What does eeg mean? EEG during examination of the brain - what does it show? Indications for electroencephalography

Electroencephalography of the brain is a method in electrophysiology that records the bioelectrical activity of brain neurons by removing them from the surface of the head.

The brain has bioelectrical activity. Each nerve cell in the central nervous system capable of creating an electrical impulse and transmitting it to neighboring cells using axons and dendrites. There are approximately 14 billion neurons in the cerebral cortex, each of which creates its own electrical impulse. Individually, each impulse does not represent anything, but every second the total electrical activity of 14 billion cells creates an electromagnetic field around the brain, which is recorded by a brain electrocyfogram.

EEG monitoring reveals functional and organic pathologies of the brain, such as epilepsy or sleep disorders. Electroencephalography is carried out using a device - an electroencephalograph. Is it harmful to perform the procedure with an electroencephalograph: the study is harmless, since the device does not send a single signal to the brain, but only records outgoing biopotentials.

An electroencephalogram of the brain is a graphical representation of the electrical activity of the central nervous system. It depicts waves and rhythms. Their qualitative and quantitative indicators are analyzed and a diagnosis is issued. The analysis is based on rhythms—electrical oscillations of the brain.

Computer electroencephalography (CEEG) is a digital way of recording brain wave activity. Outdated electroencephalographs display the graphical result on a long tape. QEEG displays the result on the computer screen.

The following brain rhythms are identified, recorded on the electroencephalogram:

Alpha rhythm.

Its amplitude increases in a state of quiet wakefulness, for example, when resting or in a dark room. Alpha activity on the EEG decreases when the subject moves on to active work that requires high concentration of attention. People who have been blind all their lives have an absence of alpha rhythm on the EEG.

Beta rhythm.

It is characteristic of active wakefulness with high concentration of attention. Beta activity on the EEG is most clearly expressed in the projection of the frontal cortex. Also on the electroencephalogram, the beta rhythm appears with the sudden appearance of an emotionally significant new stimulus, for example, the appearance of a loved one after several months of separation. Beta rhythm activity also increases during emotional stress and work that requires high concentration.

Gamma rhythm.

This is a collection of low-amplitude waves. The gamma rhythm is a continuation of beta waves. Thus, gamma activity is recorded under high psycho-emotional stress. The founder of the Soviet school of neuroscience, Sokolov, believes that the gamma rhythm is a reflection of the activity of human consciousness.

Delta rhythm.

These are high amplitude waves. It is recorded in the phase of deep natural and medicated sleep. Delta waves are also recorded in a coma state.

Theta rhythm.

These waves are generated in the hippocampus. Theta waves appear on the EEG in two states: the rapid eye movement phase and during high concentration. Harvard professor Schacter argues that theta waves appear during altered states of consciousness, such as deep meditation or trance.

Kappa rhythm.

It is registered in the projection of the temporal cortex of the brain. It appears in the case of suppression of alpha waves and in a state of high mental activity the subject being studied. However, some researchers associate the kappa rhythm with normal eye movement and regard it as an artifact or side effect.

Mu rhythm.

Appears in a state of physical, mental and emotional peace. It is registered in the projection of the motor lobes of the frontal cortex. Mu waves disappear during visualization or during physical activity.

Normal EEG in adults:

Alpha rhythm: frequency – 8-13 Hz, amplitude – 5-100 µV.
Beta rhythm: frequency – 14-40 Hz, amplitude – up to 20 µV.
Gamma rhythm: frequency – 30 or more, amplitude – no more than 15 µV.
Delta rhythm: frequency – 1-4 Hz, amplitude – 100-200 µV.
Theta rhythm: frequency – 4-8 Hz, amplitude – 20-100 µV.
Kappa rhythm: frequency – 8-13 Hz, amplitude – 5-40 µV.
Mu rhythm: frequency – 8-13 Hz, amplitude – on average 50 µV.

Conclusion The EEG of a healthy person consists of precisely these indicators.

Types of EEG

The following types of electroencephalography exist:

Night EEG of the brain with video support. During the study, electromagnetic waves brain, and video and audio studies allow one to assess the behavioral and motor activity of the subject during sleep. Daily EEG monitoring of the brain is used when it is necessary to confirm the diagnosis of epilepsy of complex origin or establish the causes of convulsive seizures.
Brain mapping. This type allows you to map the cerebral cortex and mark pathological emerging foci on it.
Electroencephalography with biofeedback. It is used to train control of brain activity. Thus, when a subject is given sound or light stimuli, he sees his encephalogram and tries to mentally change its indicators. There is little information about this method and it is difficult to assess its effectiveness. It is said to be used for patients who are resistant to antiepileptic drugs.

Indications for use

Electrophysiological research methods, including an electroencephalogram, are indicated in the following cases:

A convulsive seizure was detected for the first time. Seizures. Suspicion of epilepsy. In this case, the EEG reveals the cause of the disease.
Assessing the effectiveness of drug therapy in well-controlled and drug-resistant epilepsy.
Suffered traumatic brain injuries.
Suspicion of a neoplasm in the cranial cavity.
Sleep disorders.
Pathological functional states, neurotic disorders, for example, depression or neurasthenia.
Assessment of brain performance after stroke.
Assessment of involutional changes in elderly patients.

Contraindications

EEG of the brain is an absolutely safe non-invasive method. He registers electrical changes in the brain by removing potentials with electrodes that do not have a negative effect on the body. Therefore, an electroencephalogram has no contraindications and can be performed on any patient who has a brain.

How to prepare for the procedure

How to prepare:

For 3 days, the patient must abandon anticonvulsant therapy and other drugs that affect the functioning of the central nervous system (tranquilizers, anxiolytics, antidepressants, psychostimulants, sleeping pills). These drugs affect the inhibition or excitation of the cerebral cortex, which is why the EEG will not show reliable results.
In 2 days you need to create a small diet. Avoid drinks containing caffeine or other nervous system stimulants. It is not recommended to drink coffee, strong tea, Coca-Cola. You should also limit dark chocolate.
Preparation for the study includes washing your hair: recording sensors are placed on scalp, so clean hair will ensure better contact.
Before the study, it is not recommended to apply hairspray, gel or other cosmetical tools, changing the density and consistency of hair.
Two hours before the test, you should not smoke: nicotine stimulates the central nervous system and can distort the results.

Preparation for an EEG of the brain will show a good and reliable result that does not require repeated testing.

Description of the process using the example of EEG video monitoring. The study can be carried out during the day or at night. The first one usually starts from 9:00 to 14:00. The night option usually starts at 21:00 and ends at 9:00. Lasts all night.

Before starting the diagnosis, the patient is put on an electrode cap, and a gel is applied under the sensors to improve conductivity. The headdress is fixed on the head with clasps and fasteners. The cap is placed on the person's head during the entire procedure. The EEG cap for children under 3 years of age is additionally strengthened due to the small size of the head.

All research is carried out in an equipped laboratory, where there is a restroom, refrigerator, kettle and water. You will talk with a doctor who needs to find out your current state of health and readiness for the procedure. First, part of the study is carried out during active wakefulness: the patient reads a book, watches TV, listens to music. The second period begins during sleep: the bioelectrical activity of the brain is assessed during slow and fast phase sleep, behavioral acts during dreams, the number of awakenings and extraneous sounds, such as snoring or talking during sleep, are assessed. The third part begins after waking up and records brain activity after sleep.

Photostimulation with EEG may be used during this process. This procedure is necessary to assess the difference between brain activity during deprivation of external stimuli and during the presentation of light stimuli. What is noted on the electroencephalogram during photostimulation:

decrease in rhythm amplitude;
photomyoclonus - polyspikes appear on the EEG, which are accompanied by twitching of the facial muscles or muscles of the limbs;

Photostimulation can provoke epileptiform responses or an epileptic seizure. Using this method, hidden epilepsy can be diagnosed.

To diagnose hidden epilepsy, a hyperventilation test with EEG is also used. The subject is asked to breathe deeply and regularly for 4 minutes. This method of provocation allows one to detect on the electroencephalogram epileptiform activity or even provoke a generalized convulsive seizure of an epileptic nature.

Daytime electroencephalography is done in a similar way. It is carried out in a state of active or passive wakefulness. The time required is one to two hours.

How to do an EEG without finding anything? Electrical activity of the brain reveals subtle changes in brain wave activity. Therefore, if there is a pathology, for example, epilepsy or circulatory disorders, a specialist will identify it. Normal and pathological EEGs are always visible, despite all attempts to hide unpleasant results.

When it is impossible to transport the patient, an EEG of the brain is performed at home.

For children

Children undergo EEG using a similar algorithm. The child is put on a mesh cap with fixed electrodes and placed on his head, having first treated the surface of the head with conductive gel.

How to prepare: the procedure does not cause any discomfort or pain. However, children are still scared due to the fact that they are in a doctor’s office or in a laboratory, which already initially forms the idea that it will be unpleasant. Thus, before the procedure, the child should be explained what exactly will happen to him and that the examination is not painful.

A hyperactive child may be prescribed a sedative or sleeping pill before the test. This is necessary so that during the study unnecessary movements of the head or neck do not remove the contact between the sensors and the head. For an infant the study is carried out in a dream.

Result and transcript

An EEG of the brain provides a graphical result of the bioelectrical activity of the central nervous system. This could be a recording on tape or an image on a computer. Decoding an electroencephalogram is an analysis of wave and rhythm indicators. Thus, the obtained indicators are compared with normal frequency and amplitude.

The following types of EEG disorders exist:

Normal indicators, or organized type. Characterized by a main component (alpha waves) that have regular and regular frequencies. The waves are smooth. Beta rhythms are predominantly of medium or high frequency with small amplitude. There are few or almost no slow waves.

The first type is divided into two subtypes:
- a variant of the ideal norm; here the waves are not changed in principle;
- subtle disorders that do not affect the functioning of the brain and mental state person.
Hypersynchronous type. Characterized by a high wave index and increased synchronization. However, the waves retain their structure.
Disturbance of synchronization (flat type of EEG, or desynchronous type of EEG). The severity of alpha activity decreases with an increase in beta wave activity. All other rhythms are within normal limits.
Disorganized EEG with pronounced alpha waves. It is characterized by high activity of the alpha rhythm, but this activity is irregular. A disorganized type of EEG with an alpha rhythm does not have sufficient activity and can be recorded in all areas of the brain. High activity of beta, theta and delta waves is also recorded.
Disorganization of the EEG with a predominance of delta and theta rhythms. Characterized by low alpha wave activity and high slow rhythm activity.

First type: electroencephalogram shows normal brain activity. The second type reflects weak activation of the cerebral cortex, more often indicating a disruption of the brain stem with a violation of the activating function of the reticular formation. The third type reflects increased activation of the cerebral cortex. The fourth type of EEG shows dysfunction in the functioning of the regulatory systems of the central nervous system. The fifth type reflects organic changes in the brain.

The first three types in adults occur either normally or with functional changes, e.g. neurotic disorders or schizophrenia. The last two types indicate gradual organic changes or the onset of brain degeneration.

Changes in the electroencephalogram are often nonspecific, but some pathognomonic nuances make it possible to suspect a specific disease. For example, irritative changes in the EEG are typical nonspecific indicators that can manifest themselves in epilepsy or vascular diseases. With a tumor, for example, the activity of alpha and beta waves decreases, although this is considered irritative changes. Irritative changes have the following indicators: alpha waves intensify, beta wave activity increases.

Focal changes can be recorded on the electroencephalogram. Such indicators indicate focal dysfunction of nerve cells. However, the nonspecificity of these changes does not allow us to draw a limiting line between cerebral infarction or suppuration, since in any case the EEG will show the same result. However, it is known for sure: moderate diffuse changes indicate an organic pathology, not a functional one.

EEG is of greatest value for diagnosing epilepsy. Between individual attacks, epileptiform phenomena are recorded on the tape. In addition to obvious epilepsy, such phenomena are recorded in people who have not yet been diagnosed with epilepsy. Epileptiform patterns consist of spikes, sharp rhythms, and slow waves.

However, some individual characteristics of the brain can produce spikes even when the person does not have epilepsy. This happens in 2%. However, in people suffering from falling illness, epileptiform spikes are recorded in 90% of all diagnostic cases.

Also, using electroencephalography, it is possible to determine the spread of convulsive brain activity. Thus, EEG allows us to establish: pathological activity extends to the entire cerebral cortex or only to some of its areas. This is important for the differential diagnosis of forms of epilepsy and the choice of treatment tactics.

Generalized seizures (convulsions throughout the body) are associated with bilateral abnormal activity and polyspikes. So, the following relationship has been established:

Partial epileptic seizures correlate with spikes in the anterior temporal gyrus.
Sensory impairment during or before epilepsy is associated with abnormal activity near the Rolandic fissure.
Visual hallucinations or decreased visual accuracy during or before a seizure are associated with spikes in the projection of the occipital cortex.

Some syndromes on EEG:

Hypsarrhythmia. The syndrome is manifested by a disturbance in the rhythm of waves, the appearance of sharp waves and polyspikes. Appears when infantile spasms and West syndrome. Most often it confirms a diffuse disorder of the regulatory functions of the brain.
The appearance of polyspikes with a frequency of 3 Hz indicates a minor epileptic seizure, for example, such waves appear in a state of absence. This pathology is characterized by a sudden loss of consciousness for several seconds while muscle tone is preserved and there is no reaction to any external stimuli.
A group of polyspike waves indicates a classic generalized epileptic seizure with tonic and clonic seizures.
Low-frequency spike waves (1-5 Hz) in children under 6 years of age reflect diffuse changes in the brain. In the future, such children are susceptible to psychomotor development disorders.
Commissures in the projection of the temporal gyri. They may be related to benign epilepsy in children.
Dominant slow wave activity, in particular delta rhythms, indicates organic damage brain as a cause of seizures.

Electroencephalography data can be used to judge the state of consciousness in patients. Yes, there is a wide variety specific signs on the tape, which can be used to suggest quality or quantitative violation consciousness. However, here too nonspecific changes often appear, as, for example, with encephalopathy of toxic origin. In most cases, pathological activity on the electroencephalogram reflects organic nature disorders rather than functional or psychogenic.

What signs are used to determine impairment of consciousness on the EEG against the background metabolic disorders:

In a state of coma or stupor, high beta wave activity indicates drug intoxication.
Triphasic broad waves in the projection of the frontal lobes indicate hepatic encephalopathy.
A decrease in the activity of all waves indicates a decrease in the functionality of the thyroid gland and hypothyroidism in general.
In a state of coma in the background diabetes mellitus The EEG shows wave activity in an adult that resembles epileptiform phenomena.
In a state of lack of oxygen and nutrients(ischemia and hypoxia) EEG produces slow waves.

The following parameters on the EEG indicate a deep coma or possible death:

Alpha coma. Alpha waves are characterized by paradoxical activity, this is especially clearly recorded in the projection of the frontal lobes of the brain.
About a strong decline or complete absence brain activity is indicated by spontaneous neural bursts that alternate with occasional high-voltage waves.
“Electrical silence of the brain” is characterized by generalized polyspikes and island-wave rhythms.

Brain disease due to infection manifests itself in nonspecific slow waves:

Virus herpes simplex or encephalitis is characterized by slow rhythms in the projection of the temporal and frontal cortex of the brain.
Generalized encephalitis is characterized by alternating slow and acute waves.
Creutzfeldt-Jakob disease manifests itself on the EEG as three- and two-phase sharp waves.

EEG is used in diagnosing brain death. Thus, with the death of the cerebral cortex, the activity of electrical potentials decreases as much as possible. However, a complete stop of electrical activity is not always permanent. Thus, the dulling of biopotentials can be temporary and reversible, as, for example, with a drug overdose, respiratory arrest

In the vegetative state of the central nervous system, the EEG shows isoelectric activity, which indicates the complete death of the cerebral cortex.

For children

How often can it be done: the number of procedures is not limited, since the study is harmless.

EEG in children has its own peculiarities. An electroencephalogram shows in children under one year old (full-term and painless child) periodic low-amplitude and generalized slow waves, predominantly delta rhythm. This activity has no symmetry. In the projection of the frontal lobes and parietal cortex, the amplitude of the waves increases. Slow wave activity on the EEG in a child of this age is the norm, since the regulatory systems of the brain have not yet been formed.

EEG norms in children aged from one to three months: the amplitude of electrical waves increases to 50-55 μV. There is a gradual establishment of the rhythm of the waves. EEG results in three-month-old children: a mu rhythm with an amplitude of 30-50 μV is recorded in the frontal lobes. The asymmetry of waves in the left and right hemispheres is also recorded. By 4 months of life, the rhythmic activity of electrical impulses is recorded in the projection of the frontal and occipital cortex.

Interpretation of EEG in children one year of age. The electroencephalogram shows oscillations of the alpha rhythm, which alternate with slow delta waves. Alpha waves are characterized by instability and lack of a clear rhythm. In 40% of the entire electroencephalogram, the theta rhythm and delta rhythm (50%) dominate.

Decoding indicators for two-year-old children. Alpha wave activity is recorded in all projections of the cerebral cortex as a sign of gradual activation of the central nervous system. Beta rhythm activity is also noted.

EEG in children 3-4 years old. The theta rhythm dominates in the electroencephalogram; slow delta waves predominate in the projection of the occipital cortex. Alpha rhythms are also present, but they are hardly noticeable against the background of slow waves. With hyperventilation (active forced breathing), sharpening of the waves is noted.

At the age of 5-6 years, the waves stabilize and become rhythmic. Alpha waves already resemble alpha activity in adults. Slow waves no longer overlap alpha waves in their regularity.

EEG in children 7-9 years old records the activity of alpha rhythms, but to a greater extent these waves are recorded in the projection of the crown. Slow waves recede into the background: their activity is no more than 35%. Alpha waves make up approximately 40% of the total EEG, and theta waves make up no more than 25%. Beta activity is recorded in the frontal and temporal cortex.

Electroencephalogram in children 10-12 years old. Their alpha waves are almost mature: they are organized and rhythmic, dominating throughout the entire graphic tape. Alpha activity makes up approximately 60% of all EEG. These waves show the greatest voltage in the region of the frontal, temporal and parietal lobes.

EEG in 13-16 year old children. The formation of alpha waves has completed. The bioelectrical activity of the brain in healthy children acquired the characteristics of the brain activity of a healthy adult. Alpha activity dominates in all parts of the brain.

Indications for the procedure in children are the same as in adults. For children, EEG is prescribed primarily to diagnose epilepsy and determine the nature of seizures (epileptic or non-epileptic).

Convulsions of non-epileptic nature are manifested by the following indicators on the EEG:

Flashes of delta and theta waves are synchronous in the left and right hemispheres, they are generalized and are most expressed in the parietal and frontal lobe.
Theta waves are synchronous on both sides and are characterized by low amplitude.
Arch-shaped spikes are recorded on the EEG.

Epileptic activity in children:

All waves become sharpened, they are synchronous on both sides and generalized. Often occur suddenly. May occur in response to opening the eyes.
Slow waves are filmed in the projection of the frontal and occipital lobe. They are registered during wakefulness and disappear if the child closes his eyes.

One of the main methods used in diagnosing diseases of brain origin is ECG method brain, called in this case EEG - electroencephalography. This study is based on recording electrical signals from the resulting discharges of brain cells, otherwise called biopotentials. Given diagnostic test appeared relatively recently, like most modern methods, actively used at present. The 20th century gave the world EEG, first establishing its use in dogs and then in humans.

The EEG technique helps the doctor assess the performance of the brain, its functionality; often the EEG is more effective in diagnostic terms than the smallest changes in brain tissue in the absence of such changes on a computer tomograph. In addition to its diagnostic value, EEG helps in differentiating diagnoses. For example, with the help of this research method it is possible to distinguish from other pathologies that mimic it, such as panic attack, vegetative paroxysm, neuroses of various origins, psychiatric pathologies.

Video

For comfort long word“electroencephalography” is replaced by both doctors and patients with an abbreviation and called this diagnostic method simply - EEG. It should be noted here that some (probably to enhance the significance of the study) talk about EEG of the brain, but this is not entirely correct, since the Latinized version of the ancient Greek word “encephalon” is translated into Russian as “brain” and in itself is already part of the medical term is encephalography.

Electroencephalography or EEG is a method of studying the brain (BM) in order to identify foci of increased convulsive readiness of its cortex, which is typical for (the main task), tumors, conditions after a stroke, structural and metabolic, sleep disorders and other diseases. Encephalography is based on recording the electrical activity of the brain (frequency, amplitude), and this is done with the help of electrodes attached in different places on the surface of the head.

What kind of research is an EEG?

Periodically occurring convulsive seizures, occurring in most cases with total loss consciousness, is popularly called epilepsy, which official medicine calls epilepsy.

The very first and main method for diagnosing this disease, which has served humanity for many decades (the first EEG recorded dates back to 1928), is encephalography (electroencephalography). Of course, the research apparatus (encephalograph) has now significantly changed and improved, its capabilities with the use of computer technology have expanded significantly. However, the essence of the diagnostic method remains the same.

Electrodes (sensors) are connected to the electroencephalograph, which are placed in the form of a cap on the surface of the subject’s head. These sensors are designed to capture the slightest electromagnetic bursts and transmit information about them to the main equipment (device, computer) for automatic processing and analysis. The encephalograph processes the received impulses, amplifies them and records them on paper in the form of a broken line, very reminiscent of an ECG.

Bioelectric activity of the brain is created mainly in the cortex with the participation of:

The thalamus, which oversees and redistributes information;
ARS (activating reticular system), the nuclei of which are distributed in various parts of the GM (oblongata and midbrain, pons, diencephalic system) receive signals from many pathways and transmit them to all parts of the cortex.

The electrodes read these signals and deliver them to the device, where recording occurs (graphic image - encephalogram). Information processing and analysis - tasks software a computer that “knows” norms of biological activity of the brain and the formation of biorhythms, depending on age and a specific situation.

For example, routine EEG detects the formation of pathological rhythms during an attack or in the period between attacks; sleep EEG or nighttime EEG monitoring shows how the biopotentials of the brain change while immersed in the world of dreams.

Thus, electroencephalography shows the bioelectrical activity of the brain and the consistency of the activity of brain structures during wakefulness or during sleep and answers the questions:

Are there any foci of increased convulsive readiness of the brain, and if they are, in what area are they located?
What stage is the disease at, how far has it progressed or, conversely, has it begun to regress;
What effect does the chosen medicine have and is its dose calculated correctly;

Of course, even the most “smart” machine will not replace a specialist (usually a neurologist or neurophysiologist), who receives the right to decipher an encephalogram after undergoing special training.

Features of EEG in children

What can we say about kids, if some adults, having received a referral for an EEG, begin to ask what and how, because they doubt the safety of this procedure. Meanwhile, it actually cannot cause any harm to the child, but it can be really difficult to perform an EEG on a small patient. For babies under one year old, the bioelectrical activity of the brain is measured during sleep, before this they wash their hair, feed the baby and, without deviating from the usual schedule (sleep/wake), adjust the procedure to the child’s sleep.

But if for children under one year old it is enough to wait until they fall asleep, then a child from one to three years old (and some even older) still needs to be persuaded, therefore, up to 3 years of age, the study is carried out in a state of wakefulness only for calm and sociable children, giving preference in other cases to EEG sleep.

Preparations for visiting the appropriate office should begin several days in advance, turning the future trip into a game. You can try to interest the baby in a pleasant trip, where he can go with his mother and his favorite toy, come up with some other options (usually parents are more aware of how to convince the child to sit quietly, not move, cry or talk). Unfortunately, such restrictions are very difficult for young children to withstand, because they still cannot understand the seriousness of such an event. Well, in such cases the doctor is looking for an alternative...

Indications for performing daytime encephalography in a child in a state of sleep or nighttime EEG are:

Identification of paroxysmal conditions of various origins - epileptic seizures, convulsive syndrome against the background of high body temperature (febrile convulsions), epileptiform seizures not associated with true epilepsy and differentiated from it;
Monitoring the effectiveness of antiepileptic therapy with an established diagnosis of epilepsy;
Diagnosis of hypoxic and ischemic lesions of the central nervous system (presence and severity);
Determination of the severity of brain lesions for prognostic purposes;
Study of the bioelectrical activity of the brain in young patients to study the stages of its maturation and the functional state of the central nervous system.

In addition, it is often suggested to do an EEG with frequent and delayed acquisition of speech skills and stuttering. This method should not be neglected in other cases that require studying the reserves of the functional capabilities of the brain, because the procedure is both harmless and painless, but can provide maximum information for diagnosing a certain pathology. Electroencephalography is very useful if episodes of disturbances of consciousness occur, but their cause is not clear.

Different recording methods

Registration of bioelectric potentials of the brain is carried out different ways, For example:

At the beginning of a diagnostic search that identifies the causes of paroxysmal conditions, a short-term (≈ 15 min) routine method of recording an encephalogram, which, to identify hidden disorders, involves the use of provocative tests - the patient is asked to breathe deeply (hyperventilation), open and close his eyes, or is given light stimulation (photostimulation);
If a routine EEG does not provide the necessary information, the doctor prescribes deprivation encephalography(sleep deprivation at night, completely or partially). To conduct such a study and obtain reliable results, a person is either not allowed to sleep at all, or is woken up 2-3 hours before the subject’s “biological alarm clock” rings;
Long-term EEG recording recording the bioelectrical activity of the brain cortex during “quiet hours” (EEG sleep) occurs if the doctor suspects that changes in the brain occur precisely while in “sleep mode”;
Experts consider the most informative night EEG, which is recorded in a hospital setting. The study begins while you are awake (before going to bed), continues when you fall asleep, covers the entire period of night sleep and ends after natural awakening. If necessary, registration of bioelectrical activity of the brain is supplemented by the application of supernumerary electrodes and the use of video recording equipment.

Long-term recording of electrical activity over several hours during sleep and recording of nighttime EEG is called EEG monitoring. Naturally, such methods require the use of additional equipment and material resources, as well as the patient’s stay in a hospital setting.

Time and equipment make up the price

In other cases, there is a need to measure the biopotentials of the brain at the time of an attack. Pursuing similar goals, the patient, as for conducting an overnight EEG, is sent to a hospital for hospitalization, where 24-hour EEG monitoring is carried out using audio and video equipment. Continuous EEG monitoring with video recording throughout the day makes it possible to verify the epileptic origin of paroxysmal memory disorders, isolated auras, as well as episodic psychomotor phenomena.

Electroencephalography is one of the most available methods brain research. And for the price too. In Moscow, you can find this study for 1,500 rubles, and for 8,000 rubles (EEG sleep monitoring for 6 hours), and for 12,000 rubles (night EEG).

In other cities of Russia you can get by with a smaller amount, for example, in Bryansk the price starts from 1200 rubles, in Krasnoyarsk - from 1100 rubles, and in Astrakhan it starts from 800 rubles.

Certainly, It’s better to get an EEG done in a specialized neurological clinic, where in doubtful cases there is the possibility of a collegial diagnosis (in such institutions many specialists can encrypt the EEG), as well as obtain a doctor’s consultation immediately after the test or quickly resolve the issue regarding other methods of brain research.

About the main rhythms of electrical activity of the brain

When deciphering the research results, take into account various factors: age of the subject, his general state(presence of tremor, weakness in the limbs, visual impairment, etc.), anticonvulsant therapy at the time of recording the bioelectrical activity of the brain, the approximate time(date) of the last seizure, etc.

The electroencephalogram consists of various complex biorhythms emanating from the electrical activity of the brain at different periods of time, depending on specific situations.

When decoding the EEG, first of all, pay attention to the main rhythms and their characteristics:

Alpha rhythm(frequency - in the range from 9 to 13 Hz, oscillation amplitude - from 5 to 100 μV), which is present in almost all people who have no complaints about their health during inactive wakefulness (relaxation during rest, relaxation, shallow meditation) . As soon as a person opens his eyes and tries to visually imagine any picture, α-waves decrease and may disappear altogether if the functional activity of the brain continues to increase. When deciphering the EEG, the following parameters of the α-rhythm are important: amplitude (μV) over the left and right hemispheres, dominant frequency (Hz), dominance of certain leads (frontal, parietal, occipital, etc.), interhemispheric asymmetry (%). Depression of the α-rhythm is caused by anxiety, fear, and activation of autonomic nervous activity;
Beta rhythm(frequency ranges from 13 to 39 Hz, oscillation amplitude is up to 20 μV) - this is not only our wakefulness mode, the β-rhythm is characteristic of active mental work. In a normal state, the expression of β-waves is very weak, their excess indicates an immediate reaction of the brain to stress;
Theta rhythm(frequency – from 4 to 8 Hz, amplitude ranges from 20-100 µV). These waves do not reflect pathological change consciousness, for example, a person is dozing, half asleep, in the stage of superficial sleep, he is already seeing some dreams, and then θ-rhythms are detected. In a healthy person, falling into sleep is accompanied by the appearance of a significant number of θ rhythms. An increase in the theta rhythm is observed during prolonged psycho-emotional stress, mental disorders, twilight states characteristic of some neurological diseases, asthenic syndrome, concussion;
Delta rhythm(frequency ranges from 0.3 to 4 Hz, amplitude from 20 to 200 μV) – typical for deep dive into sleep (natural falling asleep and artificially created sleep - anesthesia). With various neurological pathologies, an increase in the δ wave is observed;

In addition, other electrical oscillations occur in the cerebral cortex: gamma rhythms reaching high frequencies (up to 100 Hz), kappa rhythms formed in the temporal leads during active mental activity, mu rhythms associated with mental stress. These waves are not particularly interesting from a diagnostic point of view, since they arise under significant mental stress and intense “work of thought”, requiring high concentration of attention. An electroencephalogram, as is known, is recorded, although during wakefulness, but in a calm state, and in some cases, overnight EEG or sleep EEG monitoring is even prescribed.

Video: alpha and beta rhythms on EEG

EEG interpretation

main EEG leads and their designations

A bad or good EEG can only be judged after the final interpretation of the study results. Thus, We will talk about a good EEG if, during the waking period, the following were recorded on the encephalogram tape:

In the occipital-parietal leads - sinusoidal α-waves with an oscillation frequency ranging from 8 to 12 Hz and an amplitude of 50 μV;
In the frontal areas - β-rhythms with an oscillation frequency greater than 12 Hz and an amplitude not exceeding 20 μV. In some cases, β-waves alternate with θ-rhythms with a frequency of 4 to 7 Hz and this is also considered normal.

It should be noted that individual waves are not specific to any particular pathology. An example is epileptiform sharp waves, which under some circumstances can appear in healthy people who do not suffer from epilepsy. Conversely, peak-wave complexes (frequency 3 Hz) clearly indicate epilepsy with petit mal seizures, and sharp waves (frequency 1 Hz) indicate a progressive degenerative disease of the brain - Creutzfeldt-Jakob disease, therefore these waves with decoding is considered an important diagnostic feature.

In the period between attacks, epilepsy may not be noticed, since the peaks and sharp waves characteristic of this disease are not observed in all patients who show all clinical symptoms pathology at the time of a convulsive attack. Moreover, paroxysmal manifestations in other cases can be recorded in absolutely healthy people who do not have any signs or prerequisites for the development of a convulsive syndrome.

In connection with the above, having conducted a single study and not finding epileptic activity on the background EEG (“good EEG”), it is impossible to completely exclude epilepsy based on the results of one test if clinical signs of the disease occur. It is necessary to further examine the patient for this unpleasant disease using other methods.

Recording an EEG during a seizure in a patient with epilepsy may provide the following options:

Frequent electrical discharges of high amplitude, which indicate that the peak of the attack has occurred, slowing down of activity - the attack has entered the attenuation phase;
Focal epiactivity (it indicates the location of the focus of convulsive readiness and the presence partial seizures– we will have to look for the cause of focal lesions of the brain);
Manifestations of diffuse changes (registration of paroxysmal discharges and peak-wave) - such indicators indicate that the attack is generalized.

As for other diseases in which pathological electrical activity has nothing to do with epilepsy, they can be recorded in the form of focal brain lesions and diffuse changes. For example, a slow rhythm with a predominance of θ- and δ-waves is considered a generally valid identifier of twilight consciousness of various origins (, ), which, in the case of focal brain damage, manifests itself more noticeably on the side of the suffering of the brain than on the healthy side.

If the origin of the brain lesion is established, and diffuse changes are recorded on the EEG, then diagnostic value this study although not so significant, it still makes it possible to find one or another disease that is far from epilepsy:

Meningitis (especially caused by herpetic infection) - on the EEG: periodic formation of epileptiform discharges;
Metabolic encephalopathy - on the encephalogram: the presence of “triphasic” waves or diffuse slowdowns in rhythm and bursts of symmetrical slow activity in the frontal areas.

Diffuse changes in the encephalogram can be recorded in patients who have suffered a brain injury or concussion, which is understandable - with severe head injuries, the entire brain suffers. However, there is another option: diffuse changes are found in people who do not have any complaints and consider themselves absolutely healthy. It happens and if not clinical manifestations pathology, then there is no reason to worry either. Perhaps, at the next examination, the EEG recording will reflect complete normality.

In what cases does EEG help make a diagnosis?

Electroencephalography, revealing the functionality and reserves of the central nervous system, has become the standard for brain research; doctors consider it advisable to carry it out in many cases and for various states:

To assess the degree of functional immaturity of the brain in young patients (in a child under one year old, the study is always carried out during sleep, in older children - depending on the situation);
At various violations sleep (frequent awakenings at night, etc.);
In the presence of epileptic seizures;
To confirm or exclude complications of inflammatory processes caused by neuroinfection;
At ;
After
In some cases, the study requires surgical operations (determining the depth of anesthesia);
Encephalography will help to recognize how far neuropsychic disorders have gone in hepatic cellular failure (hepatic encephalopathy), as well as in other forms of metabolic encephalopathies (renal, hypoxic);
All drivers (future and current), when undergoing a medical examination to obtain/replace a license, are asked to undergo an EEG for a certificate provided by the traffic police. The examination is easy to use and easily identifies those who are completely unfit to drive vehicles, which is why it was adopted;
Electroencephalography is prescribed to conscripts with a history of convulsive syndrome (based on data medical card) or in case of complaints of attacks with loss of consciousness accompanied by convulsions;
In some cases, a study such as EEG is used to ascertain the death of a significant part of nerve cells, that is, brain death(we are talking about situations when they say that “a person most likely turned into a plant”).

Video: EEG and detection of epilepsy

The study does not require special preparation

An EEG does not require any special preparation, but some patients are openly afraid of the upcoming procedure. It’s no joke - sensors with wires are placed on the head, which read “everything that is happening inside the skull” and transmit the full amount of information to the “smart” device (in fact, the electrodes record changes in the potential difference between two sensors in different leads). Adults are provided with symmetrical attachment to the surface of the head of 20 sensors + 1 unpaired one, which is superimposed on the parietal region, small child 12 is enough.

Meanwhile, I would like to reassure particularly suspicious patients: the study is absolutely harmless, has no restrictions on frequency and age (at least several times a day and at any age - from the first days of life to old age, if circumstances so require).

The main preparation is to ensure the cleanliness of the hair, for which the day before the patient washes his hair with shampoo, rinses and dries well, but does not use any chemical hair styling products (gel, foam, varnish). Metal objects used for decoration (clips, earrings, hairpins, piercings) are also removed before an EEG is performed. Besides:

For 2 days, they give up alcohol (strong and weak), do not drink drinks that stimulate the nervous system, and do not indulge in chocolate;
Before the study, obtain doctor's advice regarding medications taken. medicines(hypnotics, tranquilizers, anticonvulsants, etc.). It is possible that certain medications will have to be discontinued in consultation with the treating doctor, and if this cannot be done, then you should inform the doctor who will be involved in deciphering the encephalogram (a note on the referral form) so that he keeps these circumstances in mind and takes them into account when drawing up the conclusion.
2 hours before the examination, patients should not allow themselves a heavy meal and relaxation with a cigarette (such activities can distort the results);
It is not recommended to do an EEG in the midst of an acute respiratory disease, as well as coughing and nasal congestion, even if these signs do not relate to an acute process.

When all the rules of the preparatory stage are followed, individual points are taken into account, the patient is seated in a comfortable chair, the places where the surface of the head comes into contact with the electrodes are lubricated with gel, sensors are attached, a cap is put on or dispensed with, the device is turned on - the recording begins... Provocative tests are used as needed during time of registration of bioelectrical activity of the brain. As a rule, this need arises when routine methods do not provide adequate information, that is, when epilepsy is suspected. Techniques that provoke epileptic activity ( deep breathing, opening and closing the eyes, sleep, light irritation, sleep deprivation), activate the electrical activity of the GM cortex, the electrodes capture the impulses sent by the cortex and transmit them to the main equipment for processing and recording.

In addition, if epilepsy is suspected (especially temporal epilepsy, which in most cases presents difficulties in diagnosis), special sensors are used: temporal, sphenoidal, nasopharyngeal. And, it should be noted, doctors have officially admitted that in many cases it is the nasopharyngeal abduction that detects the focus of epileptic activity in the temporal region, while other leads do not react to it in any way and send normal impulses.

Video: specialists about EEG - information for patients

Video: conducting an EEG - medical film

EEG, or electroencephalography, is a diagnostic method for studying the functional activity of brain neurons. It is based on the registration of impulses emanating from certain brain centers, followed by their decoding. It is used to identify pathological processes occurring in the central nervous system (for example, if epilepsy, cancer, and others are suspected). What does the EEG of the brain show? Why is this examination prescribed? More on this later in the article.

What is the essence of the procedure?

EEG can be performed on patients of all ages

Nerve cells located in the head, while performing their functions, generate an electrical impulse with a certain frequency and amplitude. This neuronal activity can be detected and recorded by placing electrodes on the surface of the head. As a result, everything that the EEG reveals will be reflected on paper or a monitor in the form of waves.

U different people their indicators of electrical activity of nerve cells in the brain.

Despite the fact that average indicators do exist, when deciphering an electroencephalogram, specialists must take into account such parameters as: age characteristics, the presence or absence of neurological diseases, the therapy being carried out at the time of the study (or its absence) and others.

What brain rhythms are recorded by an electroencephalogram?

As mentioned above, electrical oscillations arising in the neurons of the cerebral cortex are displayed on the monitor screen in the form of waves. Changes in the following rhythms are of diagnostic importance: alpha, beta, theta, delta. There are other rhythms of functional activity of neurons (gamma, kappa, mu). However, they are not of particular interest in terms of diagnosis, since their occurrence is associated with a fairly high mental and mental load. And what the electroencephalogram of the brain shows is revealed in a state of complete rest, sometimes during sleep.

Types of Brain Waves

Brain rhythms

So, what does an EEG of the brain reveal? Below are the main rhythms of electrical activity of neurons in the cerebral cortex and their brief characteristics.

Alpha rhythm. Characterized by a frequency of 8-13 Hz and an amplitude of approximately 50 μV. Such indicators are normally recorded by the device at a time when a person is awake, but does not show physical and mental activity. In addition, his eyes must be closed. When opening your eyes visual analyzer is included in the work, as a result of which the activity of nerve cells increases; in this case, alpha waves turn into waves with a higher frequency - beta. The same happens with sounds, any activity, feelings of fear, anxiety and other conditions.
Beta rhythm. The frequency range of these waves is between 14-30 Hz and the amplitude is approximately 25 µV. In a calm state they are expressed to a small extent. An increase in the beta rhythm is caused by a stress factor, as well as high mental activity.
Theta rhythm. These waves are characterized by a frequency of 4-7 Hz and an amplitude of about 100 μV. Theta waves occur when a person begins to doze off. In addition, they intensify with various neurological pathologies, concussion, prolonged stress, emotional and mental overload, and mental disorders.
Delta rhythm. Occurs during deep sleep(including under the influence of anesthesia), as well as under various pathological processes in the brain. Characterized by a frequency of 0.5-3.5 Hz and an amplitude of 100-300 μV.

What does an electroencephalogram show?

The device for conducting EEG is called an electroencephalograph

The curve that appears on the monitor screen during an EEG makes it possible to diagnose various changes in the functioning of nerve cells in the brain. A specialist, assessing the activity of neurons reflected in the encephalogram, can determine the following points:

find out the presence or absence of disorders in the cerebral cortex;
assess the severity of brain damage if it is detected;
accurately determine the location of the injury;
identify those areas of the brain that are the source of epileptic seizures;
study the features of the periodization of sleep and wakefulness;
detect a neoplasm;
determine how effective drug therapy was;
find out how the brain works in the periods between attacks;
discover the cause fainting states and other moments of crisis and much more.

Features of deciphering the electroencephalogram

Based on what the EEG shows, the specialist makes a transcript and draws up a conclusion. The following are considered good results:

the alpha rhythm is fixed in the occipital and parietal regions, and its frequency and amplitude are within normal limits;
indicators of the frequency and amplitude of beta waves also have normal values and are recorded in the forehead (they can alternate with theta waves, which are at their normal frequency).

When deciphering, it is important to take into account that the rhythms themselves, taken separately, do not indicate the presence of any specific disease or disorder. For example, at healthy people waves characteristic of epilepsy may be recorded. Besides, EEG readings carried out in the intervals between epileptic seizures, changes are not recorded in all patients. Thus, if the examination did not reveal neural activity corresponding to epilepsy, this does not mean that the disease does not exist (provided that there are pronounced clinical symptoms). In this case, the doctor chooses other diagnostic methods.

Juvenile absence epilepsy

What else does the EEG of the brain show in an adult? Other diseases (except epilepsy) can be detected using electroencephalography in the form of lesions. So, if an increase in delta and theta rhythms is recorded, then the specialist can assume the presence of a tumor, edema, or stroke.

Diffuse changes in the brain can be evidence of diseases and conditions such as:

concussion, head injuries;
meningitis;
encephalopathy.

In some cases, an EEG study can show changes in the functional activity of neurons in people who do not complain about their health.

If this happens, do not panic, especially since there are no clinical symptoms. EEG analysis at the next diagnosis will most likely show normal results.

Carrying out EEG diagnostics in childhood

Before the procedure, a helmet with electrodes is placed on the child’s head.

In some cases, the doctor may prescribe diagnostics using electroencephalography in a child. The most common indications are:

injuries, head concussion;
frequent crying for no apparent reason;
fluctuations in blood pressure;
sleep disorders;
nervous convulsions, attacks;
fainting;
complaints of headache;
irritability, unstable behavior;
dizziness and other symptoms and conditions.

Analysis of what the electroencephalogram shows makes it possible to assess the development of the child in the first year of life, shows whether the formation of the central nervous system in the baby is occurring correctly, and allows us to identify ischemic areas on early stage. If any pathologies are detected, the doctor has the opportunity to stop them further development and eliminate the disease through timely therapy.

EEGs are usually performed in children while they are asleep. The procedure is absolutely safe for the child’s health, so parents should not worry, even if it is prescribed for a newborn.

Despite the fact that the electroencephalogram is considered an outdated diagnostic method, which is being actively replaced by more modern CT and MRI, it is still relevant. This is explained by its sufficient information content, low cost and accessibility. Therefore, if your doctor has directed you to undergo an EEG procedure, you should not neglect it.

An encephalogram is a non-invasive medical diagnostic method that involves recording the electrical activity of the brain. In the central nervous system, each cell has the property of excitation. This process is accompanied by the formation of an electrical potential. The sum of all the energy from each cell forms an electric field around the brain, which is recorded by the encephalogram of the head. In brain diseases, the activity of the central nervous system is disrupted, which provokes a change in the electrical field of the brain. The purpose of the method is to identify these changes.

As an applied method, the method is used in neurology and psychiatry. Here, an encephalogram detects infectious and non-infectious brain diseases, for example, epilepsy. As a theoretical (for research), the method is used in electrophysiology, neuropsychology and psychophysiology.

How long is it valid? EEG has no expiration date. The doctor himself determines whether a repeat scan is needed or not. It depends on the indications and condition of the patient. For example, a psychiatrist may accept results from a month ago and reject an EEG that was done yesterday.

The electrical field of the head is expressed in brain rhythms, which have frequency and amplitude. The human brain has the following rhythms:

Alpha rhythm.

It has a frequency from 8 to 14 Hz, amplitude from 30 to 70 μV. It is recorded in healthy people in a state of rest or quiet wakefulness. It is most pronounced when a person closes his eyes or in a dark room. Disappears when actively switched on.

Beta rhythm.

Frequency: 15 to 30 Hz. Amplitude: from 5 to 30 µV. It is recorded in a state of active wakefulness, when a person’s attention is involved in work or an intense task. Beta waves increase when the subject is presented with new information or a sudden stimulus, such as an unexpected loud noise. Also, the beta rhythm is recorded in one of the stages of sleep - rapid eye movement - the period when a person dreams.

Gamma rhythm.

Frequency: from 30 Hz. Amplitude: no more than 15 µV. Gamma waves are observed during the active work of the subject, with maximum concentration of attention.

Delta rhythm.

Frequency: up to 4 Hz. Amplitude: from 20 to 200 µV. The delta rhythm is recorded during the period of the body's recovery processes, for example, at the stage of deep sleep, when the cerebral cortex has low level activation.

Theta rhythm.

Frequency: 4-8 Hz. Amplitude: from 20 to 100 µV. Theta waves are recorded during the transition from active wakefulness to drowsiness, that is, when the level of activation of the central nervous system decreases. In other words, theta waves appear at the threshold of sleep. The theta rhythm is also activated when the subject's emotional stress increases.

Other rhythms: kappa, tau, lambda, mu. As a rule, they do not have diagnostic value in physiology, and therefore are often simply not considered or recorded. For example, the kappa rhythm is a diagnostic artifact that appears during eye movements.

Encephalogram as a diagnostic method

The encephalogram determines the functioning of the brain in various states: during sleep, wakefulness, mental and physical work. This is a harmless method: it does not affect the body, but only records changes in the electric field. How often can I do it? The purpose of the method does not depend on the duration of the previous study, so it can be carried out even every day.

The study is prescribed if a brain pathology is suspected. An encephalogram should be performed for the following symptoms:

Convulsive seizures.
Frequent fainting.
Suspicion of a tumor.
General cerebral symptoms, including chronic headache, dizziness, nausea and vomiting.
Autonomic disorders: heavy sweating, constipation, trembling limbs.
Cognitive disorders: impaired attention, memory, thinking.
Nonspecific symptoms: irritability, constant weakness, emotional lability.
Circulatory disorders: , hemorrhagic and.

The study is also necessary for routine prevention and for people of specific professions. For example, an encephalogram of the brain is performed for a category D and C driver's license - an area where drivers are responsible for people and massive cargo.

A variation of the method is an overnight encephalogram. The procedure is performed while the patient is sleeping. Today this is considered a reliable option, which has the greatest diagnostic value in the study of epileptic diseases. The overnight procedure also helps in the diagnosis of insomnia spectrum disorders: difficulty falling asleep, deep sleep, awakening, nightmares and horrors.

Contraindications: none. The method is harmless. But some conditions do not allow the study, for example, open wounds the head is the place where you need to apply electrodes to record the electric field. An encephalogram can also be performed during pregnancy.

What do they use?

The study is carried out using an electroencephalograph. This is an electrical measuring device that records changes in the electrical potential of the brain.

The device consists of a switch, an amplifier, a recording apparatus and a calibration system. Other components are electrodes and light-sound stimulators.

One of the main external components is a helmet-mesh, to which overhead bridge electrodes are attached. This helmet is placed on the head of the subject, after which the registration of the electric field is turned on. The information is transferred to the computer. A graphical result is displayed on his monitor - waves reflecting the bioelectrical activity of the brain.

How is it carried out?

How to prepare: There is no specific preparation for the procedure. The main thing is to calm down and tune in to work, because anxiety distorts the results.

How to do an encephalogram of the brain:

The patient removes outer clothing and jewelry.
He lies down on the couch and takes a sedative to calm him down.
A mesh helmet is put on the head. It connects to the computer.
Actually the research itself. From time to time, the doctor asks you to follow a simple command, such as closing your eyes and imagining something.

How do they give an encephalogram to a child if he is excited? The study can be carried out during sleep. The results of the study are not distorted.

Decoding the electroencephalogram

The EEG result is displayed on a graphic tape on which 5-7 waves are plotted in parallel. Decoding the encephalogram is to identify pathological deviations in rhythms.

Alpha waves.

Violation of alpha waves shows an adult the probable asymmetry of the cerebral hemispheres, the development of tumors, circulatory disorders, for example, with hemorrhage in the subarachnoid space, or traumatic brain injury.

An encephalogram can show the absence of alpha waves in the following pathologies: profound mental retardation. An encephalogram of a child in the absence of alpha rhythms indicates a delay in psychomotor development.

Beta rhythm.

A decrease in these waves indicates severe emotional shock and chronic stress. An increase in amplitude and frequency indicates an inflammatory process in the brain. Excessively high amplitude appears with encephalitis. Abnormalities in the frequency of beta waves may indicate a delay in the child’s mental development.

Delta and theta waves.

Violations in the amplitude of these waves indicate possible tumor processes brain High wave delta and theta waves inform about possible delay development of the child’s central nervous system.

The remaining rhythms actually have no diagnostic value.