In a magical scene towards the end of the film Ratatouille in 2007, the food critic notoriously hard, Anton Ego, is instantly transported in time, his childhood memories revived by a tablespoon of the homonymous dish of the film. No photos were needed, only the taste and aroma of food.
The smell is the quietest of our senses, but also one of the most powerful. In fact, you can even open the gates to the memories that we think forgot a lot.
It is also the most personal and subjective sense, which is what makes it so difficult for people according to what smells good. However, there seems to be a consensus on the worst smell of the world.
In 1889, in a German laboratory, a chemical reaction that involves a compound called Tioacetona produced such a terrible stench that caused people to vomit and faint a half kilometer away, forcing the partial evacuation of the city of Freiburg. We still don't know what exact reaction this stench caused, but it seems that nobody is in a hurry to find out.
But what happens when our smell begins to fail? What if the smell of losing was more than a simple symptom?
A shortcut to our emotions
The smell is an evolutionary advantage: it warns us of invisible dangers and puts us on alert. The aroma can also influence our decisions, and the big brands are aware of this, perfume their stores with fragrances that take advantage of our emotions and invite us to stay.
Odors have the ability to awaken intense memories and emotions, and the olfactory bulb is responsible for this. This small area of the prosentephalon, located very close to the nose, receives olfactory signals and sends them directly to the areas of the brain that handle our memory and emotions.
Despite its importance, the smell remains the least understood of the senses, it is often underestimated. When it fades, it usually goes unnoticed, but we may not realize how important it is until we lose it.
This is what happened to Michele Crippa, a recognized “Italian super taster” who lost his sense of smell during the pandemic. Although he recovered it weeks later, his personal nightmare had just begun, since when his sense of smell returned, he was distorted. The oranges smelled of burned plastic, the peaches smelled of basil and vanilla made him feel ill. This was likely because neurons in their olfactory bulb had been damaged.
While any loss of smell is unpleasant, it could have a greater meaning: a warning signal of the deep with our brains.
A common cold or Parkinson's?
Most of us have lost our sense of smell at some point, generally thanks to a simple episode of cold or flu. However, this symptom can also be an early symptom of neurodegenerative diseases such as Alzheimer or Parkinson. This has been known for some time, but the surprising thing is that the loss of smell occurs years before the symptoms of these diseases appear.
So, could the smell loss be used to predict Parkinson's disease? The answer, useless, is, is: it depends.
An early warning
One of the main problems with neurodegenerative diseases is that the damage is already very advanced for the moment they can be diagnosed. In the case of Parkinson's disease, when the first symptoms appear (stiffness, tremors, etc.), more than half of the neurons that produce dopamine, the neurotransmitter that controls the movement, have already been lost.
The identification of the first symptoms such as the loss of smell, which affects up to 90% of patients, could serve as a biomarker, alerting us about the presence of the disease. This would allow us to diagnose it much earlier and provide access to more effective treatments.
The problem is that this symptom is not exclusive to Parkinson's: it can also appear with aging, stress or other conditions. This means that we tend to minimize its importance.
About the author
Jannette Rodríguez Pallares, Professor of Human Anatomy and Embryology, University of Santiago de Compostela.
This article is published again from the conversation under a Creative Commons license. Read the original article.
We still do not know certainly why neurodegenerative diseases cause smell loss, although we have some clues. In some Parkinson patients, the disease can begin in the olfactory bulb long before spreading to the areas that control the movement. This is because certain viruses, pesticides or toxins that we inhale could damage it and cause alterations to the area.
In the case of Alzheimer's disease, the damage could begin in a small bluish region of the brain stem called Locus Coeruleus, as a recent study has revealed. This “alert button” keeps us awake and focused, and its connection with the olfactory bulb is what links them smells of emotions. When that connection breaks, the problems occur with the smell long before the first signs of dementia arise.
In summary, the loss of the ability to smell would not be a symptom of the disease itself, but rather a warning sign that the degenerative process has begun.
Diagnosis through smell
When a patient enters the clinic, it is not always easy to distinguish between Parkinson's disease and other similar movement disorders. A loss of smell, combined with other tests and indicators, could help confirm the diagnosis. It could also help us predict the progression of the disease, since it is related to more serious forms of the disease.
In addition, the loss of smell in Parkinson's disease is selective. Patients perceive pleasant odors such as chocolate without problems, but have difficulty detecting neutral or unpleasant odors such as soap, smoke or rubber.
Other patients, especially women, experience something even more strange: olfactory hallucinations. This means that “ghost” smells perceive, such as tobacco or burning wood, which are not really there.
Incredible, although it seems, Parkinson's disease even has its own aroma, which has been described as woody and musk. We know this thanks to Joy Milne, a Scottish woman with a greater sense of smell: she was able to recognize this particular smell of her husband 12 years before the disease was diagnosed.
The loss of smell may seem somewhat confined in the nose, but in reality it is a window to the brain. It allows researchers to take a look at the brain to decipher their secrets and gather valuable information to help us take care and improve the quality of life of those who suffer from neurodegenerative diseases.
