chemical component that is emitted to create the perception of a scent or smell.
Aromatic substances are substances that come into contact with olfactory receptors, and what we perceive at that time is scent or smell.

Chapter 3, “Scents Are in the Air,” explains why we find some smells pleasant and others unpleasant.
It also shows that the basic ingredients used in perfume making can smell terrible if left undiluted, and that our expectations play a significant role in our perception of smell.
Chapter 4, “Body Odor,” explains that body odor is as individual as a fingerprint and what influences body odor.
Individual body odor comes from special sweat glands in the areas of the armpits, anus, and genitals, called apocrine sweat glands.
While sweat glands on the back, face, and hands secrete slightly salty sweat to regulate body temperature and electrolyte levels, apocrine glands produce a cocktail of scented compounds that largely define your individual odor.
We all have a very unique body odor, and only identical twins have the same odor.
Also, the smell varies depending on the nutritional intake and can be influenced by ingredients such as curry and garlic.
All of these fragrance components are altered by the bacteria on our skin.
Therefore, the distinctive sweat odor is not due to the scent cocktail of the apocrine glands, but rather the result of bacterial decomposition.

In Chapter 5, “Pheromones,” we will learn what pheromones are, what their function is, which animal pheromones are famous, and whether human pheromones also exist.
Pheromones are released by one individual into the environment and picked up by a second individual of the same species.
Pheromones absorbed by the second entity evoke specific and typical reactions.
It could be a behavioral pattern or a physical development.
Pheromones can be said to be hormones that act not on one's own body but on other organisms of the same species.
Chapter 6, “Taste and Smell,” explores why taste and smell are easily confused, how aromatic substances travel from the mouth to the throat to the nose, and why, if your sense of smell is impaired, you may notice them, especially when you’re eating.

Chapter 7, “The Trigeminal Nervous System,” explains what the trigeminal nervous system is and how the chemical senses work together.
The trigeminal nerve is the fifth cranial nerve and is responsible for tactile perception of the skin and facial mucosa.
This is the so-called somatosensory system.
Some of the trigeminal nerve fibers not only have touch and pain receptors, but also TRP receptors, which originally sense temperature.
Most spices stimulate the trigeminal nervous system, and repeated exposure can alter sensitivity.
For example, if you are frequently exposed to spicy food, you become less sensitive to it and need to eat more peppers to get the same spicy effect.
The more frequently you are exposed to spicy food, the fewer receptors you have.
In the brain, interactions occur between the senses of smell, taste, and the trigeminal nervous system.
In all systems, incoming stimuli are processed in brain regions that take on a layered, overlapping pattern.
Therefore, these sensory systems influence each other.
Stimuli received from the trigeminal nervous system weaken the intensity of olfactory stimuli received at the same time, while olfactory stimuli strengthen the stimulation of the trigeminal nervous system received at the same time.

Chapter 8, “The True Smell Experts,” explores the abilities of dogs and rodents, known for their highly developed sense of smell, but also reveals that humans have a better sense of smell than they do at some odors.
Although humans have fewer olfactory receptors than mice or dogs, they are superior to these animals in other areas.
The area of ​​the brain that interprets smells is the prefrontal cortex, which belongs to the frontal lobe, and this part is much more developed in humans than in other species.
So, even if we receive less information from fewer olfactory receptors, we can perceive more.
We can translate olfactory information into language and interpret it in context.


Chapter 9, “Smell Mastery is Trained,” explains the special brains of olfactory experts and how the sense of smell can be trained, reminding us that training our sense of smell can also change our brains.
It is becoming increasingly clear that long-term training affects the brain.
However, there is still a popular belief that the brain's nerve cells cannot be renewed, and that the brain does not change any further after puberty, except in exceptional cases where it can change due to disease.
Today, it is known that even in adults, nerve cells can be replaced.
Although they are exceptions to the rule, new nerve cells can be created from old ones in three structures of the human body.
The first is the hippocampus in the temporal lobe, which is responsible for long-term and spatial memory.
The second is the olfactory bulb, which is where olfactory stimuli are first processed.
The third is the olfactory mucosa in the nose, where new olfactory receptors are constantly being created.

Chapter 10, “Smelling in 3D,” explores why our noses are associated with Gothic cathedrals, why dogs surpass us in smelling skills, and how our noses protect us from viruses and toxins.
Chapter 11, “Lost Smell,” explores the prevalence of olfactory disorders, their various causes, and treatments.
Some people have no sense of smell or only a slight sense of smell.
Approximately 5 percent of the population has anosmia, a condition in which they have no sense of smell at all.
15 percent have hyposmia, a condition in which the sense of smell is reduced.
Another form of olfactory disorder is parosmia, a condition in which a person perceives qualitatively different odors.
For example, sometimes all vanilla scents smell like burnt rubber.
Phantosmia is also a type of olfactory disorder.
At this time, it is important to confirm that the parties are not hallucinating.
In the case of false olfactory sensation or hallucination, there is no possibility of being mentally ill, it is only that you rarely smell good odors and that you smell the wrong odors, which is uncomfortable.

Chapter 12, “Parkinson’s and Alzheimer’s Diseases,” explores diseases that involve olfactory dysfunction and the introduction of olfactory testing for early diagnosis.
There is a clear early sign common to both diseases: loss of smell.
More than 90 percent of people with Parkinson's and Alzheimer's disease have problems with their sense of smell.
Not only Parkinson's disease but also Alzheimer's disease can cause significant olfactory impairment.
This is a much more serious level than the natural decline in olfactory ability that occurs with age.
What's interesting here is that the loss of smell appears earlier than the typical symptoms of both diseases.
People with Parkinson's and Alzheimer's disease have reported experiencing loss of smell decades or more before they were diagnosed.
But I didn't attach any special meaning to it.
But in the future, this loss of smell could become very important.
Chapter 13, “COVID-19 and Smell,” explores how the coronavirus that has swept the globe in recent years has impaired our sense of smell and how we can train our sense of smell to enhance it after COVID-19.