I still remember the action movie "Johnny the Mnemonic". There K. Reeves implanted a flash drive into the brain and uploaded unmeasured amounts of information there. How cool it is to remember everything! But Sherlock Holmes called memory - the attic. If you throw everything there and store it for many years, then it will be impossible to find it there quickly, and maybe it will not work at all. Therefore, he remembered only what he needed in his work.
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, then it is still not very clear how memory is organized and where exactly it is located in the brain. Science data suggest that its elements are present everywhere, in each of the areas of our "gray matter".
Moreover, one and the same, seemingly, information can be written into 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 an area of the brain called the hippocampus. When we try to get this situation out of our memory, say, ten years later, then 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 carried out with chickens. Imprinting plays an important role in the life of newly hatched chickens - instant learning (and memory placement is learning). For example, a chicken sees a large moving object and immediately "imprints" in the brain: this is a mother chicken, 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 anywhere. It has 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 the brain does not have such a clear sequence of movement of memory from operational to permanent, as it happens in a computer. Working memory, which records 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 use of its resources, including memory. Therefore, nature has created a multistage system. Working memory is quickly formed and just as quickly destroyed - there is a special mechanism for this. But really important events are recorded for long-term storage, while their importance is emphasized by emotion, attitude to information.
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At the physiological level, 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, but of criminal chronicle: these are morphines, opioids, cannabinoids - that is, drugs produced by our body. In particular, endocannabinoids are generated directly at synapses - the contacts of nerve cells. They influence the effectiveness of these contacts and, thus, "encourage" the recording of this or that information in memory. Other substances from the number of hormone-mediators can, on the contrary, suppress the process of transferring data from working memory to long-term memory.
The mechanisms of emotional, that is, biochemical memory reinforcement 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 our memory, then sometimes it comes time to remember this information, that is, to extract it from memory. But is the word "extract" correct? Apparently, not very much. It seems that memory mechanisms do not retrieve information, but regenerate 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 to the antenna. What kind of "signal" is processed when retrieving memory, where and how this data is stored, is still very difficult to say. However, it is already known that during recollection, 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 you can modify or even erase memory, important discoveries have been made in recent years, and a number of works have appeared on the "memory molecule".
In fact, they have tried 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 quadrillion connections between them, and somewhere out there, in this cosmic-scale network, memory, thoughts, and behavior are uniformly encoded. Attempts have been made to block certain chemicals in the brain, and this has 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 on the biochemical system appeared, which seems to be very specific for memory. Her blockage did not cause any change in behavior or learning ability - only the loss of some of her memory. For example, the memory of the situation,if the blocker has been injected into the hippocampus. Or emotional shock if a blocker was injected into the amygdala. The biochemical system found is a protein, an enzyme called protein kinase M-zeta, which controls other proteins.
One of the main problems of neurophysiology - the inability to conduct experiments on humans. However, even in primitive animals, basic memory mechanisms are similar to ours.
The molecule works at the site of synaptic contact - contact between neurons in the brain. Here we must make one important digression and clarify the specifics of these very 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 this is not the case. The language of synapses is chemistry, here some secreted molecules, like a key with a lock, interact with other molecules (receptors), and only then do electrical processes begin. The efficiency and high throughput of the synapse depend on how many specific receptors will be delivered through the nerve cell to the site of contact.
Protein with special propertiesProtein kinase M-zeta just controls the delivery of receptors to the synapse and thus increases its efficiency. When these molecules are turned on at the same time in tens of thousands of synapses, signal rerouting occurs, and the general properties of a certain network of neurons change. All this tells us little about how changes in memory are encoded in this rerouting, but one thing is for certain: 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 additive in the form of a certain amount of protein kinase M-zeta is 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. Somehow, 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 the ones that have left.
Secondly, one of the most interesting features of the M-zeta protein kinase is its blocking. When the researchers needed to obtain a substance for experiments on blocking the memory "molecule", they simply "read" the section of her gene, which encodes her own peptide blocker, 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 things with a nervous system. This indicates that in the person of protein kinase M-zeta we are dealing with the most ancient adaptive mechanism on which human memory is also built.
Of course, protein kinase M-zeta is not a "memory molecule" in the sense in which scientists of the past hoped to find it. It is not a material carrier of memorized information, but, obviously, acts as a key regulator of the effectiveness of connections within the brain, initiates the emergence of new configurations as a result of learning.
Make contact
Now experiments with the blocker of protein kinase M-zeta have in some sense the character of "shooting across the area." The substance is injected into certain parts of the brain of experimental animals with the help of a very thin needle and, thus, turns off memory immediately in large functional blocks. The boundaries of the blocker's penetration 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 provided by work at the level of individual synapses, but this requires targeted delivery of a blocker into contact between neurons. Today it is impossible, but since such a task is facing science, sooner or later the tools for its solution will appear. Special hopes are pinned on optogenetics. It has been established that a cell in which the ability to synthesize 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 have not yet been performed, something similar is already being done on the basis of grown cell cultures, and the results are very impressive.
Author - Doctor of Biological Sciences, Corresponding Member of the Russian Academy of Sciences, Professor, Director of the IVNDiNF RAS