From the retina, signals are sent to the central part of the analyzer along the optic nerve, which consists of almost a million nerve fibers. At the level of the optic chiasm, about half of the fibers pass into the opposite hemisphere of the brain, the remaining half enters the same (ipsilateral) hemisphere. The first switching of optic nerve fibers occurs in the lateral geniculate bodies of the thalamus. From here, new fibers are sent through the brain to the cerebral visual cortex (Fig. 5.17).
In comparison with the retina, the geniculate body is a relatively simple formation. There is only one synapse here, since the incoming fibers of the optic nerve end on cells that send their impulses to the cortex. The geniculate body contains six layers of cells, each of which receives input from only one eye. The upper four are small-celled, the lower two are large-celled, so the upper layers are called parvocellular(parvo - small, cellula - cell, lat.) and the lower ones - magnocellular(magnus - large, lat.)(fig.5.18).
These two types of layers receive information from different ganglion cells associated with different types of bipolar cells and receptors. Each cell of the geniculate body is activated from the receptive field of the retina and has “on” or “ofrV-centers and the periphery of the opposite sign. However, between the cells of the geniculate body and the ganglion cells of the retina, there is
Rice. 5 17 Transmission of visual information to the brain. 1- eye; 2 - retina; 3 - optic nerve; 4 - visual crossover; 5 - external geniculate body, 6 - visual radiation; 7 - visual cortex; 8 - occipital lobes (Lindsney, Norman, 1974)
the brain is the physical basis of vision. Most of the pathways leading from the retina to the visual cortex at the back of the hemispheres pass through the lateral geniculate body. On the cross section of this subcortical structure, six cell layers are visible, two of which correspond to magnocellular bonds (M), and four correspond to parvocellular (P) (Zeki, 1992).
There are differences, of which the most significant is the significantly more pronounced ability of the periphery of the receptive field of the geniculate body cells to suppress the center effect, i.e., they are more specialized (Huebel, 1974).
The neurons of the lateral geniculate bodies send their axons to the primary visual cortex, also called zoneVI (visual - visual, English). Primary visual (striatal) the cortex consists of two parallel and largely independent systems - magnocellular and parvocellular, named according to the layers of the thalamic geniculate bodies (Zeki and Shopp, 1988). The magnocellular system is found in all mammals and therefore has an earlier origin. The parvocellular system is present only in primates, which indicates its later evolutionary origin (Carlson, 1992). The magnocellular system is included in the analysis of the shape, movement and depth of the visual space. The parvocellular system is involved in visual functions developed in primates such as color perception and fine detail (Merigan, 1989).
The connection between the geniculate bodies and the striatal cortex is carried out with high topographic accuracy: zone VI actually contains a “map” of the entire surface of the retina. Damage to any part of the nerve pathway connecting the retina with zone VI leads to the appearance fields of absolute blindness, the dimensions and position of which exactly correspond to the length and lo-
damage in zone VI. S. Henschen named this zone cortical retina (Zeki, 1992).
Fibers coming from the lateral geniculate bodies are in contact with the cells of the fourth layer of the cortex. From here, information ultimately spreads to all layers. Cells in the third and fifth layers of the cortex send their axons to deeper structures in the brain. Most of the connections between the cells of the striatal cortex are perpendicular to the surface, the lateral connections are predominantly short. This allows us to assume the presence of locality in the processing of information in this area.
The area of the retina, which acts on a simple cell of the cortex (the receptive field of the cell), like the fields of the neurons of the retina and geniculate bodies, is divided into “on” and “offr-regions. However, these fields are far from the correct circle. In a typical case, the receptive field consists of a very long and narrow “op” -area, which is adjoined on both sides by wider “og” -sections (Huebel, 1974).
At the same time, despite a split second delay, the brain-computer-Internet-computer-brain interface implemented by scientists allowed one person to control the movements of another person. Due to the fact that this work is being carried out under the auspices of the US Army Research Office, it is not surprising that the last demonstration used a shooting game and simulated actions with explosive devices. The US military sees this technology as an opportunity, through direct communication, to circumvent the language barrier and differences in experience between two people who need to work together to do some possibly dangerous work.
The first demonstration of the functionality of this system was carried out last year. And the current demonstration not only confirmed the efficiency of the idea itself, but also showed some of its expanded capabilities. As before, one of the participants, the one who remotely controls the actions of another person, puts on EEG sensors, with the help of which the computer reads pictures of the brain activity of certain parts of the brain. This data is digitized and transmitted via the Internet to another computer, which performs the entire sequence in reverse order. The second person, the performer, is under the influence of a magnetic field induced by a coil aimed at the area of the brain that controls hand movements. A human operator can send a command to another person and for this he does not even need to move, he just needs to imagine that he is moving his hand. The performer receives commands from the outside using the technology of transcranial magnetic excitation and his hands move independently of his consciousness.
In their experiments, the researchers tested the system's performance on three pairs of participants. The operator and the contractor were always in two buildings, the distance between which was 1.5 kilometers and between which only one digital communication line was laid. “The first operator was involved in computer game, in which he had to defend the city from attack, using weapons of various types and shooting down missiles launched by the enemy. At the same time, he was completely deprived of the possibility of physical impact on game process... The only way the operator could play the game was by mentally controlling the movements of their hands and fingers, the researchers from Washington write. - The accuracy of the game varied greatly from pair to pair and ranged from 25 to 83 percent. And the biggest error rate fell on the error of executing the “fire” command ”.
Researchers have now received a $ 1 million grant from the W. M. Keck Foundation to help them continue and expand their field of research. As part of the new stage, the researchers are going to learn how to decode and transmit more complex brain processes, expand the number of types of transmitted information, which will make it possible to implement the transmission of concepts, thoughts and rules. Thanks to this, at least scientists are counting on this, it will be possible to implement such fantastic technologies in the near future, with the help of which, for example, brilliant scientists will be able to transfer their knowledge to their students directly, or virtuoso musicians or surgeons will be able to remotely perform operations by acting by the hands of others. of people.
The composition of the human brain includes structural and functionally interconnected neurons. This mammalian organ contains between 100 million and 100 billion neurons, depending on the species.
Each mammalian neuron consists of a cell - an elementary structural unit, dendrites (short process) and an axon (long process). The body of an elementary structural unit contains a nucleus and cytoplasm.
Axon leaves the cell body and often spawns many small branches before reaching the nerve endings.
Dendrites extend from the body of the nerve cell and receive messages from other units of the nervous system.
Synapses- these are the contacts where one neuron connects to another. Dendrites are covered with synapses that are formed by the ends of axons from other structural and functional units of the system.
The composition of the human brain is 86 billion neurons consisting of 80% water and consuming about 20% of the oxygen intended for the whole organism, although its mass is only 2% of the body weight.
How signals are transmitted in the brain
When units of a functional system, neurons receive and send messages, they transmit electrical impulses along their axons, which can vary in length from a centimeter to one meter or more. it is clear that it is very difficult.
Many axons are covered with a multi-layered myelin sheath, which speeds up the transmission of electrical signals along the axon. This shell is formed using specialized structural units of the glia. In the organ of the central system, glia is called oligodendrocytes, and in the peripheral nervous system, it is called Schwann cells. The brain center contains at least ten times more glia than the units of the nervous system. Glia has many functions. The importance of glia in the transport of nutrients to neurons, purification, processing of a part of dead neurons.
To transmit signals, the functional units of the body system of any mammal do not work alone. In a neural circuit, the activity of one structural unit directly affects many others. To understand how these interactions govern brain function, neuroscientists study the connections between nerve cells and how they transmit signals in the brain and change over time. This study could lead scientists to a better understanding of how the nervous system develops, is exposed to disease or injury, and the natural rhythms of brain connections are disrupted. Thanks to new imaging technology, scientists are now better able to visualize the circuits that connect the regions and composition of the human brain. 
Advances in techniques, microscopy and computing are enabling scientists to begin mapping the connections between individual nerve cells in animals better than ever before.
By studying intimately the composition of the human brain, scientists can shed light on brain disorders and errors in the development of the neural network, including autism and schizophrenia.
A person is able to sense and perceive the objective world due to the special activity of the brain. It is with the brain that all the senses are connected. Each of these organs reacts to a certain kind of stimuli: the organs of vision - to light exposure, the organs of hearing and touch - to mechanical effects, the organs of taste and smell - to chemical ones. However, the brain itself is not able to perceive these types of influences. He "understands" only electrical signals associated with nerve impulses. In order for the brain to respond to the stimulus, v For each sensory modality, the corresponding physical energy must first be converted into electrical signals, which then follow their own paths to the brain. This translation process is carried out by special cells in the sense organs called receptors. The visual receptors, for example, are located in a thin layer on inside eyes; each visual receptor has Chemical substance that reacts to light, and this reaction triggers a series of events that result in a nerve impulse. The auditory receptors are thin hair cells located deep in the ear; vibrations of the air, which are a sound stimulus, bend these hair cells, as a result of which a nerve impulse arises. Similar processes occur in other sensory modalities.
A receptor is a specialized nerve cell, or neuron; when excited, it sends an electrical signal to intermediate neurons. This signal moves until it reaches its receptive zone in the cerebral cortex, with each sensory modality having its own receptive zone. Somewhere in the brain - maybe in the receptive area of the cortex, or maybe in some other part of the cortex - an electrical signal causes a conscious experience of sensation. So, when we feel a touch, this sensation "happens" in our brain, and not on the skin. In this case, the electrical impulses that directly mediate the sensation of touch were themselves caused by electrical impulses that originated in the receptors of touch, which are located in the skin. Likewise, the bitter taste is not born in the tongue, but in the brain; but the brain impulses that mediate the sense of taste were themselves triggered by electrical impulses from the taste buds of the tongue.
The brain perceives not only the effect of the stimulus, it also perceives a number of characteristics of the stimulus, for example, the intensity of the stimulus. Consequently, the receptors must be able to encode the intensity and quality parameters of the stimulus. How do they do it?
In order to answer this question, scientists had to conduct a series of experiments to register the activity of single receptor cells and pathways during the presentation of various input signals or stimuli to the subject. This way you can determine exactly what properties of the stimulus a particular neuron reacts to. How is such an experiment carried out in practice?
Before the start of the experiment, the animal (monkey) is subjected to a surgical operation, during which thin wires are implanted into certain areas of the visual cortex. Of course, such an operation is performed under sterile conditions and with appropriate anesthesia. Thin wires - microelectrodes - are covered with insulation everywhere, except for the very tip, which records the electrical activity of a neuron in contact with it. After implantation, these microelectrodes do not cause pain, and the monkey can live and move quite normally. During the actual experiment, the monkey is placed in a testing device, and the microelectrodes are connected to amplifying and recording devices. Then the monkey is presented with various visual stimuli. By observing which electrode a stable signal is coming from, it is possible to determine which neuron responds to each of the stimuli. Since these signals are very weak, they must be amplified and displayed on an oscilloscope, which converts them into voltage curves. Most neurons produce a series of nerve impulses that are reflected on the oscilloscope in the form of vertical bursts (spikes). Even in the absence of stimuli, many cells produce infrequent impulses (spontaneous activity). When a stimulus is presented to which a given neuron is sensitive, a rapid sequence of spikes can be seen. By recording the activity of a single cell, scientists have learned a lot about how the senses encode the intensity and quality of a stimulus. The main way of encoding the intensity of a stimulus is the number of nerve impulses per unit of time, i.e. frequency of nerve impulses. Let's show this with the example of touch. If someone touches your hand lightly, a series of electrical impulses will appear in the nerve fibers. If the pressure increases, the magnitude of the impulses remains the same, but their number per unit of time increases. It's the same with other modalities. In general, the higher the intensity, the higher the frequency of the nerve impulses and the greater the perceived intensity of the stimulus.
Stimulus intensity can be encoded in other ways as well. One is to encode the intensity as a temporal pulse-following pattern. At low intensity, nerve impulses follow relatively rarely and the interval between adjacent impulses is variable. At high intensity, however, this interval becomes fairly constant. Another possibility is to encode the intensity as the absolute number of activated neurons: the greater the stimulus intensity, the more neurons involved.
Encoding stimulus quality is more complex. Trying to explain this process, I. Müller in 1825 suggested that the brain is able to distinguish information from different sensory modalities due to the fact that it travels along various sensory nerves (some nerves transmit visual sensations, others - auditory, etc.). Therefore, if we do not take into account a number of Mueller's statements about the unknowability of the real world, we can agree that the neural pathways starting at different receptors end in different areas of the cerebral cortex. Consequently, the brain receives information about the qualitative parameters of the stimulus due to those nerve channels that connect the brain and the receptor. However, the brain is able to distinguish between the effects of one modality. For example, we distinguish red from green or sweet from sour. Apparently, coding here is also associated with specific neurons. For example, there is evidence that a person distinguishes sweet from sour simply because each type of taste has its own nerve fibers. Thus, the "sweet" fibers transmit mainly information from the sweet receptors, along the "sour" fibers - from the sour receptors, and the same is with the "salty" fibers and "bitter" fibers.
However, specificity is not the only possible coding principle. It is also possible that the sensory system uses a specific pattern of nerve impulses to encode quality information. A separate nerve fiber, reacting as much as possible to, say, sweet, can react, but to varying degrees, to other types of gustatory stimuli. One fiber reacts most strongly to sweet, weaker to bitter, and even weaker to salty; so that the "sweet" stimulus would activate a large number of fibers with varying degrees of excitability, and then this particular pattern of neural activity would be the code for the sweet in the system. As a bitter code, a different pattern would be transmitted through the fibers.
At the same time, in the scientific literature, we can find another opinion. For example, there is every reason to assert that the qualitative parameters of a stimulus can be encoded through the form of an electrical signal entering the brain. We encounter a similar phenomenon when we perceive the timbre of a voice or the timbre of a musical instrument. If the signal shape is close to a sinusoid, then the timbre is pleasant to us, but if the shape differs significantly from the sinusoid, then we have a feeling of dissonance.
Thus, the reflection in sensations of the qualitative parameters of the stimulus is a very complex process, the nature of which has not been fully understood.
By: Atkinson RL, Atkinson R.S., Smith E.E. et al. Introduction to Psychology: A Textbook for Universities / Per. from English under. ed. V.P. Zinchenko, - M .: Trivola, 1999.
Feelings connect a person with the outside world and are both the main source of information about him and the main condition for mental development. However, despite the obviousness of these provisions, they have been repeatedly questioned. Representatives of the idealistic trend in philosophy and psychology often expressed the idea that the real source of our conscious activity is not sensations, but the internal state of consciousness, the ability of rational thinking, inherent in nature and not dependent on the influx of information coming from the external world. These views formed the basis of philosophy rationalism. Its essence consisted in the assertion that consciousness and reason are the primary, further inexplicable, property of the human spirit.
Idealist philosophers and many psychologists who are supporters of the idealistic concept have often made attempts to reject the position that a person's sensations connect him with the outside world, and to prove the opposite, paradoxical position that sensations separate a person from the outside world with an insurmountable wall. A similar position was put forward by representatives of subjective idealism (D. Berkeley, D. Hume, E. Mach).
I. Müller, one of the representatives of the dualistic trend in psychology, based on the above-mentioned position of subjective idealism, formulated the theory of "specific energy of the senses." According to this theory, each of the sense organs (eye, ear, skin, tongue) does not reflect the effects of the external world, does not provide information about real processes taking place in the environment, but only receives impulses from external influences that excite their own processes. According to this theory, each sense organ has its own "specific energy", excited by any stimulus coming from the outside world. Thus, it is enough to press on the eye or to act on it with an electric current to get the sensation of light; mechanical or electrical stimulation to the ear is sufficient to produce the sensation of sound. From these provisions, it was concluded that the sense organs do not reflect external influences, but are only excited by them, and a person does not perceive the objective influences of the external world, but only his own subjective states reflecting the activity of his sense organs.
Close was the point of view of H. Helmholtz, who did not reject the fact that sensations arise as a result of the influence of objects on the sense organs, but believed that the mental images arising as a result of this influence have nothing to do with real objects. On this basis, he called sensations "symbols" or "signs" of external phenomena, refusing to recognize them as images, or representations, of these phenomena. He believed that the impact of a certain object on the sensory organ evokes in the mind a "sign" or "symbol" of the influencing object, but not its image. "For a certain similarity with the depicted object is required from the image ... From the sign, however, no similarity is required with that of which it is."
It is easy to see that both of these approaches lead to the following statement: a person cannot perceive the objective world, and the only reality is subjective processes reflecting the activity of his senses, which create subjectively perceived "elements of the world."
Similar conclusions were used as the basis of the theory. solipsism(from lat. solus - one, ipse - himself), which boiled down to the fact that a person can only know himself and has no evidence of the existence of something other than himself.
Representatives of the materialist trend, who consider an objective reflection of the external world possible, are on opposite positions. The study of the evolution of the sense organs convincingly shows that in the process of a long historical development, special perceiving organs (sense organs, or receptors) were formed, which specialized in reflecting special types of objectively existing forms of motion of matter (or types of energy): auditory receptors, reflecting sound vibrations; visual receptors reflecting certain ranges of electromagnetic waves, etc. The study of the evolution of organisms shows that in fact we do not have "specific energies of the senses themselves", but specific organs that objectively reflect different kinds energy. Moreover, the high specialization of various sensory organs is based not only on the structural features of the peripheral part of the analyzer - receptors, but also the highest specialization of neurons that are part of the central nervous apparatus, which receive signals perceived by the peripheral sense organs.
It should be noted that human sensations are a product of historical development, and therefore they are qualitatively different from the sensations of animals. In animals, the development of sensations is entirely limited by their biological, instinctive needs. In many animals, certain types of sensations are striking in their subtlety, however, the manifestation of this finely developed ability of sensation cannot go beyond that circle of objects and their properties that are of direct vital importance for animals of this species. For example, bees are able to distinguish the concentration of sugar in a solution much more subtly than the average person, but this limits the subtlety of their taste sensations. Another example: a lizard, which is able to hear the light rustle of a crawling insect, will not react in any way to a very loud sound of stone on stone.
In humans, the ability to sense is not limited by biological needs. Labor created for him an incomparably wider range of needs than for animals, and in activities aimed at satisfying these needs, human abilities, including the ability to feel, constantly developed. Therefore, a person can feel a much larger number of properties of the objects around him than an animal.
1 This section is based on chapters from the book: Psychology. / Ed. prof. K.N. Kornilov, prof. A.A. Smirnova., Prof. B.M. Teplova. - Ed. 3rd, rev. and add. - M .: Uchpedgiz, 1948.