Why can smells trigger strong memories?

Why is it that when you smell a certain flower fragrance, a certain brand of perfume, or the smell of burning firewood in the distance, a lot of memories and emotions will flood in, as if you had experienced a trip back to the past?

Our brains are strange. Compared with sight, hearing, taste and touch, smell is more closely related to memory. Humans have about 400 odor receptors and can recognize trillions of different odors. Although scientists have not yet solved the details of nerve responses to various smells, there is evidence that smells have a great influence on the brain's memory of the past.

From molecules to mucous membranes

When your nose inhales molecules in the air and smells something. These molecules will roam in your olfactory system. First, they will attach to the nasal cilia in the nasal cavity and then dissolve in a layer of mucosa. At this time, 654.38+02 million receptors attached to nasal cilia produce nerve impulses.

The length of nasal cilia is 1- 10 micron, and the width is less than 1 micron.

Nerve signals are transmitted along thousands of nerve fibers to the olfactory bulb in the frontal lobe of the brain, where they are processed. At the same time, the process of detecting odor will evoke memories in deep areas of the brain.

Hippocampal junction

When the neural signal is processed, the information will continue to be transmitted to other parts of the brain near the olfactory bulb, especially the limbic system, which is mainly responsible for controlling the most primitive parts of the brain, including memory, emotion and behavior.

The "hippocampus" shaped like the hippocampus is a part of the limbic system of the brain. In fact, the hippocampus is located next to the olfactory bulb and is mainly responsible for the storage, transformation and orientation of memory.

When the smell is first smelled and processed, the brain sends messages to the hippocampus and other components of the limbic system to associate the smell with people, things, places or events. Therefore, when you smell the same smell for the second time, you can recall your first memory.

As far as olfactory memory is concerned, the peak of memory formation is about five years old. This explains why this smell will trigger many people's childhood memories.

A deeper feeling

Smell is different from the other four senses because it bypasses the thalamus between the cerebral cortex and the midbrain and enters the brain in a more direct way. Information collected by vision and hearing must pass through the thalamus. It can be seen that vision and hearing have less influence on the brain than smell.

The transmission of odor is directly processed by olfactory bulb, which does not involve other structures, which not only explains why odor can trigger such a strong memory, but also seems to explain why odor is difficult to describe in words.

Zhu Xiang in the pencil box in the 1980s and 1990s.

Research shows that people can only recognize the smell of less than half of the objects, even what they touch or experience every day. Unless, of course, there are words or pictures.

Those life experiences, people I have met, things I have experienced and places I have been to all contain deeper feelings, situations and memories. These subtle connections are even more complicated than the language itself.

I don't know if you have ever had such an experience, because the appearance of a smell will bring the past to mind, which makes people feel sad.

Smell is so capricious that it often inadvertently triggers our memory of a thing or a person, which is often accompanied by rich and touching emotional experiences.

So how does the sense of smell do this? Maybe we can find some clues from the structural characteristics of the olfactory system.

1 olfactory system

From the perspective of neuroanatomy, the olfactory system is highly coincident with the limbic system responsible for emotion and memory coding. After the odor molecules in the air enter the nasal cavity, they combine with the olfactory receptors on the olfactory mucosa, induce nerve electrical impulses of olfactory sensory neurons, and then transmit olfactory information to the olfactory bulb. Many structures of limbic system are directly or indirectly projected by olfactory bulb.

The amygdala, orbitofrontal cortex and hippocampus are specifically mentioned here.

The amygdala is closely related to emotional response and emotional memory, and it receives direct projection from olfactory bulb. So the shortest information from olfactory receptor neurons to amygdala only needs to span two synapses.

The orbitofrontal cortex and hippocampus receive secondary olfactory projections, and they are only three synapses away from olfactory receptor neurons. Among them, the orbitofrontal cortex is located in the ventral part of the prefrontal lobe and plays an important role in complex brain functions such as smell, emotional regulation, learning and behavioral decision-making. It's also related to personality: a railway worker named phineas gage's personality has changed obviously because of orbital frontal cortex injury.

At first glance, it is a brother with a story.

The hippocampus, the structure in the temporal lobe, is inextricably linked with our memory. It is responsible for various forms of memory, in which situational memory can help us travel in time and relive the events we have experienced. The hippocampus is also responsible for consolidating the contents of short-term memory and making it enter long-term memory. In Alzheimer's disease (Alzheimer's disease), the hippocampus is one of the first brain structures to be damaged, so the early manifestations of Alzheimer's disease include short-term memory impairment and disorientation. Patients often can't remember things and get lost on the road.

Inadvertently awaken autobiographical memory

This anatomical advantage of the olfactory system makes smell a natural trigger for emotional memory. Of course, the triggering effect of odor also needs the individual's contact and experience with odor and its situation in life. Proust, a French novelist, has this description in Memories of the Past:

"The sky is gloomy, and it seems that it will not clear up the next day. I was depressed, so I broke off a small piece of Madeleine and dipped it in tea, and subconsciously scooped up a spoonful of tea and sent it to my mouth. But just as this spoonful of hot tea mixed with a little heart crumbs touched my palate, I suddenly shuddered and noticed that strange changes were taking place in myself. I feel a wonderful pleasure, which is helpless and sudden, and the reason is incomprehensible. "

It turned out that the smell of little Madeleine's dim sum soaked in tea was often smelled by the author when he visited the menstrual family when he was a child. It is this that activates the author's memory of the past, followed by a warm and pleasant experience in the situation at that time.

The above example contains at least three important messages.

First, the experience of olfactory awakening usually belongs to autobiographical memory, with strong emotional experience, which often involves those events and experiences originally associated with smell;

Second, the memory of smell can last for a long time, which is most easily formed in childhood and can last for decades or even a lifetime;

Third, the relationship between smell and memory events does not need to be consciously perceived by individuals. In fact, smell often works inadvertently.

3 empirical research

Previous studies have provided an empirical basis for the above viewpoints.

1) First of all, autobiographical memory is indeed the most relevant memory form with smell.

Autobiographical memory refers to the overall memory of personal life events and scenes and accompanying self-experience.

For example, in the research of Chu He (2002), the subjects recalled the experience of a certain period of time according to a smell name; Later, when they touch the smell label, they further recall the smell corresponding to or unrelated to the label, or visual stimuli; Finally, they need to grade the emotional experience they just recalled and write down the content of the memories.

The results show that the subjects who smell the corresponding smell not only have stronger emotional experience, but also describe the recalled events in more detail. This makes the clue effect of smell on autobiographical memory verified by experiments.

In real life, because of the close relationship, in the events experienced by both sides, there is often the smell of the other side, which will be firmly remembered by you. Once this smell appears in later life, the past will reappear as time goes back.

2) The researchers also found that in the long-term memory of the sense of smell, the connection between a certain smell and the things that were initially bound is stronger and closer than that between it and the things that were later bound.

In the experiment of Yeshurun et al. (2009), the subjects first learned the relationship between positive and negative olfactory/auditory stimuli (such as the smell of peaches and stinky fish/guitars and harsh sounds) and neutral visual pictures. In the test conducted a week later, the negative olfactory and auditory stimuli related to the picture showed the first causal effect, that is, the first negative stimulus was more closely related to the picture.

Interestingly, in the MRI scan, when the subjects saw the picture, compared with the smell-bound picture, the sound could significantly activate the hippocampus at first, which directly predicted the associative memory of the subjects when they were retested eight days later. This fully reflects that the odor memory formed in the early stage will be more closely related to the corresponding scene.

Looking back on our life experiences, the impression of a particular smell always stays in the scene where we first came into contact with it. Even in the later experience, smelling the same smell again in different scenes is often the first event to win the final victory in this contest between old and new memories dominated by smell.

3) The persistence of olfactory memory has also been confirmed by related studies.

Willander and Larsson(2006) recruited some subjects aged 60 to 80 and asked them to recall relevant autobiographical memories according to real smells or text clues. The results show that smell can remind people of their childhood (6- 10 years old) more than text clues.

Haller et al. (1999) also found in the experiment about 28 years later that adding vanilla to artificially fed infant milk powder will make these infants prefer tomato sauce mixed with vanilla than breast-fed people.

These studies show that the long-term memory of smells is very lasting, even for life, and often shows our preference for specific smells.

Many people will be surprised that when the smell triggers memory, "the reason is incomprehensible." In fact, it is a common phenomenon that odor affects behavior "for no reason". For example, when the smell of oranges or lavender is used as the background smell in a dental clinic, patients waiting for treatment will involuntarily reduce their anxiety level.

In laboratory research, the odor during sleep can regulate memory connection and affect the behavior of individuals when they are awake, and emotional stimulation and connection are often more effective in this process. It can be seen that although the connection between the smell and the past situation and the ta has been out of your consciousness, this connection is still strong enough to bring you unexpected surprises.

Maybe one day, at a casual moment, a familiar smell of t a will make you remember the past, just like Proust's little Madeleine cookies, bringing you a vivid beginning and end, a sad sigh; One day, you will begin to miss the taste of ta, or the taste of things related to ta. Whether it is a relative or a lover, past memories will be involved through a trace of smell, which makes people feel worried and mixed feelings.

First of all, let's talk about the psychological definition of memory: memory is an ability to store and extract information. From the perspective of cognitive psychology, memory is an information processing process, including coding, storage and extraction.

For example, if you see a string of phone numbers, write them down through meditation or association with the meaning of the numbers. This is called coding, and then store them in your mind. This is called storage. When you need to input this string of numbers with your mobile phone to make a phone call, this is called extraction. This process is actually comparing the human brain to a computer. We can store a lot of information on the computer, and then input keywords to search when necessary.

Triggered memory is actually the process of extracting information in the process of memory. Memory retrieval is influenced by many factors, one of which is related to our coding background. Psychologists have discovered this feature and the principle of coding specificity.

For example, Xiao Ming is a senior three student who has to recite English words at eight o'clock every day. Xiao Ming's mother has a habit of bringing apples to Xiao Ming at this time every day, so when Xiao Ming recites English words, they are accompanied by the smell of apples. According to the principle of coding specificity, when Xiao Ming later recalls these words, if there is still the smell of apples around him, then the words he recalls are much better than those without apples.

Isn't it amazing? Smell will affect people's memory! Maybe you can try next time.

There is another well-known example: we met someone on a certain occasion, and then in another place, we felt deja vu, but we couldn't remember where we met. Why? Because this violates the principle of coding specificity, the coding background is inconsistent with the extracted information, that is, it can't be remembered in another place!

There are many researches on memory in psychology. If you are interested, you can learn about it ~

When you smell the school fried string, pumpkin pie and osmanthus moon cake, you suddenly immerse yourself in a series of vivid memories of that year. What smell can trigger such a strong and real memory, and feel that time has gone back to childhood?

It is called "autobiographical memory of smell" or Proust phenomenon. In fact, research shows that smells are particularly effective in reminding past experiences, which is more effective than clues from other senses (such as vision or sound).

One of the reasons may be related to the way the brain processes smells and memories. Smell is transmitted through your olfactory bulb, which is the odor analysis area in your brain. It is closely connected with your amygdala and hippocampus (the brain area that processes memory and emotions).

This close connection can explain why smells are associated with vivid memories in the brain, and then when you come into contact with this special smell trigger, memories will flood again. As Psychology Today points out:

"Interestingly, visual, auditory (sound) and tactile (tactile) information does not pass through these brain regions. This may be why the sense of smell can trigger emotions and memories more successfully than any other senses. "

Before reaching your thalamus, smells first pass through other areas of your brain, including areas that control memory and emotions. Therefore, you have all these extra treatments for smells, even before you realize them.

Your body also contains at least 1000 olfactory receptors (such as vision (4) and touch (at least 4)) than other senses, which means that you can distinguish different types of smells, even those that you may not be able to describe.

Taken together, this makes the memory of smell clues particularly fresh, which is different from other memories. For example, in a study for the elderly, participants were given three types of prompts (words, pictures or smells) and asked to recall the memories triggered by these prompts.

It is found that those memories prompted by smells are often old memories of the first ten years of life, while those related to speech and visual information come from early adulthood.

Olfactory-induced memory is also related to "strong feeling brought back in time", which is "less frequent" than other clues.

Another study also shows that when it comes to smell, older people can recall more than twice as many memories as young people. According to the researchers, the elderly have obvious and complete olfactory memory.

Different smells will not only bring positive associations and memories. For example, odor is known to induce physiological awakening and trigger flashbacks related to trauma.

They are also thought to have played a role in triggering uneasy memories in patients with post-traumatic stress disorder (PTSD). Interestingly, a mother's fear can even be transmitted to her children through the smell. In one study, female rats were afraid of the smell of mint before pregnancy. Later, the young mice were exposed to the smell of mint and showed the same fear as the mother mice.

Newborn puppies learned to be afraid of the smell when their mother was away, but they didn't learn to be afraid of the smell of mint when their amygdala was blocked.

Therefore, it seems that babies can learn about potential environmental threats from their mothers through smells, and their sensory and motor development allows them to fully explore the surrounding environment.

Smell has such a great influence on fear that some mice try to block the pipe to prevent the smell from entering. The researchers plan to study this habit further.

Autobiographical memories evoked by smells usually happen by accident. You happened to take a breath when an uninvited smell passed through your nose. However, you can use the power of smell to trigger real physical and emotional reactions through aromatherapy. For example, research shows that:

Of course, anxiety is only one use of aromatherapy. Other potential uses are varied, including:

If you still have a keen sense of smell, you are lucky, because smell is closely related to many different physiological processes. Researchers at the University of Chicago, using data from a national representative sample of more than 3,000 elderly Americans, found that those who can't perceive smells (called smells) are more likely to die within five years.

Specifically, in the first olfactory test (including identifying five common odors), 39% of the participants will die in the next five years, while the proportion of participants with moderate olfactory loss and healthy subjects is 19%.

The loss of sense of smell is a very strong indicator close to death, even exceeding the known main cause of death, and has nothing to do with known risk factors (such as nutrition, cognitive function, mental health, smoking, alcoholism or weakness). Olfactory loss is a more powerful predictor of death than cancer, heart failure or lung disease diagnosis.

The researchers said that the loss of olfactory function may not be the cause of death, but it may "become a weather vane to slow down cell regeneration or a sign of cumulative toxic environmental exposure". As the Guardian reported:

"The top of the olfactory nerve, including the olfactory receptor, is the only part of the human nervous system that is continuously regenerated by stem cells.

The production of new olfactory cells will decline with age, which is related to the gradual decline of our ability to detect and distinguish odors. The loss of sense of smell may indicate that the body is in disrepair and cannot repair itself. Olfactory nerve is also the only part of the nervous system exposed to the outdoors. Therefore, it provides a fast passage for poisons and pathogens to enter the brain, so losing the smell may be an early warning that eventually leads to death. "

If you miss the old memories of your childhood, because your sense of smell is no longer what you used to feel, you can take some measures to improve it. First, check whether there is zinc deficiency. Zinc is an essential trace mineral to produce carbonic anhydrase VI(CA-VI), which is very important for taste and smell. This is why olfactory loss is one of the typical symptoms of chronic zinc deficiency.

Mild zinc deficiency is more common, especially in infants, pregnant or lactating women, the elderly, patients with gastrointestinal malabsorption or intestinal diseases, and vegetarians. Good sources of dietary zinc include meat, oysters and wild fish, raw milk, raw cheese, beans and yogurt.

If you are healthy and have a balanced diet, you seldom need to supplement zinc to meet your body's demand for zinc. You should try to get zinc from your diet.

Next, try to remember these tips that can enhance your sense of smell:

Because this nerve is particularly sensitive. People often say, is there something wrong with your nerves? Is this the tendon you said?

The sense of smell has a unique ability to unlock vivid and emotional memories that have been forgotten before. Smell can evoke our emotional memories of the past. Smell can affect our daily life and regulate our subjective emotions at the subconscious level.

Think of Winnie Sheen's Taste;

I miss your smile, your coat, your white socks and your smell. ...

Most of us have had this experience, because of the appearance of a smell, bits and pieces of the past will come to our hearts and make people feel sad. Smell is like this, which often inadvertently triggers our memory of a thing or a person. Such memories are often accompanied by rich and touching emotional experiences.

The taste of the country and hometown reminds us of childhood, and the taste of wine reminds us of the taste of youth. When people reach middle age, they have a strong homesickness, which reminds people of all familiar smells.

There should not be all smells here, but some special smells or smells that cause feelings. When your feelings erupt, you just touch some special smells, then these smells will definitely make you linger!

This is because the unique structure of olfactory nerve can directly link the memory module of the brain.

The smell won't make you forget! Durian, stinky tofu, and poop