Transfer of information to the human brain. A method has been invented to transmit information directly through the human brain. Interconnections in simple nervous systems

MAIN CHARACTERISTICS OF THE HUMAN HEARING ANALYZER

Structure and functioning of the human auditory analyzer

All sound information that a person receives from the outside world (it is approximately 25% of the total) is recognized by him using the auditory system.

The auditory system is a kind of receiver of information and consists of the peripheral part and higher parts of the auditory system.

The peripheral part of the auditory system performs the following functions:

- an acoustic antenna that receives, localizes, focuses and amplifies the sound signal;

- microphone;

- frequency and time analyzer;

An analog-to-digital converter that converts an analog signal into binary nerve impulses.

The peripheral auditory system is divided into three parts: the outer, middle, and inner ear.

The outer ear consists of the pinna and the ear canal, which ends in a thin membrane called the eardrum. The outer ears and head are components of an external acoustic antenna that connects (matches) the eardrum to the external sound field. The main functions of the external ears are binaural (spatial) perception, localization of sound sources, and amplification of sound energy, especially in the mid and high frequencies.

Auricle 1 in the area of ​​the outer ear (Fig. 1.a) directs acoustic vibrations into the ear canal 2, ending with the eardrum 5. The auditory canal serves as an acoustic resonator at frequencies of about 2.6 kHz, which increases the sound pressure three times. Therefore, in this frequency range the sound signal is significantly amplified, and it is here that the region of maximum hearing sensitivity is located The sound signal further affects the eardrum3.

The eardrum is a thin film 74 microns thick, shaped like a cone with its tip facing the middle ear. It forms the border with the middle ear region and is connected here to the musculoskeletal lever mechanism in the form of a hammer 4 and incus 5. The pedicle of the incus rests on the membrane of the oval window 6 inner ear 7. The hammer-incus lever system is a transformer of vibrations of the eardrum, increasing the sound pressure on the membrane of the oval window for the greatest return of energy from the air environment of the middle ear, which communicates with the external environment through the nasopharynx 8, into the area of ​​the inner ear 7, filled with incompressible fluid - perilymph.

The middle ear is an air-filled cavity connected to the nasopharynx by the Eustachian tube to equalize atmospheric pressure. The middle ear performs the following functions: matching the impedance of the air environment with the liquid environment of the cochlea of ​​the inner ear; protection from loud sounds (acoustic reflex); amplification (lever mechanism), due to which the sound pressure transmitted to the inner ear is amplified by almost 38 dB compared to that which hits the eardrum.

Fig.1. Structure of the hearing organ

The structure of the inner ear (shown expanded in Fig. 1.6) is very complex and is discussed here schematically. Its cavity 7 is a tube tapering towards the apex, coiled into 2.5 turns in the form of a snail 3.5 cm long, to which are adjacent the channels of the vestibular apparatus in the form of three rings 9. This entire labyrinth is limited by a bony septum 10. Note that in the inlet part of the tube, in addition to the oval membrane, there is a round window membrane 11, performing the auxiliary function of coordinating the middle and inner ear.

The main membrane is located along the entire length of the cochlea 12 - acoustic signal analyzer. It is a narrow ribbon of flexible ligaments (Fig. 1.6), expanding towards the top of the cochlea. The cross section (Fig. 1.c) shows the main membrane 12, bone (Reissner's) membrane 13, separating the liquid environment of the vestibular apparatus from the auditory system; along the main membrane there are layers of endings of nerve fibers of the 14th organ of Corti, connecting into a tourniquet 15.

The main membrane consists of several thousand transverse fibers length 32 mm. The organ of Corti contains specialized auditory receptors- hair cells. In the transverse direction, the organ of Corti consists of one row of inner hair cells and three rows of outer hair cells.

The auditory nerve is a twisted trunk, the core of which consists of fibers extending from the apex of the cochlea, and the outer layers from its lower sections. Having entered the brain stem, neurons interact with cells at various levels, rising to the cortex and crossing along the way so that auditory information from the left ear comes mainly to the right hemisphere, where emotional information is mainly processed, and from the right ear to the left hemisphere, where semantic information is mainly processed. In the cortex, the main hearing zones are located in the temporal region, and there is constant interaction between both hemispheres.

The general mechanism of sound transmission can be simplified as follows: sound waves pass through the sound channel and excite vibrations of the eardrum. These vibrations are transmitted through the ossicular system of the middle ear to the oval window, which pushes fluid into the upper part of the cochlea.

When the membrane of the oval window oscillates in the fluid of the inner ear, elastic vibrations occur, moving along the main membrane from the base of the cochlea to its apex. The structure of the main membrane is similar to a system of resonators with resonant frequencies localized along their length. The membrane areas located at the base of the cochlea resonate to the high-frequency components of sound vibrations, causing them to vibrate, the middle ones react to the mid-frequency ones, and the areas located near the top - to low frequencies. High-frequency components in the lymph quickly attenuate and do not affect areas of the membrane remote from the beginning.

Resonance phenomena localized on the surface of the membrane in the form of a relief, as shown schematically in Fig. 1. G, excite nerve “hair” cells located on the main membrane in several layers, forming the organ of Corti. Each of these cells has up to one hundred “hair” endings. On the outer side of the membrane there are three to five layers of such cells, and under them there is an inner row, so that the total number of “hair” cells interacting with each other layer by layer when the membrane is deformed is about 25 thousand.

In the organ of Corti, mechanical vibrations of the membrane are converted into discrete electrical impulses of nerve fibers. When the main membrane vibrates, the cilia on the hair cells bend, and this generates an electrical potential, which causes a flow of electrical nerve impulses that carry all the necessary information about the received sound signal to the brain for further processing and response. The result of this complex process is the conversion of the input acoustic signal into electrical form, which is then transmitted to the auditory areas of the brain through the auditory nerves.

The higher parts of the auditory system (including the auditory zones of the cortex) can be considered as a logical processor that identifies (decodes) useful sound signals against a background of noise, groups them according to certain characteristics, compares them with images in memory, determines their information value and makes a decision on responses. actions.

Transmission of signals from auditory analyzers to the brain

The process of transmitting nerve stimuli from hair cells to the brain is electrochemical in nature.

The mechanism of transmission of nerve stimuli to the brain is represented by the diagram in Fig. 2, where L and R are the left and right ears, 1 are auditory nerves, 2 and 3 are intermediate centers for the distribution and processing of information located in the brain stem, and 2 are the so-called . cochlear nuclei, 3 - superior olives.

Fig.2. Mechanism of transmission of nerve stimuli to the brain

The mechanism by which the sensation of pitch is formed is still subject to debate. It is only known that at lower frequencies several pulses occur for each half-cycle of sound vibration. At higher frequencies, pulses do not occur in every half-cycle, but less frequently, for example, one pulse every second period, and at higher frequencies even every third. The frequency of nerve impulses arising depends only on the intensity of stimulation, i.e. on the sound pressure level.

Most of the information coming from the left ear is transmitted to the right hemisphere of the brain and, conversely, most of the information coming from the right ear is transmitted to the left hemisphere. In the auditory parts of the brain stem, pitch, sound intensity and some characteristics of timbre are determined, i.e. Primary signal processing is performed. Complex processing processes take place in the cerebral cortex. Many of them are congenital, many are formed in the process of communication with nature and people, starting from infancy.

It has been established that in most people (95% of right-handers and 70% of left-handers) the left hemisphere is allocated and processed; semantic signs of information, and on the right - aesthetic ones. This conclusion was obtained in experiments on the biotic (bifurcated, separate) perception of speech and music. When listening with the left ear to one set of numbers and the right ear to another, the listener gives preference to the one that is perceived by the right ear and information about which is received by the left hemisphere. On the contrary, when listening to different melodies with different ears, preference is given to the one that is listened to by the left ear and the information from which enters the right hemisphere.

Nerve endings under the influence of excitation generate impulses (i.e., practically a signal already encoded, almost digital), transmitted along nerve fibers to the brain: at the first moment up to 1000 impulses/s, and after a second - no more than 200 due to fatigue, which determines adaptation process, i.e. decrease in perceived loudness with prolonged exposure to a signal.

A team of scientists from Spain, France and England announced the completion of the first ever experiment on transmitting a signal between the minds of two people using exclusively non-invasive technologies. A signal consisting of 140 bits of information was transmitted from India to France via the Internet. The work was published in PLOS One.

General scheme of the experiment. Image: PLOS one article

The experiment was based on brain-computer interfaces (BCI) and computer-brain interfaces (CBI), the signal was transmitted via the Internet. The message was ultimately the word "hola" - "hello" in Spanish (and Catalan). The Bacon cipher, which uses 5 bits per letter, was used for encoding. The word was transmitted 7 times to collect sufficient statistics, so the final message was 140 bits long.

The scientists modeled the brain-computer interface as follows: to encode “0,” the human “transmitter” moved his foot, and to encode “1,” he moved his palm. By taking an electroencephalogram from the areas of the cerebral cortex responsible for these movements, the computer received the transmitted message in the form of binary bits.

With the computer-brain interface, things were more complicated. On the head of the human “receiver” they found the visual center of the cerebral cortex, upon stimulation of which the phenomenon of phosphenes arose - visual sensations that arise without information from the eye. The presence of such a feeling was coded “1”, the absence - “0”.

Four volunteers aged 28-50 years acted as transmitters and receivers. For the final experiment, the signal was transmitted from India to France. In order to eliminate interference from the senses, the “receiver” person was wearing a light-proof mask over his eyes, and plugs were placed in his ears. To eliminate the possibility of guessing the encoded word, the sequence was first further encoded to obtain a pseudo-random code, which, after transmission, was decrypted to restore the original message.

As a result of the experiment, it was possible to transmit 140 bits of information with an error rate of 4%. For comparison, to make sure that this result is statistically significant: the probability of guessing all 140 characters in a row is less than 10 -22 , and to guess at least 80% of 140 characters is less than 10 -13 . Thus, according to scientists, there actually was a direct transmission of the signal from brain to brain.

The novelty and significance of this work stem from the fact that so far all such experiments have either been limited to one of two interfaces, or have been carried out on laboratory animals, or have involved invasive procedures for implanting sensors into a living organism. In this work, scientists for the first time managed to realize non-invasive transmission from person to person.

The composition of the human brain includes structural and functionally interconnected neurons. This organ of mammals, depending on the species, contains from 100 million to 100 billion neurons.

Each mammalian neuron consists of a cell - an elementary structural unit, dendrites (short process) and an axon (long process). The body of the elementary structural unit contains the nucleus and cytoplasm.

Axon exits the cell body and often gives rise to many small branches before reaching the nerve endings.

Dendrites extend from the nerve cell body and receive messages from other units of the nervous system.

Synapses– these are 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 entire body, although its mass is only 2% of body weight.

How signals are transmitted in the brain

When the 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 complex.

Many axons are covered in a multilayer myelin sheath, which speeds the transmission of electrical signals along the axon. This shell is formed with the help of specialized elementary structural units of glia. In the central nervous system, glia are called oligodendrocytes, and in the peripheral nervous system they are called Schwann cells. The medulla contains at least ten times more glia than nervous system units. Glia perform many functions. The importance of glia in the transport of nutrients to neurons, cleansing, processing of some dead neurons.

To transmit signals, the functional units of any mammal's body system do not work alone. In a neural circuit, the activity of one elementary unit directly affects many others. To understand how these interactions control 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, becomes susceptible to disease or injury, and disrupts the natural rhythms of brain connections. Thanks to new imaging technology, scientists are now better able to visualize the circuits connecting the regions and composition of the human brain.

Advances in techniques, microscopy and computing technology are allowing scientists to begin to map the connections between individual nerve cells in animals better than ever before.

By studying the composition of the human brain in detail, scientists can shed light on brain disorders and errors in the development of the nervous network, including autism and schizophrenia.

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 go to the opposite hemisphere of the brain, the remaining half goes to the same (ipsilateral) hemisphere. The first switching of optic nerve fibers occurs in the lateral geniculate body of the thalamus. From here, new fibers are sent through the brain to the visual cortex (Fig. 5.17).

Compared to 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 top four are small cell, the bottom two are large cell, so the top layers are called parvocellular(parvo - small, cellula - cell, lat.) and the lower ones - magnocellular(magnus - big, 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 a 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 chiasm; 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 in the posterior hemispheres pass through the lateral geniculate body. A cross-section of this subcortical structure reveals six cell layers, two of which correspond to magnocellular connections (M), and four to parvocellular connections (P) (Zeki, 1992).

There are differences, of which the most significant is the much more pronounced ability of the periphery of the receptive field of the cells of the geniculate body to suppress the effect of the center, i.e. they are more specialized (Hubel, 1974).

Neurons of the lateral geniculate body 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 geniculate bodies of the thalamus (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 shape, movement and depth of visual space. The parvocellular system is involved in visual functions developed in primates, such as color perception and fine detail detection (Merigan, 1989).

The connection between the geniculate bodies and the striate 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-

localization of 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 eventually spreads to all layers. Cells of the third and fifth layers of the cortex send their axons to deeper structures of the brain. Most of the connections between the cells of the striate cortex run perpendicular to the surface, the lateral connections are predominantly short. This suggests the presence of locality in information processing in this area.

The area of ​​the retina that affects the 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 a perfect circle. In a typical case, the receptive field consists of a very long and narrow “op” area, which is adjacent on both sides by wider “o!G” areas (Hubel, 1974).