How a person's memory works is just about complicated. How does human memory work?

Scientists try to improve human memory with electrical impulses

All the information that is stored “in the head” is taken for granted by us. However, in fact, the mechanism of memory is so complex that scientists fail to fully understand it. Nevertheless, new discoveries are made almost every year.

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A total of 200 electrodes were implanted into the brains of more than twenty patients with epilepsy (they are the most commonly observed memory disorders), scientists at the University of Pennsylvania implanted a total of 200 electrodes. Then they began to stimulate the centers responsible for memory with electrical impulses. At the same time, each electrode also worked in the recording mode, registering up to a thousand indicators per second. This helped not only to track the process, but also to develop an individual “treatment” algorithm for each patient. The result - memorization improved by 15%. While scientists are at the very beginning of the path. The ultimate goal is to develop a device that can be conditionally called a “brain pacemaker”. Why not?

Everyone's different

Memory is the ability to store information and also reproduce it. It is inherent in all creatures that have a nervous system, but each species has its own nuances. For example, coelenterates - jellyfish and ctenophores - have only simple summation (short-term) reflexes. In arthropods, memory is a ready-made program of reactions to environmental conditions. Cephalopods, birds and mammals already have quite decent memory abilities. But people are endowed with the most perfect memory mechanism. Moreover, it is “tied” to individual characteristics. For example, already in childhood it can be said whether the child's memorization of images, associative or abstract memory predominates. In this case, often the shortcomings of one type of memory can be compensated for by others.

So nervous...

The brain contains 86 billion nerve cells that send impulses through special contacts - synapses. Japanese scientists introduced the smallest light particles into the human brain and filmed the process on video. The more intense the work of thought (for example, when solving mathematical problems), the more active the neurons became. They moved faster and faster in a continuous stream, somewhat reminiscent of amoebas (a genus of microscopic unicellular protozoa). It turns out that the well-known expression “move your brains” has a direct meaning.

Memory itself can be divided into several types. The first is immediate, which lasts a few seconds. Usually you walk down the street, look around and immediately forget what you saw, right? Short-term memory allows us to remember something for several hours. But if the information is extremely useful, it goes into a long-term form of memory, where it is stored from several days to a lifetime.

Thought Giant

Long-term memory is formed approximately 5-8 hours after the receipt of important information. In this case, proteins with a special molecular structure are formed, and a separate neural network arises. When it is necessary to remember something, the material “recorded” at different points in the chain is called up and then it is formed into a meaningful plot.

The number of neural connections increases in the process of growing up. So, a small child has neurons, but there are practically no connections between them. They begin to appear only in the process of knowing the world around us. If we compare the human brain with a computer, it could store up to 7 million megabytes. There are a lot, but not a single person in history is known who would actually reach such heights of intelligence (this is about how to memorize all the books available in the National Library).

With age, natural changes occur in the brain - the number of nerve cells decreases, connections weaken. You can delay this time. It all starts with proper sleep and nutrition. For example, food poor in proteins and vitamins reduces the ability of memory. And the inclusion in the diet of foods rich in magnesium, calcium and glutamic acid, on the contrary, improves it. Poor effect on memory and inactive lifestyle. And, on the contrary, she “likes” a change of impressions, communication with people, outdoor activities and sports. So it turns out that running can run away not only from a heart attack, but also from sclerosis.

CURIOUS

The American Kim Peak, the prototype of the protagonist of the film “Rain Man”, had a phenomenal memory. He memorized 98% of all the information he read, and he could simultaneously read the right page with his right eye, and with his left eye the left one in the spread of the book. But Kim was born with a craniocerebral hernia, damage to the cerebellum and the absence of the corpus callosum (the department that connects the hemispheres of the brain). It is clear that such things do not lead to giftedness. However, as the scientists found out, the case of Kim Peak is unique - due to the absence of the corpus callosum, neurons created new connections, which led to a multiple increase in memory precisely due to pathological structures.

COMPETENT

Vladimir Kulchitsky, Academician, Deputy Director for Research at the Institute of Physiology of the National Academy of Sciences:

Scientific studies confirm that proper sleep is necessary for the normal functioning of the brain and especially the human memory mechanisms. After all, contrary to popular belief about sleep as a serene peace, this is just one of the most active states of our brain. There are many examples (in particular, Dmitry Mendeleev with his periodic table) when it was in a dream that scientists came up with the ideas of scientific discoveries. Salvador Dali fell asleep sitting, holding a heavy key in his hand. As soon as his grip loosened while falling asleep, the key slipped out and woke him with a roar. The artist believed that this helps him draw new thoughts and ideas for paintings from the borderline state between sleep and wakefulness. And how many legends about prophetic dreams exist!

Have you ever wondered why small children under the age of three sleep so much? The fact is that in the first years of life, such a stream of various information and impressions falls upon the child that the brain needs time to process it. In order for short-term memory to turn into long-term memory, new interneuronal contacts must be formed, and their formation is best done during the “sleepy activity” of nerve cells. If we state the process in simple terms, then there is a systematization (as if “sorting out on the shelves”) of everything that happened to us during the period of wakefulness. “Conducts” this part of the brain called the hippocampus. It is he who is responsible for ensuring that the information is not only sent to a specific address, but also “archived” in the relevant departments. So, in case of non-observance of the optimal daily regimen (and normally, the average person should sleep for at least seven hours), these processes are violated, failures occur. And since errors tend to accumulate, this negatively affects the mechanisms of memory in general, and often on human health.

However, there are examples of prominent personalities who supposedly needed very little time to sleep. For example, it is believed that Napoleon Bonaparte slept no more than four hours. However, it seems to me that these statements are only partly true. Indeed, for some time a person can (due to life circumstances) exist in an extreme rhythm. But it is impossible to live like this all the time - the brain simply cannot withstand the overload. Observations show that such people (for all their genius) live much less than others. And, as a rule, they are distinguished by an unstable psyche. By the way, scientific articles have appeared on the relationship between lack of sleep and the incidence of Alzheimer's disease.

And vice versa, observations of centenarians show that they all eat right, observe the daily routine and lead an active lifestyle.

human memory extremely economical. If it retained all the irritating factors and all the information, all the daily little things, then most likely the brain would explode or, due to excessive exposure to stimuli, we would become incapacitated.

The brain differentiates and selects new information in order to be able to work more efficiently. And this choice the brain of each person makes individually. Memory retains only those things to which we attach special importance and which we consciously and emotionally process. Thus, feelings play a significant role in the process of storing information in memory.. The so-called limbic system is responsible for this, which, according to the structure of the brain, is located directly under the cerebral cortex. The limbic system, the center of the senses and the brain, also includes the “new detector” hippocampus, which evaluates incoming information from an emotional point of view. No new information relating to any facts or biographical memories enters long-term memory without passing through the limbic system, which serves as a filter, looking for only the necessary information, associates it with feelings, and then distributes it to the cerebral cortex. The more often this process occurs, the stronger it is emotionally colored, the faster this information will be learned and the longer it will be stored in memory.

The novelty, meaning, and intensity of emotional coloring are decisive factors in what we retain in our memory. Strong emotional events are processed differently than minor ones, extraneous facts are perceived worse than personal experience. Neutral information, such as ordinary school material, must be processed consciously, repeated, transformed, supplemented and simply memorized. The principle applies First in last out“, meaning: what a person learned first is remembered best. Fresh information only after a conscious explanation can be stored for a long time in memory.

Thus, the expression "to transfer knowledge" is erroneous. Knowledge cannot be fully transferred, but must be built into the memory of each person through his own system of nerve connections. Goethe said a wonderful phrase: "You need to get your knowledge in order to possess it!".

Just because our brain is very economical and has many filters, however, does not mean that our large storage, our long-term memory, can ever be full. The cerebral cortex has an incomprehensibly large amount of memory. And the more we saturate it, the faster and better our brain can think and remember new information.

My daughter went to first grade and was faced with the fact that the rules had to be memorized. It was very difficult for her at first. Even if she could repeat the entire text in the first hour after memorization, then some of the information was lost later. And I remembered these rules by heart from school.

Then my little genius asked a completely logical and wise question: “Why can’t I remember the rule that I learned today, and you still know it?”. I was in no hurry to answer - I decided to study the theory and compare it with life experience.

I started my research from the basics. What is memory? Where is human memory stored? What is the structure of memory?

By definition, it is a thought process consisting of the following components: memorization, storage, reproduction and forgetting.

How does memory work? It is formed throughout life and stores our life experience. Physically, the process can be described by the emergence of new connections between a huge number of brain neurons.

The processes in the brain are not fully understood, and scientists continue research in this area of ​​the human body.

The location of human memory is still debated. To date, it has been proven that the following areas of the brain are responsible for this part of consciousness: the subcortical hippocampus, hypothalamus, thalamus, and cerebral cortex.

The main storage sites are the hippocampus and the cortex. The hippocampus is located in the temporal lobe on both sides of the brain. To the question of which hemisphere is responsible for memory, we can safely answer that both, only the right lobe “controls” factual and linguistic data, and the left lobe controls the chronology of life events.

The appearance of neural connections is due to the work of the receptors of the sense organs: vision, taste, smell, touch and hearing. The brain captures all the electrical impulses from them, and the brightest moments that cause strong emotions (for example, first love) are remembered better.

Thus, human emotions affect memory.

In each person, the predominance of a memory property through any sense organ is possible.

For example, some learn the text well from the textbook when reading, others are better off hearing the text from another person, others have an excellent memory for smells, and so on.

Various external and internal factors affect the "quality" of our memory. There are many reasons that cause violations of this process.

Internal causes include incorrect handling of information in the following areas:

• memorization - so that the information is not forgotten, you need to work with it;
• interference - a large number of new information leads to forgetting important previously acquired information;
• repression - negative memories are forgotten faster;
• distortion - the memorization and reproduction of information occurs against the background of our feelings and emotions, therefore such processing makes the data subjective;
• storage and reproduction errors - if the data is remembered with errors or inaccuracies, or not completely, then their reproduction will be incorrect.

External reasons are also enough:

1. Genetic disorders (for example, autism).
2. Hormonal disorders (including diabetes mellitus, thyroid pathology).
3. Depressive or stressful conditions and diseases (neurosis, schizophrenia).
4. Exhaustion of the body caused by overwork, insomnia, illness, poor diet, alcoholism, smoking, taking certain drugs (for example, benzodiazepines).
5. Age-related changes (Alzheimer's disease).

Especially detrimental, in addition to diseases and injuries, alcohol addiction affects memory. It is known that even a single use of alcohol leads to disorders, and in alcoholism there is a destruction of neural connections in the hippocampus, a violation of cerebral circulation, and the occurrence of beriberi.

All this leads to a loss of the ability to assimilate new information.

Acute conditions such as stroke and heart attack can also cause the destruction of neural connections, and the consequences can be enormous, and recovery takes a lot of time, effort and patience. Sometimes all attempts are unsuccessful.

The hippocampus contains a substance - acetylcholine - responsible for the transmission of impulses from one neuron to another. Its deficiency causes memory impairment. This phenomenon is especially observed in old age and causes Alzheimer's disease.

Structure

A long study of how human memory works led to the creation of a detailed classification. One of the criteria is the duration of information storage. According to it, the following types of memory can be distinguished:

• instant (touch);
• short-term;
• operational;
• long-term.

Instantaneous is characterized by the fact that information is fixed by the receptors of the sense organs, but cannot be processed. It, in turn, is divided into iconic (visual perception) and echoic (auditory perception).

An example of an iconic view - you see a banner with an advertisement and a phone number on the street, in a second you will not remember this number. The echoic view can also be seen on advertising, but you did not see the phone number, but heard it on the radio. Instant memory allows you to store information up to 5 seconds.

Short-term is the consequence of a single perception and immediate reproduction. If we take an example with the rule for the first grade, when the daughter reads it syllable by syllable once without repetition. She will be able to keep the rule in memory for a period of time from 5 seconds to one minute.

The hippocampus is responsible for short-term memory. The evidence is the fact that when the hippocampus is damaged (during surgery, for example), a person immediately forgets the event that just happened to him, but remembers the information accumulated before the damage.

Working memory is the same as short-term memory, but information is stored only within the period of its use. For example, the daughter read the rule and used it to complete the exercise from homework, and then forgot.

This type allows a person to quickly solve a problem here and now and forget later unnecessary information.

Long-term stored in the cerebral cortex. It develops simultaneously with the short-term and is its consequence. After repeated memorization and application of information that is within short-term memory, it is fixed in the brain, namely in the cerebral cortex, for a long time or even for life.

This is an example where a rule learned in first grade and applied throughout 11 years of schooling is remembered forever. Long-term memory requires the participation of all resources of consciousness: mental, sensual and intellectual.

Only conscious and fully meaningful information can take a place in a person's long-term memory.

The structure of memory is simplified as follows: memorization - storage - reproduction. When memorizing, new neural connections are built.

Thanks to these connections, we remember (reproduce) information. Memories can be extracted from long-term memory on their own or under the influence of stimuli on certain parts of the brain (for example, hypnosis).

The duration of information storage is affected by a person's attention to the latter. The more attention is focused, the longer the information will be stored.

Forgetting is also an integral part of memory. This process is necessary to unload the central nervous system from unnecessary memories.

Conclusion

Now I can answer my daughter's question:

1. Memory is a process of several separate components. To memorize information, you need to comprehend it, repeat it many times and periodically apply it in practice. This is due to certain properties of the brain and, accordingly, the existence of several types of memory.
2. It is important to know where the memory is stored in order to understand what the memorization of the rule depends on. It is found in the brain with a large number of neurons. To fix information in the cerebral cortex, it is necessary to create strong neural connections.
3. Knowing how memory works will help develop it, and enjoy this process.

This part of the consciousness is connected with the senses, so you can observe how the text is better remembered: when reading or by ear.

The process of memorization is also connected with the intellect: the more and better we learn, the easier memorization will be given later.

Successful memorization is associated with the mental state of a person: a depressed mood can interfere with the process; the more positive emotions, interest a person shows in information, the more carefully he studies it, and the better he remembers it.

That is, it is important to have positive attitude. For children, you can create conditions for the game to attract attention.

The need for development

The device of human memory suggests a relationship with intelligence. By developing it, we develop the intellect.

A person who devotes a lot of time to memorization and comprehension becomes more attentive and organized, he develops all kinds of thinking, imagination and Creative skills. In addition, such brain training prevents age-related diseases associated with memory impairment.

Depending on the goals of memorization training, there are three areas of use:

1. Household direction - necessary to eliminate forgetfulness at the household level (for example, periodically forgetting the phone at home).
2. Natural - when memory training is combined with in a healthy way life, and the results can be used in any field of human activity.
3. Artificial is the use of mnemonics, the development of which allows you to remember colossal amounts of various information.

It does not matter which method you choose, but if at least one of them is studied, then this will already be a step towards self-improvement and the opportunity to go further. These invaluable skills will undoubtedly come in handy in any area of ​​life, making you successful and happy.

The mystery of human memory is one of the main scientific problems of the 21st century, and it will have to be solved by the joint efforts of chemists, physicists, biologists, physiologists, mathematicians and representatives of other scientific disciplines. And although we are still far from fully understanding what happens to us when we “remember”, “forget” and “remember again”, important discoveries of recent years point the right way.

One of the main problems of neurophysiology is the inability to conduct experiments on humans. However, even in primitive animals, the basic mechanisms of memory are similar to ours.

Pavel Balaban

Today, even the answer to the basic question - what is memory in time and space - can consist mainly of hypotheses and assumptions. If we talk about space, it is still not very clear how memory is organized and where exactly in the brain it is located. These sciences suggest that its elements are present everywhere, in each of the areas of our "gray matter". Moreover, seemingly the same information can be recorded in memory in different places.

For example, it has been established that spatial memory (when we remember a certain environment for the first time - a room, a street, a landscape) is associated with a region of the brain called the hippocampus. When we try to get this situation out of memory, say, ten years later, this memory will already be extracted from a completely different area. Yes, memory can move within the brain, and this thesis is best illustrated by an experiment once conducted with chickens. In the life of newly hatched chicks, imprinting plays a big role - instantaneous learning (and placement in memory is learning). For example, a chicken sees a large moving object and immediately “imprints” in the brain: this is a chicken mother, you need to follow her. But if, after five days, the part of the brain responsible for imprinting is removed from the chicken, it turns out that ... the memorized skill has not gone away. He moved to another area, and this proves that there is one repository for immediate learning outcomes, and another for long-term storage.

We remember with pleasure

But it is even more surprising that there is no such clear sequence of moving memory from operational to permanent, as it happens in a computer, in the brain. Working memory, fixing immediate sensations, simultaneously triggers other memory mechanisms - medium-term and long-term. But the brain is an energy-intensive system and therefore tries to optimize the expenditure of its resources, including memory. Therefore, nature has created a multi-stage system. Working memory is quickly formed and just as quickly destroyed - there is a special mechanism for this. But truly important events are recorded for long-term storage, while their importance is emphasized by emotion, attitude to information. At the level of physiology, emotion is the activation of the most powerful biochemical modulating systems. These systems release hormones-mediators that change the biochemistry of memory in the right direction. Among them, for example, are various hormones of pleasure, the names of which remind not so much of neurophysiology as of the criminal chronicle: these are morphines, opioids, cannabinoids - that is, narcotic substances produced by our body. In particular, endocannabinoids are generated directly at synapses, the junctions of nerve cells. They affect the effectiveness of these contacts and thus "encourage" the recording of this or that information in memory. Other substances from the number of mediator hormones can, on the contrary, suppress the process of moving data from working memory to long-term memory.

The mechanisms of emotional, that is, biochemical reinforcement of memory, are now being actively studied. The only problem is that laboratory research of this kind can only be carried out on animals, but how much can a laboratory rat tell us about its emotions?

If we have stored something in memory, then sometimes the time comes to remember this information, that is, to extract it from memory. But is the word "extract" correct? Apparently, not much. It seems that memory mechanisms do not extract information, but re-generate it. There is no information in these mechanisms, just as there is no voice or music in the hardware of a radio receiver. But everything is clear with the receiver - it processes and converts the electromagnetic signal received by the antenna. What kind of “signal” is processed when the memory is retrieved, where and how this data is stored, is still very difficult to say. However, it is already known that when remembering, the memory is rewritten, modified, or at least this happens with some types of memory.

Not electricity, but chemistry

In search of an answer to the question of how memory can be modified or even erased, important discoveries have been made in recent years, and a number of works devoted to the “memory molecule” have appeared.

In fact, they have been trying to isolate such a molecule, or at least some material carrier of thought and memory, for two hundred years, but without much success. In the end, neurophysiologists came to the conclusion that there is nothing specific to memory in the brain: there are 100 billion neurons, there are 10 quadrillions of connections between them, and somewhere, in this cosmic scale, memory, thoughts, and behavior are uniformly encoded. Attempts were made to block certain chemicals in the brain, and this led to a change in memory, but also to a change in the entire functioning of the body. It was only in 2006 that the first works appeared on the biochemical system, which seems to be very specific to memory. Her blockade did not cause any changes in either behavior or learning ability - only the loss of part of the memory. For example, memory about the situation if the blocker was introduced into the hippocampus. Or about emotional shock if the blocker was injected into the amygdala. The biochemical system discovered is a protein, an enzyme called protein kinase M-zeta, which controls other proteins.

One of the main problems of neurophysiology is the inability to conduct experiments on humans. However, even in primitive animals, the basic mechanisms of memory are similar to ours.

The molecule works at the site of synaptic contact - the contact between brain neurons. Here it is necessary to make one important digression and explain the specifics of these same contacts. The brain is often likened to a computer, and therefore many people think that the connections between neurons, which create everything that we call thinking and memory, are purely electrical in nature. But it's not. The language of synapses is chemistry, here some released molecules, like a key with a lock, interact with other molecules (receptors), and only then do electrical processes begin. How many specific receptors will be delivered through the nerve cell to the place of contact depends on the efficiency, the greater throughput of the synapse.

Protein with special properties

Protein kinase M-zeta just controls the delivery of receptors through the synapse and thus increases its effectiveness. When these molecules are activated simultaneously in tens of thousands of synapses, signals are rerouted, and the general properties of a certain network of neurons change. All this tells us little about how memory changes are encoded in this rerouting, but one thing is known for sure: if the protein kinase M-zeta is blocked, the memory will be erased, because the chemical bonds that provide it will not work. The newly discovered "molecule" of memory has a number of interesting features.

First, it is capable of self-reproduction. If, as a result of learning (that is, receiving new information), a certain amount of protein kinase M-zeta was formed in the synapse, then this amount can remain there for a very long time, despite the fact that this protein molecule decomposes in three to four days. In some way, the molecule mobilizes the resources of the cell and ensures the synthesis and delivery of new molecules to the place of synaptic contact to replace those that have left.

Secondly, to most interesting features protein kinase M-zeta includes its blocking. When the researchers needed to obtain a substance for experiments on blocking the "molecule" of memory, they simply "read" the section of her gene, in which her own peptide blocker is encoded, and synthesized it. However, this blocker is never produced by the cell itself, and for what purpose evolution left its code in the genome is unclear.

The third important feature of the molecule is that both it and its blocker have an almost identical appearance for all living beings with a nervous system. This indicates that, in the form of protein kinase M-zeta, we are dealing with the most ancient adaptive mechanism, on which human memory is also built.

Of course, the protein kinase M-zeta is not a "memory molecule" in the sense in which the scientists of the past hoped to find it. It is not a material carrier of memorized information, but, obviously, it acts as a key regulator of the effectiveness of connections within the brain, it initiates the emergence of new configurations as a result of learning.

Get into contact

Now experiments with the protein kinase blocker M-zeta are, in a sense, "shooting on the squares." The substance is injected into certain areas of the brain of experimental animals with a very thin needle and thus turns off the memory immediately in large functional blocks. The boundaries of penetration of the blocker are not always clear, as well as its concentration in the area of ​​the site chosen as the target. As a result, not all experiments in this area bring unambiguous results.

A true understanding of the processes occurring in memory can be obtained by working at the level of individual synapses, but this requires targeted delivery of the blocker to the contact between neurons. Today it is impossible, but since such a task is facing science, sooner or later the tools to solve it will appear. Special hopes are placed on optogenetics. It has been established that a cell in which the possibility of synthesizing a light-sensitive protein is built in by genetic engineering methods can be controlled using a laser beam. And if such manipulations at the level of living organisms are not yet performed, something similar is already being done on the basis of grown cell cultures, and the results are very impressive.

Neuroscientists from Canada and the United States have found that not all nerve cells that receive the information necessary for this are involved in memorizing simple skills, but only about a quarter of them. Which neurons take part in the formation of long-term memory depends on the concentration of the regulatory protein CREB in the cell nucleus. If you artificially increase the concentration of CREB in some neurons, it is they who will remember. If you block CREB in some neurons, other nerve cells will take over the role of memory cells.

One of the most brilliant achievements of neuroscience in the 20th century was the deciphering of the molecular mechanisms of memory. Nobel laureate Eric Kandel and his colleagues were able to show that for the formation of real memory - both short-term and long-term - just three neurons, connected in a certain way, are enough.

Memory was studied on the example of the formation of a conditioned reflex in a giant mollusk, the sea hare Aplysia. The mollusk was carefully touched by the siphon, and immediately after this, the tail was strongly beaten. After such a procedure, the mollusk reacts for some time to a light touch to the siphon with a violent defensive reaction, but soon forgets everything (short-term memory). If the "training" is repeated several times, a stable conditioned reflex (long-term memory) is formed.

It turned out that the process of learning and memorization has nothing to do with some higher, ideal or spiritual matters, but is completely explained by fairly simple and completely automatic events at the level of individual neurons. The whole process can be fully reproduced on the simplest system of three isolated nerve cells. One neuron (sensory) receives a signal from the siphon (in this case, it feels a light touch). The sensory neuron sends an impulse to the motor neuron, which, in turn, causes the muscles involved in the defense reaction to contract (Aplysia retracts the gill and throws a portion of red ink into the water). Information about the blow to the tail comes from the third neuron, which in this case plays the role of a modulator. A nerve impulse from one neuron to another is transmitted through the release of signal substances (neurotransmitters). The points of interneuronal contacts at which the neurotransmitter is released are called synapses.

Eric Kandel won the Nobel Prize for this picture. This shows how short-term and long-term memory are formed in the simplest system of three neurons.

The figure shows two synapses. The first serves to transmit an impulse from a sensory neuron to a motor one. The second synapse transmits an impulse from the modulating neuron to the end of the sensory one. If at the moment of touching the siphon the modulating neuron is “silent” (the tail is not beaten), little neurotransmitter is released in synapse 1, and the motor neuron is not excited.

However, hitting the tail leads to the release of a neurotransmitter at synapse 2, which causes important changes in the behavior of synapse 1. The signaling substance cAMP (cyclic adenosine monophosphate) is produced at the end of the sensory neuron. This substance activates the regulatory protein - protein kinase A. Protein kinase A, in turn, activates other proteins, which ultimately leads to the fact that synapse 1, when the sensory neuron is excited (that is, in response to touching the siphon), begins to release more neurotransmitter, and the motor neuron fires. That's what it is short term memory: as long as there is a lot of active protein kinase A at the end of the sensory neuron, signal transmission from the siphon to the muscles of the gill and ink sac is more efficient.

If touching the siphon was accompanied by a blow to the tail many times in a row, protein kinase A becomes so abundant that it penetrates the nucleus of the sensory neuron. This leads to the activation of another regulatory protein, the CREB transcription factor. The CREB protein “turns on” a number of genes that ultimately cause synapse 1 to grow (as shown) or cause additional processes to grow at the end of the sensory neuron that form new synaptic contacts with the motor neuron. In both cases, the effect is the same: now even a slight excitation of the sensory neuron is enough to excite the motor neuron. That's what it is long-term memory. It remains to be added that, as further studies have shown, in higher animals and in you and me, memory is based on the same principles as in Aplysia.

After this necessary introduction, you can move on to the story of what Canadian and American neuroscientists actually discovered. They studied the formation of conditioned reflexes associated with fear in laboratory mice. The simplest reflexes of this kind are formed in the lateral amygdala (LA) - a very small part of the brain responsible for the body's reactions to all sorts of frightening stimuli. Mice were taught that after a certain sound is heard, they are shocked. In response to an electric shock, the mouse freezes: this is a standard reaction to fright. Mice are smart animals, they can be taught a lot, and their conditioned reflexes are formed quickly. Trained mice freeze as soon as they hear a sound that portends danger.

Scientists have found that the signal from the neurons that perceive the sound comes to about 70% of neurons in the lateral amygdala. However, changes associated with the formation of long-term memory (growth of new nerve endings, etc.) in trained mice occur only in a quarter of these neurons (approximately 18% of LA neurons).

Scientists suggested that there is a kind of competition between LA neurons, potentially able to take part in the formation of long-term memory, for the right to grow new synapses, and the probability of “success” of one or another neuron depends on the concentration of the CREB protein in its nucleus. To test this assumption, mice were microinjected with artificial viruses that are not capable of reproduction, but capable of producing a complete CREB protein or its non-functional analogue CREB S133A. The genes for both of these proteins, inserted into the genome of the virus, were "sewn" to the gene for the green fluorescent protein of the jellyfish. As a result, the nuclei of those LA neurons that the virus entered began to glow green.

It turned out that as a result of microinjection, the virus penetrates into approximately the same number of LA neurons as is involved in the formation of the conditioned reflex. This coincidence turned out to be quite convenient.

In addition to normal mice, mutant mice were used in the experiments, in which the CREB gene does not work. Such mice are completely devoid of the ability to learn, they cannot remember anything. It turned out that the introduction of a CREB-producing virus into the LA of such mice completely restores the ability to form a conditioned reflex. But perhaps increasing the concentration of CREB in some LA neurons simply enhances the “freeze” response?

To test this, experiments were set up with more complex learning, in which the mouse had to “realize” the connection between the sound and the electric shock not directly, but indirectly, and for this it was necessary to remember the specific context in which the learning took place. For this, the work of the LA alone is not enough, but the participation of the hippocampus is also required. In this situation, the mutant mice could not learn anything, because no viruses were injected into their hippocampus. Therefore, the concentration of CREB affects memory, and not the propensity to freeze.

With the help of a series of additional experiments, it was possible to prove that precisely those LA neurons that were infected with the virus are involved in memorization in mutant mice. The introduction of the virus into the LA of healthy mice did not affect their learning ability. However, as in the case of mutant mice, it was precisely those LA neurons that the virus had entered that participated in memorization.

Another virus that produces CREB S133A deprives infected neurons of the ability to remember, that is, to grow new endings. The scientists suggested that the introduction of this virus into the LA of healthy mice should not, however, reduce their learning ability, since the virus infects only about 20% of LA neurons, and other, uninfected neurons will take on the role of "remembering". And so it turned out. Mice trained normally, but among the neurons that took part in memorization, there were practically no infected (that is, glowing green light).

Scientists conducted a number of more complex experiments, which made it possible to exclude all other explanations, except for one - the one that corresponded to their initial assumption.

Thus, not all neurons that receive the information necessary for this (in this case, “sensory” information about sound and “modulating” information about electric shock) participate in memorization. Only a certain part of these neurons, namely those with more CREB protein in their nuclei, take on the honorable role of memory ones. This, in general, is logical, since the high concentration of CREB in the nucleus just makes such neurons the most “predisposed” to the rapid growth of new endings.

What remains unclear is the mechanism by which other neurons know that the job has already been done, the winners have been named, and they themselves no longer need to grow anything for themselves.

This mechanism can be quite simple. A completely similar regulatory system is known in filamentous cyanobacteria, the filaments of which consist of two types of cells: ordinary, involved in photosynthesis, and specialized "heterocysts", engaged in atmospheric nitrogen fixation. The system works very simply: when the community lacks nitrogen, photosynthetic cells begin to turn into heterocysts. The process is reversible up to a certain point. Cells that have gone far enough along this path begin to secrete a signaling substance that prevents neighboring cells from turning into heterocysts. The result is a thread with a certain well-defined ratio of ordinary cells and heterocysts (for example, 1:20), and the heterocysts are located approximately at an equal distance from each other.

In my opinion, to call such regulatory mechanisms "competition", as the authors of the article do, is not entirely correct, the emphasis here should be different. The neuron does not receive any personal benefit from the fact that it is he who will take part in memorization. In my opinion, it is more appropriate to talk here not about competition, but about real cooperation itself.

According to materials: Jin-Hee Han, Steven A. Kushner, Adelaide P. Yiu, Christy J. Cole, Anna Matynia, Robert A. Brown, Rachael L. Neve, John F. Guzowski, Alcino J. Silva, Sheena A. Josselyn. Neuronal Competition and Selection During Memory Formation 2007. V. 316. P. 457–460.