Feeling the perception of their features in legal activities. Feeling and Perception

Electroencephalography is a method of recording bio electrical phenomena brain. For the first time, biocurrents of the brain were registered on animals, while the skull was opened and electrodes were placed on the cortical substance. This method is called "electrocorticography". Currently, there is a technical possibility of recording electrical phenomena of the brain (biocurrents) from the surface of the head.

Two methods of recording electroencephalography are used: unipolar, in which one passive electrode is placed on the earlobe, and one is active, and the bipolar method, where both electrodes are active, located at a certain distance from each other.

The curve obtained as a result of registration is called an electroencephalogram, on which you can see the main waves of electrical activity, or rhythms of the brain.

1. α-rhythm - a constant sinusoidal rhythm - is recorded from all parts of the brain, but is most characteristic of the parietal and occipital regions. Frequency from - 8 to 14 oscillations per second with an amplitude of 20 to 80 microvolts. This rhythm is recorded in a state of physical and mental rest.

Features of the α-rhythm, its constant characteristic: easily subject to depression, for its disappearance it is enough to open your eyes, characterized by high ability to adaptation - is restored when open eyes at rest.

2. β-rhythm. Allocate high-frequency and low-frequency β-rhythm. Frequency - 14-35 oscillations per minute, amplitude - 10-30 microvolts. It is recorded from all parts of the brain, but is most characteristic of the frontal lobe, during the transition from a state of rest to a state of activity (for example, when opening the eyes).

3. δ-rhythm - is registered in adults in a state deep sleep, and in children - during physical and mental activity. The frequency of this rhythm is small - 0.5-3 oscillations per second, the amplitude is 250-1000 microvolts.

4. θ-rhythm - small, with a frequency of 4-7 oscillations per second, has a high amplitude - 100-150 microvolts. It is registered in the process of REM sleep, during brain hypoxia in adults, and in adolescents - in a state of activity.

In the study, techniques are used to obtain certain rhythms. The desynchronization reaction is the replacement of the α-rhythm by the β-rhythm. When the eyes are opened, the flow of impulses to the cerebral cortex through the reticular formation increases, and the predominance of excitation processes in the cortex is observed. Evoked potentials are high-amplitude, they are recorded when exposed to specific stimuli in strictly defined parts of the brain. For example, flashes of high-amplitude potentials are recorded in the occipital region when stimulated by light.

riddles in human body a lot, and not all are still subject to doctors. The most complex and confusing of them, perhaps, is the brain. Various methods of brain research, such as electroencephalography, help doctors lift the veil of secrecy. What is it and what can the patient expect from the procedure?

Who is eligible for an electroencephalography test?

Electroencephalography (EEG) allows you to clarify many diagnoses associated with infections, injuries and brain disorders.

The doctor may refer you for an examination if:

There is a possibility of epilepsy. The brain waves in this case show a special epileptiform activity, which is expressed in the modified form of the graphs.
It is required to establish the exact location of the injured part of the brain or tumor.
There are some genetic diseases.
There are serious violations of sleep and wakefulness.
The work of the vessels of the brain is disrupted.
An assessment of the effectiveness of the treatment is needed.

The electroencephalography method is applicable to both adults and children, it is non-traumatic and painless. A clear picture of the work of brain neurons in its different parts makes it possible to clarify the nature and causes of neurological disorders.

Method of brain research electroencephalography - what is it?

Such an examination is based on the registration of bioelectric waves emitted by the neurons of the cerebral cortex. With the help of electrodes, activity nerve cells is captured, amplified and converted into a graphical form by the device.

The resulting curve characterizes the process of work of different parts of the brain, its functional state. IN normal condition it has a certain shape, and deviations are diagnosed taking into account changes in the appearance of the graph.

EEG can be performed in various options. The room for him is isolated from extraneous sounds and light. The procedure usually takes 2-4 hours and is performed in a clinic or laboratory. In some cases, electroencephalography with sleep deprivation requires more time.

The method allows doctors to obtain objective data about the state of the brain, even when the patient is unconscious.

How is an EEG performed?

If a doctor prescribes electroencephalography, what is it for the patient? He will be asked to sit in comfortable position or lie down, put on a helmet fixing the electrodes made of elastic material. If the recording is supposed to be long, then a special conductive paste or collodion is applied at the points of contact of the electrodes with the skin. The electrodes do not cause any discomfort.

EEG does not suggest any violation of the integrity of the skin or the introduction medicines(premedication).

Routine recording of brain activity occurs for a patient in a state of passive wakefulness, when he lies quietly or sits with his eyes closed. It's quite difficult, time drags on slowly and you have to fight sleep. The laboratory assistant periodically checks the patient's condition, asks to open his eyes and perform certain tasks.

During the study, the patient should minimize any motor activity that would interfere. It’s good if the laboratory manages to fix the doctors of interest neurological manifestations(convulsions, tics, epileptic seizure). Sometimes an attack in epileptics is provoked purposefully in order to understand its type and origin.

Preparation for the EEG

On the eve of the study, it is worth washing your hair. It is better not to braid your hair and not to use any styling products. Leave hairpins and clips at home, but long hair collect in the tail, if required.

Metal jewelry should also be left at home: earrings, chains, lip and eyebrow piercings. Before entering the office, disable mobile phone(not only sound, but completely), so as not to interfere with sensitive sensors.

Before the examination, you need to eat so as not to feel hungry. It is advisable to avoid any unrest and strong feelings, but take any sedatives do not do it.

You may need a tissue or towel to wipe off any remaining fixative gel.

Samples during the EEG

In order to track the response of brain neurons in different situation, and expand the demonstrative capabilities of the method, the electroencephalography examination includes several tests:

1. Eye opening-closing test. The laboratory assistant makes sure that the patient is conscious, hears him, and follows the instructions. The absence of patterns on the chart at the time of opening the eyes indicates pathology.

2. Test with photostimulation, when flashes of bright light are directed into the eyes of the patient during recording. Thus, epileptimorphic activity is revealed.

3. A test with hyperventilation, when the subject breathes deeply voluntarily for several minutes. Frequency respiratory movements at this time, the oxygen content in the blood decreases slightly, but the oxygen content in the blood rises and, accordingly, the supply of oxygenated blood to the brain increases.

4. Sleep deprivation, when the patient is immersed in a short sleep with the help of sedatives or remains in the hospital for daily observation. This allows you to obtain important data on the activity of neurons at the time of awakening and falling asleep.

5. Stimulation mental activity is to solve simple problems.

6. Stimulation of manual activity, when the patient is asked to perform a task with an object in his hands.

All this gives more complete picture the functional state of the brain and notice violations that have a slight external manifestation.

The duration of the electroencephalogram

The time of the procedure may vary depending on the goals set by the doctor and the conditions of a particular laboratory:

30 minutes or more if you can quickly register the activity you are looking for;
2-4 hours in the standard version, when the patient is examined reclining in a chair;
6 or more hours on EEG with daytime sleep deprivation;
12-24 hours, when all phases of night sleep are examined.

The scheduled time of the procedure can be changed at the discretion of the doctor and laboratory assistant in any direction, because if there are no characteristic patterns corresponding to the diagnosis, the EEG will have to be repeated, spending extra time and money. And if all the necessary records are obtained, there is no point in tormenting the patient with forced inaction.

What is video monitoring during an EEG?

Sometimes the electroencephalography of the brain is duplicated by a video recording, which records everything that happens during the study with the patient.

Video monitoring is prescribed for patients with epilepsy to correlate how behavior during an attack correlates with brain activity. Timed matching of characteristic waves with the picture can clarify gaps in the diagnosis and help the clinician understand the condition of the subject for more accurate treatment.

The result of electroencephalography

When the patient underwent electroencephalography, the conclusion is handed out along with printouts of all graphs of the wave activity of various parts of the brain. In addition, if video monitoring was also carried out, the recording is saved on a disk or flash drive.

At a consultation with a neurologist, it is better to show all the results so that the doctor can assess the features of the patient's condition. Electroencephalography of the brain is not the basis for the diagnosis, but significantly clarifies the picture of the disease.

To ensure that all the smallest teeth are clearly visible on the graphs, it is recommended to store the printouts flattened in a hard folder.

Encryption from the brain: types of rhythms

When an electroencephalography is passed, which each graph shows, it is extremely difficult to understand on your own. The doctor will make a diagnosis based on the study of changes in the activity of areas of the brain during the study. But if the EEG was prescribed, then the reasons were good, and it would not hurt to consciously approach your results.

So, we have in our hands a printout of such an examination, like electroencephalography. What are these - rhythms and frequencies - and how to determine the limits of the norm? The main indicators that appear in the conclusion:

1. Alpha rhythm. The frequency normally ranges from 8-14 Hz. Between the cerebral hemispheres, a difference of up to 100 μV can be observed. The pathology of the alpha rhythm is characterized by asymmetry between the hemispheres exceeding 30%, the amplitude index is above 90 μV and below 20.

2. Beta rhythm. It is mainly fixed on the anterior leads (in frontal lobes). For most people, a typical frequency is 18-25 Hz with an amplitude of no more than 10 μV. The pathology is indicated by an increase in amplitude over 25 μV and a persistent spread of beta activity to the posterior leads.

3. Delta rhythm and Theta rhythm. Fixed only during sleep. The appearance of these activities during the period of wakefulness signals a malnutrition of the brain tissues.

5. Bioelectric activity (BEA). Normal demonstrates synchrony, rhythm, absence of paroxysms. Deviations are manifested in early epilepsy childhood, predisposition to convulsions and depression.

In order for the results of the study to be indicative and informative, it is important to follow the prescribed treatment regimen exactly, without canceling the drugs before the study. Alcohol or energy drinks taken the day before can distort the picture.

What is electroencephalography used for?

For the patient, the benefits of the study are obvious. The doctor can check the correctness of the prescribed therapy and change it if necessary.

In people with epilepsy, when a period of remission is established by observation, the EEG may show seizures that are not superficially observable and still require medical intervention. Or avoid unreasonable social restrictions, specifying the features of the course of the disease.

The study can also contribute to the early diagnosis of neoplasms, vascular pathologies, inflammation and degeneration of the brain.

The introduction of this method into clinical practice and experimental neurophysiology made it possible to obtain fundamentally new data on the functional organization of the brain: on the so-called non-specific systems ah - activating and deactivating (synchronizing), about the organization of sleep (slow and fast sleep) and the role of dysfunction of non-specific systems in many pathological processes.

The method of electroencephalography has played a major role in the development of modern ideas about the pathogenesis of epilepsy. For diagnosis, the latter is the most important method instrumental research.

For EEG registration special devices are used - electroencephalographs, which amplify by hundreds of thousands, a million times the bioelectric activity removed from the brain and register it on a paper tape or in a computer processor with subsequent visual or automatic analysis.

Electroencephalography is recorded in a relaxed state of the subject, with his eyes closed.

EEG with functional tests

After recording background activity, apply functional tests: short-term opening of the eyes (causes an activation reaction - the disappearance of the a-rhythm), light rhythmic stimulation (normally, the assimilation of frequencies of light flickers in the range of 6-18 Hz is noted); hyperventilation - deep breathing ("inflating the ball") - causes synchronization, i.e. slowing down the frequency of oscillations and increasing their amplitude. This phenomenon is especially pronounced in children and usually becomes insignificant after the age of 20.

Evoked Potentials

special method electroencephalographic study is a method of recording evoked responses of the brain (evoked potentials - EP) to discrete stimulation (light, sound, etc.), EEG registers a regular response, however, when the usual way registration, the insignificant amplitude of the response against the background of the rhythmic activity of a huge mass of neurons does not allow one to distinguish the response. The creation of special devices that allow summing repeated responses and leveling background activity made it possible to introduce the method of evoked potentials into clinical and experimental practice.

The evoked potentials are rhythmic fluctuations, in which early and late components are distinguished (Fig. 1.9.14). It is believed that the early components reflect the processes associated with the excitation and passage of an impulse along the corresponding sensory path with its switching in relay structures; late components are associated with afferent from non-specific structures activated by specific impulses.

There are negative (directed upwards from the isoline) and positive (directed downwards) oscillations, which are marked with the corresponding numbers or numbers indicating the latent periods of oscillations in milliseconds.

Investigate responses to flashes of light - visual evoked potentials (VEP, sound clicks - auditory evoked potentials (AEP) and electrical stimulation peripheral nerves or receptors - somatosensory evoked potentials (SSEPs).

IN clinical practice the method of evoked potentials is used in diagnosing the level and localization of damage to the nervous system and, accordingly, certain diseases, in particular multiple sclerosis (the early components of VEP are disturbed), hysterical blindness (VEP do not change), etc.

IN last years new methods of computer processing of electroencephalography have entered clinical practice: amplitude mapping, spectral power estimation, multi-step dipole localization method, low-resolution electromagnetic tomography method.

Amplitude mapping of bioelectrical activity of the brain

This method allows you to visualize the distribution of potential differences on the surface of the brain at any time, evaluate the polarity, spatial distribution of certain phenomena, as well as the correspondence of potential maps to the dipole model (namely, the presence of 1 or 2 extrema of the opposite sign) .

Spectral Power Estimation

With help this method the analysis of the spatial distribution of the spectral power according to the main EEC rhythms: α, β 1 , β 2 , θ and δ is carried out on the given artifact-free sections of the records (analysis epochs). The choice of epochs is determined by the presence of phenomena of interest to the researcher on the EEG.

Multi-step dipole localization method

Based on the analysis of the distribution of potential differences on the surface of the head, the BranLoc program makes it possible to solve the inverse EEG problem, i.e., to determine the three-dimensional localization of the sources of bioelectrical activity of the brain. The source of activity is represented as a dipole in three-dimensional space (Cartesian coordinate system), where the X axis passes along the inion-nason line, the Y axis is parallel to the line connecting ear canals, the Z axis is from the basis to the artex. The program features allow you to display the results of dipole localization on real and standardized CT or MRI slices.

EEG norm

Bioelectric potentials are normally characterized by symmetry. EEG reflects the total functional activity of neurons in the cerebral cortex. However, this activity is under the influence of non-specific stem-cortical systems, activating and deactivating, is rhythmically organized and has a different age characteristic.

On the electroencephalography of an awake adult (Fig. 1.9.10), bioelectric activity consists mainly of rhythm and weighty vili with a frequency of 8-12 Hz and an amplitude of 50-100 μV (a-rhythm), mainly expressed in the posterior parts of the brain, maximum - in occipital leads, and from more frequent fluctuations in the anterior parts of the brain with a frequency of 13-40 Hz and an amplitude of up to 15 μV (p-rhythm). material from the site

child's EEG

The EEG of the newborn is characterized by the absence of rhythmic activity. Irregular slow waves are registered. By the age of 3 months, rhythmic activity is formed, mainly in the 5-range. By 6 months, the 0-rhythm (5-6 Hz) dominates. In the future, the so-called slow a-rhythm (7-8 Hz) appears and grows, which becomes dominant by the age of 12 months.

The development of electronics in the 20s of our century - the creation of sensitive triodes used in the construction of amplifiers, oscilloscope tubes for observing signals - was the technical basis of electroencephalography. In 1928, the German psychiatrist Berger, using a special apparatus - electroencephalograph- recorded in clinical setting electrical brain signals. The basic principle of the electroencephalograph is quite simple. Electrodes that pick up the minimal signals resulting from electrical fluctuations in the brain are attached to the head. These oscillations can appear in any parts of the brain, however, in the channel of the amplifier connected to this pair of electrodes, the rhythms of the areas closest to the electrodes are best expressed. To record and further analyze these extremely small signals, they had to be amplified by several million times.

Electroencephalography of the brain is a record of the total electrical activity of a large number of brain cells. The EEG of an adult healthy person in the waking state is a continuous curve consisting of many rhythmic (frequency) components: alpha rhythm with a frequency of 8-13 Hz, beta rhythm - 13-30 Hz, gamma rhythm - 30-70 Hz, delta rhythm - 1-3 Hz.

The degree of violation of brain biopotentials quite accurately characterizes the overall severity of the disease. For example, in patients with frequent epileptic seizures EEG in the interictal period is usually more pronounced than in patients with rare seizures. In diseases associated with impaired consciousness, EEG changes more roughly expressed in a state of coma than in a state of stupor. Most successful electroencephalography of the brain used for localization pathological process. Further progress in clinical electroencephalography is associated with overcoming the gap that exists between the amount of information embedded in the received signals and the very imperfect ways of deciphering this information (what is what?). This gap may be overcome if the ideas and methods of theoretical cybernetics are applied to the analysis of bioelectrical activity. brain signals.

Using electro magnetic fields generated by the brain, capturing and registering them in the form of electroencephalograms, electronics thereby transmits information about the processes to various departments nervous system- "from the source", being a direct, and often the only means of obtaining such information. Electroencephalography are successfully used in the study of not only the onto- and phylogenesis of the brain, but also to reveal the mechanisms of the closure of conditioned reflex connections, the action narcotic substances, to analyze the formation and interaction functional systems brain, providing the performance of higher mental functions, for the study and diagnosis of lesions of the central nervous system in clinical conditions and for many other purposes.

Methods for studying the work of the brain

TOPIC 2. METHODS OF PSYCHOPHYSIOLOGY

2.1. Methods for studying the work of the brain
2.2. Electrical activity of the skin
2.3. Performance indicators of cardio-vascular system
2.4. Activity metrics muscular system
2.5. Activity metrics respiratory system
2.6. Eye reactions
2.7. Lie detector
2.8. Choice of methods and indicators

This section will present the systematics, methods of registration and the significance of physiological indicators associated with human mental activity. Psychophysiology is an experimental discipline, therefore the interpretive possibilities of psychophysiological research are largely determined by the perfection and variety of the methods used. Right choice methodology, the adequate use of its indicators and the interpretation of the results obtained corresponding to the resolving capabilities of the methodology are the conditions necessary for a successful psychophysiological study.

2.1.1. Electroencephalography
2.1.2. evoked potentials of the brain
2.1.3. Topographic mapping of electrical activity of the brain (TCEAM)
2.1.4. Computed tomography (CT)
2.1.5. neuronal activity
2.1.6. Methods of influencing the brain

The central place in a number of methods of psychophysiological research is occupied by various ways recording the electrical activity of the central nervous system, and primarily the brain.

Electroencephalography- method of registration and analysis of the electroencephalogram (EEG), i.e. total bioelectrical activity taken both from the scalp and from the deep structures of the brain. The last at the person is possible only in clinical conditions.
In 1929, the Austrian psychiatrist H. Berger discovered that "brain waves" could be recorded from the surface of the skull. He established that electrical characteristics these signals depend on the condition of the subject. The most noticeable were synchronous waves of relatively large amplitude with a characteristic frequency of about 10 cycles per second. Berger called them alpha waves and contrasted them with the high-frequency "beta waves" that occur when a person goes into a more active state. Berger's discovery led to the creation of an electroencephalographic method for studying the brain, which consists in recording, analyzing and interpreting the biocurrents of the brain of animals and humans.
One of the most striking features of the EEG is its spontaneous, autonomous nature. Regular electrical activity of the brain can be recorded already in the fetus (that is, before the birth of the organism) and stops only with the onset of death. Even with deep coma and anesthesia there is a special characteristic picture brain waves.
Today, the EEG is the most promising, but still the least deciphered source of data for the psychophysiologist.

Registration conditions and methods of EEG analysis. The stationary complex for recording EEG and a number of other physiological parameters includes a soundproof shielded chamber, an equipped place for the test subject, monochannel amplifiers, recording equipment (ink encephalograph, multichannel tape recorder). Usually, from 8 to 16 EEG recording channels are used simultaneously from different parts of the skull surface. EEG analysis is carried out both visually and with the help of a computer. In the latter case, special software is required.

According to the frequency in the EEG, the following types of rhythmic components are distinguished:

delta rhythm (0.5-4 Hz);
theta rhythm (5-7 Hz);
alpha rhythm(8-13 Hz) - the main rhythm of the EEG, prevailing at rest;
mu-rhythm - in terms of frequency-amplitude characteristics, it is similar to the alpha rhythm, but prevails in the anterior sections of the cerebral cortex;
beta rhythm (15-35 Hz);
gamma rhythm (above 35 Hz).

It should be emphasized that such a division into groups is more or less arbitrary; it does not correspond to any physiological categories. Slower frequencies of electrical potentials of the brain were also registered up to periods of the order of several hours and days. Recording at these frequencies is performed using a computer.

Basic rhythms and parameters of the encephalogram. 1. Alpha wave - a single two-phase oscillation of the potential difference with a duration of 75-125 ms., It approaches a sinusoidal in shape. 2. Alpha rhythm - rhythmic fluctuation of potentials with a frequency of 8-13 Hz, expressed more often in back departments brain with closed eyes in a state of relative rest, the average amplitude is 30-40 μV, usually modulated into spindles. 3. Beta wave - a single two-phase oscillation of potentials with a duration of less than 75 ms. and an amplitude of 10-15 μV (no more than 30). 4. Beta rhythm - rhythmic oscillation of potentials with a frequency of 14-35 Hz. It is better expressed in the fronto-central areas of the brain. 5. Delta wave - a single two-phase oscillation of the potential difference with a duration of more than 250 ms. 6. Delta rhythm - rhythmic oscillation of potentials with a frequency of 1-3 Hz and an amplitude of 10 to 250 μV or more. 7. Theta wave - a single, more often two-phase oscillation of the potential difference with a duration of 130-250 ms. 8. Theta rhythm - rhythmic oscillation of potentials with a frequency of 4-7 Hz, more often bilateral synchronous, with an amplitude of 100-200 μV, sometimes with spindle-shaped modulation, especially in the frontal region of the brain.

Another important characteristic of the electrical potentials of the brain is the amplitude, i.e. the amount of fluctuation. The amplitude and frequency of oscillations are related to each other. The amplitude of high-frequency beta waves in the same person can be almost 10 times lower than the amplitude of slower alpha waves.
Importance when recording, the EEG has the location of the electrodes, while the electrical activity simultaneously recorded from different points of the head can vary greatly. When recording EEG, two main methods are used: bipolar and monopolar. In the first case, both electrodes are placed in the electrically active points of the scalp, in the second case, one of the electrodes is located at a point that is conventionally considered electrically neutral (earlobe, bridge of the nose). With bipolar recording, an EEG is recorded, representing the result of the interaction of two electrically active points (for example, frontal and occipital leads), with monopolar recording, the activity of a single lead relative to an electrically neutral point (for example, frontal or occipital leads relative to the earlobe). The choice of one or another recording option depends on the objectives of the study. In research practice, the monopolar variant of registration is more widely used, since it makes it possible to study the isolated contribution of one or another area of the brain to the process being studied.
The International Federation of Societies for Electroencephalography has adopted the so-called "10-20" system to accurately indicate the location of the electrodes. In accordance with this system, the distance between the middle of the bridge of the nose (nasion) and the hard bony tubercle on the back of the head (inion), as well as between the left and right ear fossae, is accurately measured in each subject. The possible locations of the electrodes are separated by intervals of 10% or 20% of these distances on the skull. At the same time, for the convenience of registration, the entire skull is divided into regions indicated by the letters: F - frontal, O - occipital region, P - parietal, T - temporal, C - region of the central sulcus. Odd numbers of abduction sites refer to the left hemisphere, and even numbers to the right hemisphere. The letter Z - denotes the assignment from the top of the skull. This place is called the vertex and is used especially often (see Reader 2.2).

Clinical and static methods for studying EEG. From the moment of its inception, two approaches to EEG analysis: visual (clinical) and statistical.
Visual (clinical) EEG analysis usually used in diagnostic purposes. The electrophysiologist, relying on certain methods of such an analysis of the EEG, solves the following questions: does the EEG correspond to generally accepted standards of the norm; if not, what is the degree of deviation from the norm, does the patient show signs focal lesion brain and what is the localization of the lesion. Clinical Analysis EEG is always strictly individual and is predominantly qualitative. Despite the fact that there are generally accepted methods for describing the EEG in the clinic, clinical interpretation The EEG largely depends on the experience of the electrophysiologist, his ability to "read" the electroencephalogram, highlighting the hidden and often very variable pathological signs.
However, it should be emphasized that gross macrofocal disturbances or other distinct forms of EEG pathology are rare in wide clinical practice. Most often (70-80% of cases), there are diffuse changes in the bioelectrical activity of the brain with symptoms that are difficult to formally describe. Meanwhile, it is precisely this symptomatology that may be of particular interest for the analysis of the contingent of subjects who belong to the group of so-called "minor" psychiatry - conditions bordering between a "good" norm and obvious pathology. It is for this reason that now there are special efforts on formalization and even development of computer programs for the analysis of clinical EEG.
Statistical research methods electroencephalograms come from the fact that the background EEG is stationary and stable. Further processing in the overwhelming majority of cases is based on the Fourier transform, the meaning of which is that a wave of any complex shape is mathematically identical to the sum of sinusoidal waves of different amplitudes and frequencies.
The Fourier transform allows you to transform the wave pattern background EEG to frequency and set the power distribution for each frequency component. Using the Fourier transform, the most complex EEG oscillations can be reduced to a series of sinusoidal waves with different amplitudes and frequencies. On this basis, new indicators are distinguished that expand the meaningful interpretation of the rhythmic organization of bioelectric processes.
For example, a special task is to analyze the contribution, or relative power, of different frequencies, which depends on the amplitudes of the sinusoidal components. It is solved by constructing power spectra. The latter is a set of all power values of EEG rhythmic components calculated with a certain discretization step (in the amount of tenths of a hertz). Spectra can characterize the absolute power of each rhythmic component or relative, i.e. the severity of the power of each component (in percent) in relation to the total power of the EEG in the analyzed segment of the record.

EEG power spectra can be subjected to further processing, for example, correlation analysis, while auto- and cross-correlation functions are calculated, as well as coherence , which characterizes the measure of synchronicity frequency bands EEG in two different leads. Coherence ranges from +1 (completely matching waveforms) to 0 (absolutely matching waveforms). various forms waves). Such an assessment is carried out at each point of the continuous frequency spectrum or as an average within the frequency subbands.
Using the calculation of coherence, it is possible to determine the nature of intra- and interhemispheric relations EEG indicators at rest and during various activities. In particular, using this method, it is possible to establish the leading hemisphere for a particular activity of the subject, the presence of stable interhemispheric asymmetry, etc. Due to this, the spectral-correlation method for assessing the spectral power (density) of EEG rhythmic components and their coherence is currently one of the most common.

Sources of EEG generation. Paradoxically, but the actual impulse activity neurons is not reflected in the fluctuations of the electrical potential recorded from the surface of the human skull. The reason is that the impulse activity of neurons is not comparable with the EEG in terms of time parameters. The duration of the impulse (action potential) of the neuron is no more than 2 ms. The time parameters of the rhythmic components of the EEG are calculated in tens and hundreds of milliseconds.
It is generally accepted that electrical processes recorded from the surface of an open brain or scalp reflect synaptic neuron activity. We are talking about potentials that arise in the postsynaptic membrane of a neuron that receives an impulse. Excitatory postsynaptic potentials have a duration of more than 30 ms, and inhibitory postsynaptic potentials of the cortex can reach 70 ms or more. These potentials (in contrast to the action potential of a neuron, which arises according to the "all or nothing" principle) are gradual in nature and can be summed up.
Simplifying the picture somewhat, we can say that positive potential fluctuations on the surface of the cortex are associated either with excitatory postsynaptic potentials in its deep layers, or with inhibitory postsynaptic potentials in surface layers. Negative potential fluctuations on the surface of the crust presumably reflect the opposite ratio of sources of electrical activity.
The rhythmic nature of the bioelectric activity of the cortex, and in particular the alpha rhythm, is mainly due to the influence of subcortical structures, primarily the thalamus ( diencephalon). It is in the thalamus that the main, but not the only, pacemakers or pacemakers. Unilateral removal of the thalamus or its surgical isolation from the neocortex leads to the complete disappearance of the alpha rhythm in the areas of the cortex of the operated hemisphere. At the same time, nothing changes in the rhythmic activity of the thalamus itself. The neurons of the nonspecific thalamus have the property of authoritativeness. These neurons, through appropriate excitatory and inhibitory connections, are able to generate and maintain rhythmic activity in the cerebral cortex. An important role in the dynamics of the electrical activity of the thalamus and cortex is played by reticular formation brain stem. It can have a synchronizing effect, i.e. contributing to the generation of a steady rhythmic pattern, and dissynchronizing, violating the coordinated rhythmic activity (see Reader 2.3).

Synaptic activity of neurons

The functional significance of the ECG and its components. The question of the functional significance of individual components of the EEG is of great importance. Most Attention researchers have always been attracted here alpha rhythm is the dominant resting EEG rhythm in humans.
There are many assumptions regarding the functional role of the alpha rhythm. The founder of cybernetics N. Wiener and after him a number of other researchers believed that this rhythm performs the function of temporal scanning ("reading") of information and is closely related to the mechanisms of perception and memory. It is assumed that the alpha rhythm reflects the reverberation of excitations that encode intracerebral information and create an optimal background for the process of receiving and processing. afferent signals. Its role consists in a kind of functional stabilization of the states of the brain and ensuring readiness to respond. It is also assumed that the alpha rhythm is associated with the action of brain selective mechanisms that act as a resonant filter and thus regulate the flow of sensory impulses.
At rest, other rhythmic components may be present in the EEG, but their significance is best clarified when the functional states of the body change ( Danilova, 1992). So, the delta rhythm in a healthy adult at rest is practically absent, but it dominates the EEG at the fourth stage of sleep, which got its name from this rhythm (slow-wave sleep or delta sleep). On the contrary, the theta rhythm is closely associated with emotional and mental stress. It is sometimes referred to as the stress rhythm or tension rhythm. In humans, one of the EEG symptoms emotional arousal is the amplification of the theta rhythm with an oscillation frequency of 4-7 Hz, which accompanies the experience of both positive and negative emotions. When performing mental tasks, both delta and theta activity may increase. Moreover, the strengthening of the last component is positively correlated with the success of solving problems. In its origin, the theta rhythm is associated with cortico-limbic interaction. It is assumed that the increase in theta rhythm during emotions reflects the activation of the cerebral cortex from the limbic system.
The transition from a state of rest to tension is always accompanied by a desynchronization reaction, the main component of which is high-frequency beta activity. Mental activity in adults is accompanied by an increase in the power of the beta rhythm, and a significant increase in high-frequency activity is observed during mental activity that includes elements of novelty, while stereotypical, repetitive mental operations are accompanied by its decrease. It has also been established that the success of performing verbal tasks and tests for visual-spatial relations is positively associated with high activity EEG beta range of the left hemisphere. According to some assumptions, this activity is associated with a reflection of the activity of the mechanisms for scanning the structure of the stimulus, carried out by neural networks that produce high-frequency EEG activity (see Reader 2.1; Reader 2.5).

Magnetoencephalography - registration of magnetic field parameters determined by the bioelectrical activity of the brain. These parameters are recorded using superconducting quantum interference sensors and a special camera that isolates the magnetic fields of the brain from stronger external fields. The method has a number of advantages over the registration of a traditional electroencephalogram. In particular, the radial components of magnetic fields recorded from the scalp do not undergo such strong distortions as the EEG. This makes it possible to more accurately calculate the position of the generators of EEG activity recorded from the scalp.