On the model, you see two selected areas, they are isolated, that is, the neurons belonging to these regions do not act on each other, unless of course connected by synapses directly. I conditionally designated these two areas as “hippocampus” (the area below) and “cortex” (the area on top). There is also a reflex with the heading “R” leading to a reflex response “1”. This reflex has two representations in the hippocampus and cortex, these are two groups of white neurons. And also there are two receptor neurons associated with the “E” receptor in each region, these neurons are indifferent, and activation of them will not lead to any answer, but will create little activity. The main thing is that the neuroplasticity for these two area is different, in the area designated as the hippocampus the plasticity is higher than in the area of ​​the cortex.

If we activate the reflex with the heading “R” and the unconditioned stimulus “E”, approximately in one time interval, then a new reflex arc will occur, but most likely this will occur in the region with high neuroplasticity.

The reflex formed only in the region with high neuroplasticity will be fully functional, but can be lost because under the influence of other stimuli neurons can retrain. The hippocampus is considerably smaller than the cortex, but it contains practically all the representations that are present in the cortex. The need for the formation of new connections all the time makes use of cells that have already participated in the formation of reflexes.

Loss of reflex in the area of high neuroplasticity

If we continue training by combining the stimuli “E” and “R”, then after a certain number of repetitions a reflex arc will form in the region with a low neuroplasticity.

Now the reflex is more securely protected, even if it disappears from an area with high neuroplasticity, it will still be performed.

Of course, retraining of neurons in an area with low neuroplasticity is possible, but this will take more time and effort.

Thus, there are two stages of memorization: before the formation of the reflex in the cortex and after. Preservation of a copy of a reflex not only in the hippocampus but also in the cerebral cortex is a hierarchical consolidation of memory.

But how is it with information that is remembered immediately and for a long time, usually such information is accompanied by some emotional experiences.

Our pain receptors are associated with the brain department, called the amygdala. The amygdala controls the area of the nervous system the locus coeruleus, which consists of norepinephrine neurons. The axons of these neurons have endings in all areas of the brain, their task is to deliver norepinephrine as needed to as many cells as possible.

Norepinephrine in our case is a signal to increase neuroplasticity. This is a kind of “now print” team and under the influence of norepinephrine nerve cells try to make changes as soon as possible. And accordingly, when the actions of norepinephrine cease cells return to their working state, retaining all the changes that have occurred to them.

So, let’s look at this in the model.

The areas in the program not only logically separate and isolate the neurons, but it is also possible to configure some interaction scripts for these areas.

Objects of a network of a higher level are different areas of the brain. The nature of their interaction in the system is special, the activity of one region can lead to the inhibition of all neurons, or to have a modulating character, or to influence neuroplasticity in another area. Feeling of fear (tonsil activity) leads to an increase in the sensitivity of neurons in the motor cortex, modulation takes place to reduce the activation threshold of neurons. Therefore, when fear embraces us, we can run away from danger faster, our muscles do not become stronger, we just need less inner motivation for action.

In this case, there is a scenario whereby when an activity occurs in the area called “amygdala” in the “cortex” area, the neuroplasticity increases for two seconds.

Without the activation of the amygdala:

With the activation of the amygdala:

Thus, it turns out that in a state of stress, learning occurs in the cortex as quickly as in regions with high plasticity. For example, it can also be verified by studying experimental work on mice.

P — neuroplasticity (0 ≥ P ≥ 1)

The hierarchical memory system can be represented as follows. There are several isolated areas, in each subsequent neuroplasticity will be smaller, and therefore, each next area will be less affected by changes. In each such area there will be a representation of the stimulus. And it will also be possible to control the memory speed by means of signals that lead to a short-term change in neuroplasticity.

On the one hand, we have a certain information filter that allows you to save information that is more often repeated, on the other hand, the ability to instantly remember important information for the organism.

Images

To study human memory only on the basis of the simplest conditioned reflexes is incorrect, for many it may seem very primitive with respect to the information that a person can operate on. And so we’ll talk about such a concept as an image, and how images are formed on the level of nerve cells.

The system of formation of images in the brain is associated with the phenomenon of neuronal specialization observed in biology. When studying the brain it was found that some neurons selectively react to a certain type of stimulus, that is, a certain group of neurons in your brain will be activated when you see or think about an animal, there are also groups that will react only, for example, on the face of your grandmother. There is even a name for this phenomenon of neuron specialization “grandmother cell”.

Let’s consider the mechanism of obtaining specialization by neurons on the model.

We have a receptor field of 12 receptors (Q, W, E, R … V), all receptors are the same, are in equal conditions. And each receptor has a representation (a receptor neuron) in a group of interconnected cells located in a plane, similar to how it is organized in a fragment of the cortex that processes signals from the senses. This will be the area of primary processing and therefore the neurons in this area have very high neuroplasticity (P = 1).

If, for example, three receptors (Z, X, R) are activated from the receptor field, then the same principles of attraction of excitation that underlie the formation of conditioned reflexes lead to the fact that the excitation will converge in one place. Moreover, the level of the activating effect on the neuron at this site will be higher because the activating signals come from different sides almost simultaneously. Thus, the specialization of neurons is automatically formed, in this case neurons that react to the complex stimulus “Z + X + R” are determined.

And of course you can see that this system for forming image regions is very inaccurate. The regions of the images may intersect, and it is also possible that quite different groups of stimuli can be attached to the same region. And such an inaccuracy in the work of the brain can have a rather positive character. After all, in the recognition of images, accuracy can only interfere, and it also reveals the potential for creativity because combining previously incompatible or seeing something different in the image is possible only because these images are not so unambiguous and do not have clear boundaries. This also explains why human perception can be deceptive.

But in order to identify these areas of an increased level of activating action, it is necessary to add one more group of neurons that will be activated only in the case of obtaining such an increased effect. About the structure of the cortex and the organization of the cortex, we will talk in more detail in future articles, as well as on how to improve the image formation mechanism qualitatively.

Now let’s connect the hierarchical system of memory and the system of formation of mental images.

Excitation from one stimulus can go in different ways before reaching the next level of processing. So the path that chooses nervous excitement is determined by the influence of other stimuli. This path determines which representation of a higher level will be excited and so higher in the hierarchy. Given the difference in plasticity at the levels, the images at higher levels will be more stable, namely, if the complex stimulus is not fully or noisily activated, then the area that will be more typical for the given complex stimulus will still come to activity.

Such a memory structure is similar to a tree, for example, at the first levels we can isolate neurons that will react to all faces of people, higher in hierarchy we find neurons reacting to faces of familiar people or those individuals that we have seen repeatedly and the last levels will reveal the faces of relatives , whose faces are very familiar to us. The face of our grandmother, which we can identify even in a very distorted, incomplete or noisy form, because at high levels the neuroplasticity is very low and the fuzzy selection of the “branch” will still lead to its full activation.

This memory structure explains the reason for the high speed of information extraction, the excitation from the receptors simply passes through all layers of processing, influencing each other, these signals determine the path through which excitations come to the right groups of neurons. Here there is no search of information and there are no comparison operations, with any reference information, etc. Evolution was along the path of speed, not accuracy, although the accuracy of perception was achieved by increasing the receptor fields and special ways of organizing the brain.

LTP

Discourse on memory would not be complete unless we touch upon the topic of long-term potency. This effect is due to the fact that when the nerve cell is exposed to a strong activating action, its sensitivity is increased for some time, and the time of this change in the cell can last from several minutes to several weeks. Advantageously, this effect is manifested in large pyramidal cells of the hippocampus, although it may be observed in other areas but in a lower concentration.

Under the influence of increased impact in the cell, a specific cascade of chemical reactions is triggered, which leads to the formation of a postsynaptic membrane of additional receptors, which increases the sensitivity of the cell. Let’s imagine how this will be implemented in the model.

Consider the summation scheme in neurons that represents a vessel filled with a mediator, from which a continuous waste of this mediator occurs. If the level of the mediator in the vessel reaches the value “A”, then the activation of the neuron takes place. If the level of the activating effect reaches the “B” value, not only activation of the neuron will occur, but in addition, the main activation threshold “A” will decrease to the level “C”, these changes will be temporary.

This feature in the work of some cells of the hippocampus goes against the principles of habituation in the nervous system. Thanks to her, the organism can remember what happened to him a few minutes ago. If you close your eyes and for a while will be in silence, you do not even need to open your eyes to recall information about where you are and what events happened earlier. The surprising thing here is that there are no stimuli that will activate the reflex arcs leading to the neurons that are responsible for this information.

In the process of activity in the hippocampus, marking of regions and neurons by means of long-term potentiation occurs, those areas that are responsible for active images are labeled. This makes it easy to return to images that have recently been activated, even through a weaker impact.

Imagine that there are groups of neurons responsible for the images of places, for example, images: “job”, “house”, “street”, etc. Then, being in the workplace, we can receive a lot of visual, auditory, tactile images and signs indicating where we are. This leads to the fact that the neurons associated with the image of the place will be marked by long-term potentiation. Now, at a certain time interval, while long-term potentiation is in effect, a small stimulus from the root image of the place is enough to make the neurons of the corresponding image activated.

The received theory of memory, in my opinion, is very simple and laconic, and it follows from the foundations laid down in the work of neurons.

In the next article, we’ll talk about emotions, and I hope to convince you that the most complex emotions in a person’s understanding will be available for electronic brains.

A link to the simulator of nervous systems can be found in the first article.