Structure and homepage settings of the brain

Knowledge of how the neuron is insufficient for understanding what is reasonable and intelligent behavior. Evolution has done amazing skill by creating a system of relatively simple elements, capable of hitting incredible success in interaction with the environment.

It is not enough to take a mass of connected neurons (even adding layers) to connect the sensors and conclusions and to at least some semblance of a brain. Main field of work of evolution over millions of years is not a neuron, and the structure and organization of nerve cells in the nervous system.

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Let us look at the way the cerebral cortex, the structure through which Man has become the most successful species on Earth.

It is known that the bark of the big hemispheres of the human brain consists of six conventional layers, but in this form it came in many stages of evolution. So to start we will consider the simplified variant with 2 – 3 layers, because such an option in nature. Any biological structure is more profitable to examine from the perspective of its evolutionary development. Evolution was two ways of development of the cortex: the increase in the number of layers and the increase in the total area of the cortex.

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The second feature of the cortex is the presence of the so-called cortical columns. We can say that the cortical column is a logical unit of the structure of the crust. The growth of the cortex during embryonic development is carried out by division, self-replication of entire columns. This is logical, if we want to keep some structure during the growth.

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The basis of cortical columns are pyramidal neurons. Pyramidal neurons are among the largest neurons in the nervous system, and therefore the most studied, since their dimensions allow to influence them with the help of special electrodes without destroying the cells.

These neurons have a well-developed system of dendrites that extends throughout the column and the axon which in some cases is the source of an incoming or outgoing signal. Despite the fact that such neurons in the first layers of cortical columns may be a few, they all work as one nanoelement. The activity of one pyramidal cell often means the activity of the whole group of cells.

The evolutionary development of the nervous system was focused primarily on reliability and the duplication or distribution of the same functional on the group of cells is a General phenomenon. It is impossible to imagine a scheme created by the nature in which the death of only a single cell would result in disruption of a functional unit. We can say that the activity of groups of pyramidal cells in the column indicates the activity of the speaker.

Speakers can be divided into two types: formative signal and the receiving signal. The type of the column depends on what are the axons from pyramidal neurons: afferent or efferent. If there is an afferent axons, that is, generating a signal, the column will be activated upon receipt of a signal may relay the signal, if you will, and the efferent axon. In the presence of efferent axons of the result of the activity of the column is a formation of the outgoing signal.

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The dendrites of pyramidal neurons reaching the upper layers of the cortex, where outside its cortical column, thus there is a local interaction between neighbouring columns. One of the forms of local interaction is the lateral (side) braking.

Inhibition of neighbouring columns is carried out by special inhibitory neurons, which are part of the cortical columns. Mainly inhibitory neurons exert their effects on pyramidal neurons, preventing their activation.

Lateral inhibition is on the nearby surrounding of the column. It allows you to make border areas of active speakers clearer and the field of activity more localized. Due to lateral inhibition there is an obstacle to a strong spread of excitation.

In addition to the lateral inhibition is present and the lateral impression. Adjusting the balance between these two factors there is the possibility of very finely adjust the level of General activity in the brain. For example, sleep need to reduce the level of activity it is necessary to strengthen the lateral inhibition and weaken the urge. This is done by special chemical signals and mediators.

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Not always the effect on the adjacent column has the shape of a concentric uniform distribution entorhinal cortex peculiar distribution, which allows the excitation is easier to spread in a triangular mesh. This so-called grid cell, which helps animals to navigate in space, by an additional modification of the image of the place of stay.

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The next element of the cortical column is the layer of the plurality of relatively small stellate neurons. Such a layer generally called a granular. The neurons in this layer because of its dimensions is less explored than pyramidal neurons.

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It is the neurons in this layer you can assign the main role in the computational processes of the brain, because of their work and the formation of associative ties and the formation of images. "Calculation" occur by vzaimovliyaniya excitation. The neurons of the granular layer is the associative neuroelement.

And pyramidal cells play the role of a simple adder, as these elements would be separated, isolated images. Pyramidal neurons will be activated upon excitation a significant part of the neurons of the granular layer of the column.

The connection between the stellate neurons are free to go beyond the boundaries of their cortical columns, we can say that a granular layer is almost solid.

Memory, memory consolidation and grandma's neurons

This option cortical columns and structure of the crust is very simple and may even seem primitive, but when used on a large scale when properly configured, it is possible to obtain a structure with high computational performance. Nature always chose the most simple, reliable and effective solutions and our nervous system is no exception to this rule.

Often faced with the opinion that the neuron is similar to some superficiality or quantum computer, which makes complex calculations using some oscillations of ions on the membrane or quantum mechanisms. Even the algorithm of summation in neurons of the usual perceptron is more complex than in the biological analog, the perceptron has a value from any of the synapses receives signals and biological important only the total amount of exposure. Stereotypical thinking about the unattainable complexity of the brain may interfere with the understanding of the nature of the biological system.

Surprisingly, the structure is versatile to different types of regions of the cortex: sensory, motor and associative. Possible variations of the relative thickness of the various layers depending on the function of the cortical area. For example, the motor cortex enhanced layer pyramidal neurons in relation to the granular layer, because the signals of the motor cortex needs to be clear and strong. And associative areas of increased inherent layer of stellate neurons to provide the greatest flexibility in the formation of associative reflex arcs.

Cortical area bound by many ties, it is thanks to AXOS, the long processes of neurons. Bundles of axons form a nerve, which is the so-called white matter. These nerves can associate as a neighboring region and in the region of the opposite half of the brain. Moreover, the architecture of these connections due to the evolutionary development of the brain and partly learned experience and instigation, but for different people the picture of these relations will be similar. There are several research projects related to the mapping of these relations, for example, Human Connectom Project.

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Let's look at how organized the data connection.

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The scheme is only an example for understanding the principles of the organization. Real circuit in the biological nervous system much more difficult.

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Imagine a receptive field with a number of similar receptors, allowing to obtain about the environment some information. Certain receptive fields form a combined signal, for example, the retina of the eye. Such signals require specific analysis capabilities.

The representatives of the speakers of these receptors are distributed across sensory cortex with a certain density, preserving the topology of an arrangement of receptors in the receptive field (A). The principles of the mutual attraction of excitation on the cortex will be formed in certain areas of excitation, which will be the image of the received combined signal.

The primary sensory cortex typically has the highest neuroplasticity, i.e., any combination of the excited columns will be processed without taking into account previously obtained information. The resulting image will be readable by other speakers, also with a certain density are distributed in the sensory cortex. These speakers will transmit the information for further processing the following regions of the cortex.

The nature and density "reading" columns give the defined filter to the received images. It is not difficult to understand that this way of processing leads to considerable loss of information received from receptors, the resulting images do not give a clear information what kind of receptors was activated. Evolution selected two ways to resolve this issue.

First, it is the excess number of receptors that compensate for the decline in the information content after treatment. Secondly, if you duplicate the information from the receptors in a different area, but with the violation of the topology of an arrangement of speakers-representatives in relation to the location of receptors in the receptive field (B), i.e. they get confused.

While many different combinations of activity of the receptor in two areas will form different combinations of images, which gives you more informative and more signs that we can identify. Of course it should be understood that the "tangling" of the signals takes place in a specific way, for example, if "confused" in the retina of the eye no good it will not.

Tangling occurs in small fragments of the receptor fields. And of course we can, if necessary, to duplicate and confuse the signals more than once. In the nervous system as an example of this separation is called the dorsal and ventral path processing of visual signals.

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The General principle of information processing by the cerebral cortex is a serial transfer of information from region to region with lower density of ties. And with each subsequent level the neuroplasticity areas is reduced, which adds to the computation, memory and experience in processing previous information.

The processed information may be released some key characteristics that are associated with specific nerve cells. Simply put, areas of the cortex higher level processing will be formed is the shape of the distribution of excitation, which corresponds to the most frequent form of the processed signal.

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Generated image of "abc" combination of columns a, b and c frequent repetition, emotional reinforcement, will occur in the future, even if incomplete and noise-activated combination.

At each level of information processing takes time, you need to analyze the dynamics of changes of information in time, it is possible to produblirovat pieces of information from each level into one area.

The analogue in biology is the area of processing of visual information MT (V5) middle temporal cortex in which information is collected from areas V1, V2, V3..., this area is responsible for perception of motion. When damage to this area occurs akinetopsia – inability to perceive movement.

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The associative region is arranged relatively simple, there are the representations of different sensory and motor areas. And for motor representations important for bilateral relations, or it is the axons which can work in both directions, or it is adjacent and co-working speakers on both ends, or two axon of one column working in a variety of ways.

Such areas should be a lot of different location representations, to possibility of the formation of reflex arcs for the different combinations was equally likely. Such areas are formed conditional reflexes, and therefore these areas should have a low plasticity.

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All connections in the engine and primernih areas should be bilateral in nature, it is necessary for the formation of associative connections. Essentially promotora region should form a reflex arc sequence from one point of excitation to another. That would be more variability you need representation, leading to action repeatedly stir, it was like touch processing only in reverse order. All motor actions interact with a specially arranged area coordinating action in time – cerebellum.

The schemes are a simplification of how it tripled in the brain, and to create logical structures similar to the human nervous system is impossible without participation of specialists in the field of neuroscience and scientists studying the connectome.

But what about other layers?! – Indeed, the only one I told about the three layers of the cortex, but in human brain there are six layers in the cerebral cortex. The cortex was a quite successful product of evolution even in the presence of a small number of layers. The principle of evolution: what works – do not touch.

Therefore, all new layer in the cortex is an add-on to the existing layers. If you understand the layers of the human brain, we can see that we have six visible layers, and two logical layers, the structure of which is similar and repeated. Evolution just repeat the already existing structure to increase productivity.

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Pyramidal cells of the outer layer smaller than pyramidal cells in the first layer, and hence generally have a higher threshold of sensitivity to the activating factors. The granular layer will work in similar conditions, but presumably stellate neurons in the outer layer have lower plasticity, so that under certain conditions the pattern of activity in the granular layer may vary, despite the fact that the incoming signals will be the same.

Due to these two logical layers there are two modes of activity of a cortical column. The first mode is full of activity, code pyramidal cells of both layers are activated, activates the full column in its entirety. Second: partial activity when activated only the upper additional layer. These two modes of operation of the column can be compared with a person's ability to speak in full voice and whisper, the whisper is a partial activity, full voice is full of activity.

What gives? For the sensory cortex is an additional level of information processing, as well as the ability to work with images of these regions without activation via receptors. In other words, it gives the opportunity to work with imagination. For associative areas is an additional level of abstraction, the formation of associations between the images having less common characteristics, as the sensitivity threshold of the pyramidal cells of the additional layer is higher.

For engine and premotornoj crust is an opportunity to work through some movements without of executing it. Only with the full activation of a column the actions take place, actions in case of partial activation remain in our imagination.

Of course, there are areas in the brain that control play modes of the columns, as we can very easily change the nature of our speaking with a whisper at full power. If you increase the level of inhibition in the column, it is possible that it will be activated only partially, if on the contrary disinhibited column, some ideas can immediately be translated into action.

Imagination and a high level of abstract thinking made man the most successful species on Earth.

Even if we properly set region and the relationship between them does not suffice to obtain the current model. Necessary unconditioned reflexes. Man is born with a rich set of reflex mechanisms carefully selected by evolution.

Tuning reflexes for the model is important, considering the fact that learning new reflexes occurs always on the basis of existing reflexes. If any action is not involved in any unconditioned reflex, you will be taught to control that action will be impossible.

In biological systems initially did not put "clear" reflexes. After the birth we can't control our limbs, or, for example, to walk. This is due to the fact that it is impossible to determine in advance some of the parameters of the body, the size of the limbs, their weight, the force generated by muscles, etc. and these parameters and even change dynamically during growth of the organism.

So many unconditioned reflexes are in response to a field of action, and in the header field, activates its receptors. Also lays an emotional mechanism that is associated with the unconditioned reflexes, which will trigger the reflexes to adjust to a certain point of development.

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Consider the adjustment mechanism of the reflexes on the example of baby talk. In accordance with a certain stage of development starts the mechanism of babbling, i.e. there is almost a spontaneous launch of "fuzzy" reflexes. When launched, the child begins to pronounce the various sounds, sometimes these reflexes are triggered and heard a sound from outside.

The spoken sounds often do not match the expected, i.e. do not correspond to sounds reflex triggering, or triggering a hypothetical. The child hears produced his own sounds, getting feedback between the team and the resulting action. Further, by entering the emotional mechanism of novelty, which connects the center needs novelty with speech act which gives a new Association between the audible sound and the inner motive that prompted to action.

That leads to a multiple repetition of the steps leading to the saturation of the feelings of novelty. It is alleged that the child in the period of babbling pronounces all the sounds of all languages on Earth. The repetition of sounds leads to the formation of clear images of action in accordance with the desired result.

Similarly, the mastery of the motor system. Initially, the movement of babies almost chaotic, there is only an increase in motor activity as a response to emotional stimulus. But over time, maps of movements and visual perception, tactile perception and body position.

Some unconditional reflexes are not as primitive in certain cases, the nervous system laid the template images, and to transfer such patterns from biological systems to computer model virtually impossible. Man has the innate ability to recognize the emotions and movements of individuals of the species. Therefore, in respect of some aspects of training will be necessary to apply some workarounds.

That would bypass the lengthy process of learning a motor system through numerous attempts at crawling, standing, walking and series of downs for robots. it is possible to apply the method of control.

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People can pass on their experience to control the robot body by means of special devices and technology of motion capture. In the model of the nervous system of the robot with the intercepted control when motor actions are to be activated representations, as if these movements were performed the robot.

Thanks to what would form the necessary images and associative relations. For example, while training with the team: "Raise your hands" — a training mode of the motion capture itself raises their hands, it would lead to the formation of a conditioned reflex between the team and the action, and would form an associative link between the team and the image formed by the processing of the position sensors of the body.

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In the process of learning electronic model of the brain is always possible to control the plasticity desired fields and have the ability to look "inside" of the learning process, and to allocate, to identify and strengthen the images. That should significantly speed up the learning process of artificial neural systems in relation to the training person. As has become clear, the model built on the above principles, will be trained for the most part like a man, without separation of training and interaction with the environment.published  

 



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Source: geektimes.ru/post/280604/