Under the complex name lies a safe, easy-to-perform method of studying the brain that captures electrical impulses and records their rhythm and frequency. An electroencephalogram of the brain provides information about the functional characteristics of this organ.

EEG is a test that can be performed on patients of all ages and in any condition. An electroencephalograph, a research device, is indispensable in intensive care wards. This is what is connected to patients in a coma to monitor the slightest changes in the electrical activity of the brain.

Electroencephalography can be carried out in parallel with the patient's exposure to irritating factors: sounds, light, sleep deprivation. This gives a clearer picture of the nature of the disorder and areas of epileptic activity.

Indications

After an EEG, it is more likely to exclude or confirm the presence of such pathologies in a person as:

  • vegetative-vascular dystonia;
  • brain inflammation;
  • neoplasms;
  • epilepsy;
  • hypertonic disease;
  • nervous disorders;
  • cervical osteochondrosis;
  • traumatic brain injury.

An electroencephalogram of the brain reflects the state of the organ in the postoperative period, after a stroke, and the dynamics of changes after treatment. It is required when passing a medical examination to obtain a driving category C and D.

How to prepare

You need to prepare for the examination. Tell your doctor if you are taking certain medicines. Some of them affect brain activity and should be discontinued 3-4 days before the examination. These medications include anticonvulsants and tranquilizers.

On the eve of the EEG and on the day of the test, you should not consume caffeine-containing products and energy drinks: coffee, tea, chocolate, energy drinks. You can't drink alcohol. These foods have a stimulating effect on the brain, and the brain's encephalogram will be distorted.

It is advisable to eat a few hours before the examination.

It is recommended to wash your hair, but do not apply hairspray, styling foam, or other cosmetics. The fats and other components they contain can worsen the contact of the electrodes with the scalp. Braids and dreadlocks will have to be unbraided, and earrings and jewelry removed.

During the procedure, you need to remain calm and not be nervous. Nothing bad happens, and the procedure is completely harmless.

Carrying out an EEG

Typically, electroencephalography is carried out in a specially equipped room, protected from noise and bright light, in which there is a stationary electroencephalograph. If it is necessary to conduct an EEG on site, mobile devices are used.

The patient is asked to lie down on a couch or sit comfortably in a chair. A helmet or cap with electrodes is placed on the head, the number of which depends on the age of the patient. To a small child 12 electrodes are enough; for adults, 21 are used. The electrode cavity is filled with a special substance that facilitates the rapid transmission of electrical impulses. Signals coming from the area next to the electrode have the greatest clarity and strength. Signals received from remote areas are weak.

The cap is connected to an encephalograph, which is capable of detecting vibration frequencies of 0.5 - 100 Hz and serves as an amplifier. The electrical signal is amplified by the encephalograph millions of times and transmitted for subsequent processing to a computer. Here, a huge number of signals are converted into a graph - an encephalogram, which is analyzed by the doctor.

The patient must remain calm and not move during the examination. Only at the very beginning may the doctor ask him to blink several times to assess the nature of the technical errors. If the patient urgently needs to change body position or go to the toilet, the study is stopped. In a situation where he made an involuntary movement, moved, the doctor makes an appropriate note so that during further analysis false information does not appear.

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An encephalogram of the brain is recorded for about 15-20 minutes.

EEG with provocative tests

If necessary, after the main recording, provocative tests are done:

  1. With hyperventilation - the patient is asked to breathe deeply for several minutes.
  2. Test with bright light. It uses a special device capable of reproducing repeating light pulses. An electroencephalogram of the brain records the patient's reaction.
  3. Test with an unexpected sound.

Tests help to find out the real cause of the disorder - it is a manifestation of a pathological process, mental disorder or simulation. If there is a real pathology, testing may provoke an epileptic attack or convulsion. Therefore, the doctor conducting the diagnosis has the experience and knowledge necessary to provide urgent care. The time required for the sample procedure increases.

EEG with sleep deprivation

If there is a suspicion that a conventional EEG did not provide complete and reliable information, electroencephalography with sleep deprivation is prescribed. Some sources indicate that only in 20-30% of cases, when performed in a standard manner, an encephalogram of the head shows signs of epilepsy. Data obtained during sleep is considered more accurate. Before the study, an adult should not sleep for 18 hours. In some cases, if the examination is carried out in a hospital, the patient is woken up in the middle of the night and forced to undergo diagnostics.

If the patient was able to fall asleep quickly, the procedure takes about an hour. The doctor or nurse makes notes regarding any changes in the patient: flinching, movements of the eyes, arms, legs. In the future, the encephalogram of the brain will be interpreted with their help.

At the end of the procedure, the patient is woken up, his condition is checked and sent home or to the ward. After the diagnosis, rest is recommended.

Features of EEG in children

It is not easy to conduct an EEG of the brain in a small child. It scares him a large number of wires, a strange cap, unfamiliar surroundings, people, devices. It is quite difficult to convince your baby that he will have to lie still for some time. Young children are examined during sleep. Before the study, they need to limit the rest time so that he is tired and wants to sleep before the study. On the day of the examination, babies are woken up 4-6 hours before the usual wake-up time. Younger children school age- in 6-8 hours, and children over 12 years old are not allowed to fall asleep at night at all.

The concept of “rhythm” in EEG refers to a certain type of electrical activity corresponding to a certain state of the brain and associated with certain cerebral mechanisms. When describing a rhythm, its frequency is indicated, typical for a certain state and region of the brain, amplitude and some characteristic features of its changes over time with changes in the functional activity of the brain.

  1. Alpha(a) rhythm: frequency 8-13 Hz, amplitude up to 100 µV. It is registered in 85-95% of healthy adults. It is best expressed in the occipital regions. The a-rhythm has the greatest amplitude in a state of calm, relaxed wakefulness with eyes closed. In addition to changes associated with the functional state of the brain, in most cases spontaneous changes in the amplitude of the a-rhythm are observed, expressed in an alternating increase and decrease with the formation of characteristic “spindles” lasting 2-8 s. With an increase in the level of functional activity of the brain (intense attention, fear), the amplitude of the a-rhythm decreases. High-frequency, low-amplitude irregular activity appears on the EEG, reflecting desynchronization of neuronal activity. With a short-term, sudden external irritation (especially a flash of light), this desynchronization occurs abruptly, and if the irritation is not of an emotional nature, the a-rhythm is restored quite quickly (after 0.5-2 s). This phenomenon is called “activation reaction”, “orienting reaction”, “a-rhythm extinction reaction”, “desynchronization reaction”.
  2. Beta rhythm: frequency 14-40 Hz, amplitude up to 25 µV. The beta rhythm is best recorded in the area of ​​the central gyri, but also extends to the posterior central and frontal gyri. Normally, it is expressed very weakly and in most cases has an amplitude of 5-15 μV. The beta rhythm is associated with somatic sensory and motor cortical mechanisms and produces an extinction response to motor activation or tactile stimulation. Activity with a frequency of 40-70 Hz and an amplitude of 5-7 μV is sometimes called the y-rhythm, clinical significance he does not have.
  3. Mu rhythm: frequency 8-13 Hz, amplitude up to 50 µV. The parameters of the mu rhythm are similar to those of the normal a rhythm, but the mu rhythm differs from the latter in physiological properties and topography. Visually, the mu rhythm is observed only in 5-15% of subjects in the rolandic region. The amplitude of the mu rhythm (in rare cases) increases with motor activation or somatosensory stimulation. In routine analysis, the mu rhythm has no clinical significance.

Types of activities that are pathological for an adult awake person

  • Theta activity: frequency 4-7 Hz, amplitude of pathological theta activity >40 μV and most often exceeds the amplitude of normal brain rhythms, reaching 300 μV or more in some pathological conditions.
  • Delta activity: frequency 0.5-3 Hz, amplitude same as theta activity.

Theta and delta oscillations may be present in small quantities on the EEG of an adult awake person and are normal, but their amplitude does not exceed that of the a-rhythm. An EEG containing theta and delta oscillations with an amplitude of >40 μV and occupying more than 15% of the total recording time is considered pathological.

Epileptiform activity is a phenomenon typically observed on the EEG of patients with epilepsy. They arise from highly synchronized paroxysmal depolarization shifts in large populations of neurons, accompanied by the generation of action potentials. As a result of this, high-amplitude, acute-shaped potentials arise, which have appropriate names.

  • Spike (English spike - tip, peak) is a negative potential of an acute form, lasting less than 70 ms, with an amplitude >50 μV (sometimes up to hundreds or even thousands of μV).
  • An acute wave differs from a spike in that it is extended in time: its duration is 70-200 ms.
  • Sharp waves and spikes can combine with slow waves to form stereotypical complexes. Spike-slow wave is a complex of a spike and a slow wave. The frequency of the spike-slow wave complexes is 2.5-6 Hz, and the period, respectively, is 160-250 ms. Acute-slow wave - a complex of an acute wave and a slow wave following it, the period of the complex is 500-1300 ms.

An important characteristic of spikes and sharp waves is their sudden appearance and disappearance and a clear difference from background activity, which they exceed in amplitude. Acute phenomena with appropriate parameters that are not clearly distinguished from background activity are not designated as sharp waves or spikes.

Combinations of the described phenomena are designated by some additional terms.

  • Burst is a term used to describe a group of waves with a sudden appearance and disappearance, clearly different from background activity in frequency, shape and/or amplitude.
  • A discharge is a flash of epileptiform activity.
  • An epileptic seizure pattern is a discharge of epileptiform activity typically coinciding with a clinical epileptic seizure. The detection of such phenomena, even if it is not possible to clearly assess the patient's state of consciousness clinically, is also characterized as an “epileptic seizure pattern.”
  • Hypsarrhythmia (Greek “high-amplitude rhythm”) is a continuous generalized high-amplitude (>150 μV) slow hypersynchronous activity with sharp waves, spikes, spike-slow wave complexes, polyspike-slow wave, synchronous and asynchronous. An important diagnostic feature of West and Lennox-Gastaut syndromes.
  • Periodic complexes are high-amplitude bursts of activity, characterized by a constant form for a given patient. The most important criteria for their recognition are: close to constant interval between complexes; continuous presence throughout the entire recording, subject to a constant level of functional brain activity; intra-individual stability of form (stereotyping). Most often they are represented by a group of high-amplitude slow waves, sharp waves, combined with high-amplitude, pointed delta or theta oscillations, sometimes reminiscent of epileptiform acute-slow wave complexes. The intervals between complexes range from 0.5-2 to tens of seconds. Generalized bilateral synchronous periodic complexes are always combined with profound disturbances of consciousness and indicate severe brain damage. If they are not caused by pharmacological or toxic factors (alcohol withdrawal, overdose or sudden withdrawal of psychotropic and hypnosedative drugs, hepatopathy, carbon monoxide poisoning), then, as a rule, they are a consequence of severe metabolic, hypoxic, prion or viral encephalopathy. If intoxication or metabolic disorders are excluded, then periodic complexes with high certainty indicate a diagnosis of panencephalitis or prion disease.

Variants of the normal electroencephalogram of an adult awake person

The EEG is essentially uniform across the entire brain and symmetrical. The functional and morphological heterogeneity of the cortex determines the characteristics of the electrical activity of various areas of the brain. Spatial changes in EEG types of individual brain regions occur gradually.

In the majority (85-90%) of healthy adults, with their eyes closed at rest, the EEG shows a dominant a-rhythm with maximum amplitude in the occipital regions.

In 10-15% of healthy subjects, the amplitude of oscillations on the EEG does not exceed 25 μV; high-frequency low-amplitude activity is recorded in all leads. Such EEGs are called low-amplitude. Low-amplitude EEGs indicate the predominance of desynchronizing influences in the brain and are a normal variant.

In some healthy subjects, instead of the alpha rhythm, activity of 14-18 Hz with an amplitude of about 50 μV is recorded in the occipital regions, and, like the normal alpha rhythm, the amplitude decreases in the anterior direction. This activity is called the “fast a-variant.”

Very rarely (0.2% of cases), regular, close to sinusoidal, slow waves with a frequency of 2.5-6 Hz and an amplitude of 50-80 μV are recorded on the EEG with eyes closed in the occipital regions. This rhythm has all the other topographic and physiological characteristics of the alpha rhythm and is called the “slow alpha variant.” Not being associated with any organic pathology, it is considered as borderline between normal and pathological and may indicate dysfunction of diencephalic nonspecific brain systems.

Electroencephalogram changes in the sleep-wake cycle

  • Active wakefulness (during mental stress, visual tracking, learning and other situations requiring increased mental activity) is characterized by desynchronization of neuronal activity; low-amplitude, high-frequency activity predominates on the EEG.
  • Relaxed wakefulness is the state of the subject resting in a comfortable chair or on a bed with relaxed muscles and closed eyes, not engaged in any special physical or mental activity. Most healthy adults in this condition show a regular alpha rhythm on the EEG.
  • The first stage of sleep is equivalent to dozing. The EEG shows the disappearance of the alpha rhythm and the appearance of single and group low-amplitude delta and theta oscillations and low-amplitude high-frequency activity. External stimuli cause bursts of alpha rhythm. Duration of the stage is 1-7 minutes. Towards the end of this stage, slow oscillations with an amplitude appear
  • The second stage of sleep is characterized by the appearance of sleep spindles and K-complexes. Sleepy spindles are bursts of activity with a frequency of 11-15 Hz, predominant in the central leads. The duration of the spindles is 0.5-3 s, the amplitude is approximately 50 μV. They are connected With median subcortical mechanisms. The K-complex is a burst of activity typically consisting of a biphasic high-amplitude wave with an initial negative phase, sometimes followed by a spindle. Its amplitude is maximum in the area of ​​the crown, duration is not less than 0.5 s. K-complexes occur spontaneously or in response to sensory stimuli. At this stage, bursts of polyphasic high-amplitude slow waves are also occasionally observed. There are no slow eye movements.
  • The third stage of sleep: spindles gradually disappear and delta and theta waves with an amplitude of more than 75 μV appear in an amount from 20 to 50% of the time of the analysis epoch. At this stage it is often difficult to differentiate K-complexes from delta waves. Sleep spindles may disappear completely.
  • The fourth stage of sleep is characterized by waves with a frequency
  • During sleep, a person occasionally experiences periods of desynchronization on the EEG - so-called rapid eye movement sleep. During these periods, polymorphic activity with a predominance of high frequencies is recorded. These periods on the EEG correspond to the experience of a dream, a drop in muscle tone with the appearance of rapid movements of the eyeballs and sometimes rapid movements of the limbs. The occurrence of this stage of sleep is associated with the work of the regulatory mechanism at the level of the pons; its disturbances indicate dysfunction of these parts of the brain, which is of important diagnostic significance.

Age-related changes in the electroencephalogram

The EEG of a premature baby up to 24-27 weeks of gestation is represented by bursts of slow delta and theta activity, occasionally combined with sharp waves, lasting 2-20 s, against a background of low-amplitude (up to 20-25 μV) activity.

In children 28-32 weeks of gestation, delta and theta activity with an amplitude of up to 100-150 μV becomes more regular, although it may also include bursts of higher amplitude theta activity, interspersed with periods of flattening.

In children older than 32 weeks of gestation, functional states begin to be visible on the EEG. In quiet sleep, intermittent high-amplitude (up to 200 μV and above) delta activity is observed, combined with theta oscillations and sharp waves and interspersed with periods of relatively low-amplitude activity.

In a full-term newborn, the EEG clearly shows differences between wakefulness and with open eyes(irregular activity with a frequency of 4-5 Hz and an amplitude of 50 μV), active sleep (constant low-amplitude activity of 4-7 Hz with superimposition of faster low-amplitude oscillations) and restful sleep characterized by bursts of high-amplitude delta activity in combination with spindles of faster high-amplitude waves, interspersed with low-amplitude periods.

In healthy premature infants and full-term newborns, alternating activity during quiet sleep is observed during the first month of life. The EEG of newborns contains physiological acute potentials, characterized by multifocality, sporadic occurrence, and irregular pattern. Their amplitude usually does not exceed 100-110 µV, the frequency of occurrence is on average 5 per hour, the main number of them is confined to restful sleep. Relatively regularly occurring sharp potentials in the frontal leads, not exceeding 150 μV in amplitude, are also considered normal. A normal EEG of a mature newborn is characterized by the presence of a response in the form of EEG flattening to external stimuli.

During the first month of life of a mature child, the alternating EEG of quiet sleep disappears; in the second month, sleep spindles appear, organized dominant activity in the occipital leads, reaching a frequency of 4-7 Hz at the age of 3 months.

During the 4-6th month of life, the number of theta waves on the EEG gradually increases, and delta waves decrease, so that by the end of the 6th month the rhythm with a frequency of 5-7 Hz dominates on the EEG. From the 7th to the 12th month of life, the alpha rhythm is formed with a gradual decrease in the number of theta and delta waves. By 12 months, oscillations dominate, which can be characterized as a slow alpha rhythm (7-8.5 Hz). From 1 year to 7-8 years, the process of gradual displacement of slow rhythms by faster oscillations (alpha and beta range) continues. After 8 years, the alpha rhythm dominates on the EEG. The final formation of the EEG occurs by 16-18 years.

Limit values ​​of the frequency of the dominant rhythm in children

The EEG of healthy children may contain excessive diffuse slow waves, bursts of rhythmic slow oscillations, discharges of epileptiform activity, so that from the point of view of traditional assessment of the age norm, even in obviously healthy individuals under the age of 21 years, only 70-80 can be classified as “normal”. % EEG.

From 3-4 to 12 years of age, the proportion of EEG with excess slow waves increases (from 3 to 16%), and then this figure decreases quite quickly.

The reaction to hyperventilation in the form of the appearance of high-amplitude slow waves at the age of 9-11 years is more pronounced than at younger group. It is possible, however, that this is due to less clear performance of the test by younger children.

Representation of some EEG variants in a healthy population depending on age

The already mentioned relative stability of the EEG characteristics of an adult remains until approximately 50 years of age. From this period, a restructuring of the EEG spectrum is observed, expressed in a decrease in amplitude and relative amount alpha rhythm and an increase in the number of beta and delta waves. The dominant frequency after 60-70 years tends to decrease. At this age, in practically healthy individuals, theta and delta waves also appear visible during visual analysis.

Electroencephalography (EEG) is an excellent method for diagnosing epilepsy and various brain injuries. Unfortunately, EEG is often prescribed to everyone, including patients who do not need it at all.

The essence of the method

EEG is a method that records electrical signals from neurons (nerve cells in the brain). Indeed, some diseases can manifest as severe disturbances in the electrical activity of the brain.

Most often this is epilepsy, in which a group of neurons exhibits excessive activity, and structural changes in the brain (tumor, cyst, consequences of stroke and hemorrhage). Almost always, using an EEG, a doctor (neurophysiologist) can determine where this focus of excitation is located.

In our country there are diagnostic standards for all diseases. Unfortunately, in accordance with Russian standards, such an excellent method as EEG is often used to diagnose not only epilepsy and brain tumors, but also any neurological disorders.

For example, a patient complains of fainting in a stuffy room, with a crowd of many people, in a confined space. Or for a paroxysmal headache. Here are the readings for the EEG according to the standards.

Moreover, in most cases, a routine EEG is used with a recording of up to 20 minutes. Unfortunately, such a short recording often does not record even some types of epilepsy, in which changes in activity are quite pronounced. For a detailed assessment of electrical activity in epilepsy, a longer EEG recording is needed, and preferably overnight monitoring or recording after a sleepless night (sleep deprivation). And if we are talking about “vegetative-vascular dystonia” or headaches, then the EEG will most likely only confuse both the doctor and the patient.

Problems decoding results

The doctor receives the EEG report and the patient waits hopefully for the verdict. If a stroke or tumor has already been identified, then usually there is no intrigue. Even such a short recording will show that yes, indeed, there is a focus of pathological activity. The recording, in particular, will help evaluate the effectiveness of treatment for excessive neuronal activity in the affected area.

But in other cases, such as headaches or panic attacks, there may be options. Often the conclusion indicates “dysfunction of the midline structures” or “reduced threshold for convulsive readiness.”

Such a conclusion is not a diagnosis or an indication of any disease! But for the patient, this can seem like a scary find. But in fact, all these “dysfunctions” may indicate that the patient had anxiety at the time of the study or simply had a headache.

Only focal EEG changes should alert the doctor. This is a reason to prescribe an additional examination, such as magnetic resonance imaging (MRI), to exclude a tumor or cyst.

The value of EEG

It turns out that a routine 20-minute EEG often does not carry the key to diagnosis. If we are looking for a tumor, it is better to do an MRI or CT (computed tomography). If we are looking for epilepsy or assessing the effectiveness of its treatment, then it is better to do long-term EEG recording (monitoring).

EEG monitoring is a relatively expensive study, but it provides significantly more information compared to routine EEG.

In practice, it turns out that, following the diagnostic standards for such common diseases as headaches, vegetative dystonia, panic attacks, the doctor sends the patient for an EEG, sometimes guessing in advance about the results of the examination. Unfortunately, this delays making a correct diagnosis, and sometimes leads both the doctor and the patient in the wrong direction who want to deal with the “lowering the seizure threshold.”

To paraphrase a well-known aphorism, I would like to add that the doctor should treat the patient, and not examine him.

Be healthy!

Maria Meshcherina

Photo istockphoto.com

] are taken into account when diagnosing disorders and pathologies of the central nervous system. This is a study of brain functionality based on passive recording of frequency signals. What is EEG decoding, what parameters are used to perform it? What do the phrases and conclusions written in the conclusion mean? We explain it simply and in detail in this article.

Diagnosis of brain functions using EEG is based on recording signals and comparing them with indicators of bioelectrical activity of the brain (BEA) of a conditionally healthy person. Of course, there is no single sample or standard for comparison. Neurophysiologists know the normal parameters of BEA for humans different ages, there are observations for certain pathologies. Based on these data, it is possible to decipher the encephalogram, taking into account the developmental characteristics and health status of the patient.

The norm in the EEG results - what is the picture in a healthy person

The normal functioning of the brain is based on a frequency pattern of a combination of several rhythms. They have a certain localization, frequency and amplitude (maximum value), and can overlap and be suppressed by each other. For an examination, it is enough to record four types of signals, but sometimes there is a need to monitor all indicators.

Rhythms of bioelectrical activity of the brain during wakefulness

Let us briefly describe these frequency characteristics for a person in a state of normal rest, but not in sleep.

  1. Alpha rhythm is inherent in most healthy people. It is defined as a signal with a frequency of 8 to 14 Hz when the subject is in a dark room, at rest, with his eyes closed. Localized in the back of the head and closer to the crown, evenly distributed (symmetrical) across the hemispheres of the brain. When visual signals appear and thinking (problem solving) may partially fade or be blocked.

  2. The beta rhythm of brain activity manifests itself at a frequency of 13 to 30 Hz with obvious activity, attention and anxiety, and the receipt of external information. This is the rhythm of attention and activity, it is found in the frontal region of the brain. The amplitude is significantly inferior to the alpha rhythm. In a state of rest and absence of external signals, it calms down.

  3. The gamma rhythm on the encephalogram is recorded with a significant frequency range from 30 to 120-180 Hz, which is fully explained by its purpose - this frequency occurs when solving mental problems, if necessary, to concentrate, to achieve concentration. The amplitude of gamma rhythm oscillations is very small, and when it reaches a value of 15 μV, doctors talk about pathology, a sharp loss of intellectual potential, and a disorder of mental function.

  4. The kappa rhythm is interesting because it is actually a blocking signal for the alpha rhythm, when a person needs to move from a state of rest to mental work. A signal with a frequency of 8 - 12 Hz occurs in the temporal part. Its shape and frequency are such that when applied to the alpha rhythm, the latter’s oscillations fade away.

  5. The lambda rhythm or “visually active” signal of medium frequency and a very narrow range occurs in the back of the head when a person activates the connection between vision and mental activity and attention - it is maintained when solving the task of searching for an object or image and fades away when fixing the gaze. During the search period, it partially extinguishes the alpha rhythm in the visual zone.

  6. The mu rhythm signal is very similar to the alpha rhythm - it arises in the back of the head, has the same frequency range and actually maintains the alpha rhythm at rest, serving as a kind of frequency stabilizer that prevents the brain from losing balance too quickly with minor stimuli. The mu rhythm disappears as soon as any type of activity begins.

Rhythms of brain signals during sleep

In a state of sleep and transition to sleep, during blackout and coma, other BEA rhythms operate. Their appearance during wakefulness is alarming, as it is considered a sign of pathological processes, including cancer and epileptic nature.

  1. The delta rhythm occurs during deep sleep and in coma. In children, it can manifest itself both at rest and during activity, and registration of delta oscillations while an adult is awake may mean that the encephalograph has “caught” the border of the oncological process.

  2. The theta rhythm plays the role of a filtering agent, which is provoked by the hippocampus during sleep to process previously received information. Self-learning and filtering of data that the brain must process and remember depend on its stability. Its appearance outside sleep can be a sign of latent epilepsy, pre-epileptic aura.

  3. The sigma rhythm is fixed in the initial stage of sleep, during the transition between phases of sleep, when the theta rhythm changes to the delta rhythm. It is considered an important diagnostic indicator in identifying problems with sleep and attention.

Based on the recorded signals, the overall BEA indicator of the brain is derived. Next, the specialists proceed to EEG decoding according to the main features and criteria. Attention is paid to frequency and amplitude indicators, pulse modulation, smoothness of graphs, localization and symmetry of their distribution. How to understand where is the norm and where is the violation?

Before evaluating the decryption results, you need to understand. This study is functional, which means that its results can be used to judge the functioning of the brain. A full diagnosis is not made on the basis of an EEG, but it is possible to assume the presence of pathologies, confirm or exclude some disorders. This can be explained something like this: if a person has signs of epilepsy, hidden seizures, then the EEG decoding of the theta rhythm will show the frequency value even when awake. But you will have to order a series of examinations to understand what is causing the attacks - a tumor, a scar from a stroke, inflammation in a separate part of the cerebral cortex.

What is interpretation of EEG results?

Is it possible to decipher EEG results yourself? This is impossible without knowledge of neurophysiology. There are many specific factors that need to be taken into account. If such a decoding is made without taking into account individual characteristics patient, the result will be at least vague. In the worst case, you will find signs of terrible diseases, get neurosis and depression, but in reality it turns out that the result is not terrible.

What do doctors look at when deciphering encephalogram data?

After receiving the result in the form of recording signals on paper tape, the neurophysiologist studies them according to the main criteria:

  • frequency and amplitude of oscillations - deviations from the norm may be within acceptable values ​​or deviate from them;

  • the shape of the overall signal graph - it should be correct, smooth, without jumps and dips;

  • distribution of rhythms across hemispheres and zones - knowing where the reading electrode is located, you can determine the localization of a specific rhythm;

  • symmetry of signals - in most cases, uniform distribution between the hemispheres is considered the norm;

  • dependence of the rhythm on the patient’s condition - in sleep, at rest, when stimulated by light, sound, activity;

  • the presence of paroxysms - repeated short interruptions in frequency and rhythm.

Violations of the BEA of the brain in the recording are identified and recorded initially in order to subsequently determine their connection with pathologies.

Examples of violations of BEA and rhythms on the encephalogram

For alpha brain activity, pathology is considered to be a constant presence in the frontal lobes, an asymmetry between the hemispheres exceeding 35%, a non-sinusoidal graph, scatter and instability of frequency, increased and decreased amplitude. Based on the combination of signs of alpha rhythm disturbance, one can assume cancer and circulatory disorders in the brain.

Deviations in the amplitude of beta brain activity towards consistently high levels indicate the likelihood of a concussion. If spindle-shaped signals appear, encephalitis may be suspected. In children, a high amplitude of oscillations in the center and front of the brain can serve as a signal of delayed mental and mental development.

High amplitude sleep rhythms (delta and theta) indicate functional disorders. If a signal with such deviations is widely distributed throughout the brain and is recorded in all parts, then there is a high probability of severe disorders in the central nervous system.

Important! - indicators of normality and abnormalities on the EEG depend on age! Features of brain development must be taken into account when deciphering!

Decoding the encephalogram for some diseases

Specific diseases can give a well-described picture on the EEG. Thus, when taking data during an epileptic attack, you can quite accurately determine the place of its origin by the peaks on the encephalogram. During an attack, pointed waves appear especially clearly. Burst-like increases in signal amplitude may be present.

With traumatic brain injuries with minor consequences, EEG rhythms will be unstable and asymmetrical. If the pattern of rhythm disturbances increases during the week after the injury, alpha oscillations slow down, then a conclusion is drawn about the serious consequences of the injury.

Hemorrhages give a picture of a disorder of alpha waves and clearly visible flashes of the delta rhythm in a slow state. In this case, the picture may persist even after the disappearance of external signs of TBI. A desynchronized type of EEG can occur in irritative disorders and diffuse disorders of various origins.

What should not frighten the patient in deciphering the EEG?

Complex terms in EEG decoding do not always indicate real danger. You should not injure yourself with fears if a neurophysiologist has discovered an inconsistent asymmetry of signals between the hemispheres, diffuse disorganization of the alpha rhythm, moderate dysrhythmia and increased tone of the middle structures. Dysfunction of the middle structures can develop against a background of stress and is fully recoverable.

Only a doctor can interpret the EEG conclusion. And to make a diagnosis, an additional one is prescribed. When scars and tumor-like structures are detected, the picture of the vessels near them is determined using methods. Only based on the results of an encephalogram, a full diagnosis with the causes and picture of the development of the disease is not made. We should not forget that there is a set of diagnostic criteria that must converge in a certain combination - without this, the pathology is not considered confirmed.

Using the method of electroencephalography (abbreviation EEG), along with computer or magnetic resonance imaging (CT, MRI), the activity of the brain and the state of its anatomical structures are studied. The procedure plays a huge role in identifying various anomalies by studying the electrical activity of the brain.


EEG is an automatic recording of the electrical activity of neurons in brain structures, performed using electrodes on special paper. Electrodes are attached to various areas of the head and record brain activity. In this way, the EEG is recorded in the form of a background curve of the functionality of the structures of the thinking center in a person of any age.

A diagnostic procedure is performed for various lesions of the central nervous system, for example, dysarthria, neuroinfection, encephalitis, meningitis. The results allow us to evaluate the dynamics of the pathology and clarify the specific location of the damage.

The EEG is carried out in accordance with a standard protocol that monitors activity during sleep and wakefulness, with special tests for the activation response.

For adult patients, diagnosis is carried out in neurological clinics, departments of city and regional hospitals, and a psychiatric clinic. To be confident in the analysis, it is advisable to contact an experienced specialist working in the neurology department.

For children under 14 years of age, EEGs are performed exclusively in specialized clinics by pediatricians. Psychiatric hospitals do not perform the procedure on young children.

What do EEG results show?

An electroencephalogram shows the functional state of brain structures during mental and physical stress, during sleep and wakefulness. This is an absolutely safe and simple method, painless, and does not require serious intervention.

Today, EEG is widely used in the practice of neurologists in the diagnosis of vascular, degenerative, inflammatory brain lesions, and epilepsy. The method also allows you to determine the location of tumors, traumatic injuries, cyst.

EEG with the impact of sound or light on the patient helps to express true visual and hearing impairments from hysterical ones. The method is used for dynamic monitoring of patients in intensive care units in a coma state.

Norm and disorders in children

  1. EEG for children under 1 year of age is performed in the presence of the mother. The child is left in a sound- and light-proof room, where he is placed on a couch. Diagnostics takes about 20 minutes.
  2. The baby's head is wetted with water or gel, and then a cap is put on, under which the electrodes are placed. Two inactive electrodes are placed on the ears.
  3. Using special clamps, the elements are connected to wires suitable for the encephalograph. Due to the low current, the procedure is completely safe even for infants.
  4. Before monitoring begins, the child's head is positioned level so that there is no forward bending. This may cause artifacts and skew the results.
  5. EEGs are done on infants during sleep after feeding. It is important to let the boy or girl get enough immediately before the procedure so that he falls asleep. The mixture is given directly in the hospital after a general medical examination.
  6. For children under 3 years old, an encephalogram is taken only in a state of sleep. Older children may remain awake. To keep the child calm, they give him a toy or a book.

An important part of the diagnosis are tests with opening and closing the eyes, hyperventilation (deep and rare breathing) with EEG, squeezing and unclenching of the fingers, which allows disorganization of the rhythm. All tests are conducted in the form of a game.

After receiving the EEG atlas, doctors diagnose inflammation of the membranes and structures of the brain, latent epilepsy, tumors, dysfunction, stress, and fatigue.

The degree of delay in physical, mental, mental, speech development carried out using photostimulation (blinking a light bulb with eyes closed).

EEG values ​​in adults

For adults, the procedure is carried out subject to the following conditions:

  • keep your head motionless during manipulation, eliminate any irritating factors;
  • Before diagnosis, do not take sedatives or other drugs that affect the functioning of the hemispheres (Nerviplex-N).

Before the manipulation, the doctor conducts a conversation with the patient, putting him in a positive mood, calming him down and instilling optimism. Next, special electrodes connected to the device are attached to the head, and they read the readings.

The examination lasts only a few minutes and is completely painless.

Provided that the rules described above are observed, even minor changes in the bioelectrical activity of the brain are determined using EEG, indicating the presence of tumors or the onset of pathologies.

Electroencephalogram rhythms

An electroencephalogram of the brain shows regular rhythms of a certain type. Their synchrony is ensured by the work of the thalamus, which is responsible for the functionality of all structures of the central nervous system.

The EEG contains alpha, beta, delta, tetra rhythms. They have different characteristics and show certain degrees of brain activity.

Alpha - rhythm

The frequency of this rhythm varies in the range of 8-14 Hz (in children from 9-10 years old and adults). It appears in almost every healthy person. The absence of alpha rhythm indicates a violation of the symmetry of the hemispheres.

The highest amplitude is characteristic in calm state when a person is in a dark room with his eyes closed. When thinking or visual activity is partially blocked.

A frequency in the range of 8-14 Hz indicates the absence of pathologies. The following indicators indicate violations:

  • alpha activity is recorded in the frontal lobe;
  • asymmetry of the interhemispheres exceeds 35%;
  • the sinusoidality of the waves is disrupted;
  • there is a frequency scatter;
  • polymorphic low-amplitude graph less than 25 μV or high (more than 95 μV).

Alpha rhythm disturbances indicate a possible asymmetry of the hemispheres due to pathological formations (heart attack, stroke). A high frequency indicates various types of brain damage or traumatic brain injury.

In a child, deviations in alpha waves from the norm are signs of delay mental development. In dementia, alpha activity may be absent.


Normally, polymorphic activity is within the range of 25–95 μV.

Beta activity

The beta rhythm is observed in the borderline range of 13-30 Hz and changes when the patient is active. At normal indicators expressed in the frontal lobe, has an amplitude of 3-5 μV.

High fluctuations give grounds to diagnose a concussion, the appearance of short spindles - encephalitis and a developing inflammatory process.

In children, the pathological beta rhythm manifests itself at an index of 15-16 Hz and an amplitude of 40-50 μV. This signals a high probability of developmental delay. Beta activity may dominate due to the use of various medications.

Theta rhythm and delta rhythm

Delta waves appear in deep sleep and in coma. They are recorded in areas of the cerebral cortex bordering the tumor. Rarely observed in children 4-6 years old.

Theta rhythms range from 4-8 Hz, are produced by the hippocampus and are detected during sleep. With a constant increase in amplitude (over 45 μV), they speak of a dysfunction of the brain.

If theta activity increases in all departments, we can argue about severe pathologies of the central nervous system. Large fluctuations indicate the presence of a tumor. High levels of theta and delta waves in the occipital region indicate childhood lethargy and developmental delays, and also indicate poor circulation.

BEA - Bioelectric activity of the brain

EEG results can be synchronized into a complex algorithm - BEA. Normally, the bioelectrical activity of the brain should be synchronous, rhythmic, without foci of paroxysms. As a result, the specialist indicates which violations have been identified and based on this, an EEG conclusion is made.

Various changes in bioelectrical activity have an EEG interpretation:

  • relatively rhythmic BEA – may indicate the presence of migraines and headaches;
  • diffuse activity is a variant of the norm, provided there are no other abnormalities. In combination with pathological generalizations and paroxysms, it indicates epilepsy or a tendency to seizures;
  • decreased BEA may signal depression.

Other indicators in the conclusions

How to learn to independently interpret expert opinions? Decoding of EEG indicators is presented in the table:

Index Description
Dysfunction of midbrain structures Moderate disturbance of neuronal activity, characteristic of healthy people. Signals dysfunction after stress, etc. Requires symptomatic treatment.
Interhemispheric asymmetry A functional disorder that does not always indicate pathology. It is necessary to organize additional examination by a neurologist.
Diffuse alpha rhythm disorganization The disorganized type activates the diencephalic-stem structures of the brain. A variant of the norm, provided that the patient has no complaints.
Center of pathological activity Increased activity in the area under study, signaling the onset of epilepsy or predisposition to seizures.
Irritation of brain structures Associated with circulatory disorders of various etiologies (trauma, increased intracranial pressure, atherosclerosis, etc.).
Paroxysms They talk about decreased inhibition and increased excitation, often accompanied by migraines and headaches. Possible tendency to epilepsy.
Reducing the threshold for seizure activity An indirect sign of a predisposition to seizures. This is also indicated by paroxysmal brain activity, increased synchronization, pathological activity of midline structures, and changes in electrical potentials.
Epileptiform activity Epileptic activity and increased susceptibility to seizures.
Increased tone of synchronizing structures and moderate dysrhythmia They do not apply to severe disorders and pathologies. Requires symptomatic treatment.
Signs of neurophysiological immaturity In children they talk about delayed psychomotor development, physiology, and deprivation.
Residual organic lesions with increased disorganization during tests, paroxysms in all parts of the brain These bad signs are accompanied by severe headaches, attention deficit hyperactivity disorder in a child, and increased intracranial pressure.
Brain activity disorder Occurs after injuries, manifested by loss of consciousness and dizziness.
Organic changes in structures in children A consequence of infections, for example, cytomegalovirus or toxoplasmosis, or oxygen starvation during childbirth. They require complex diagnostics and therapy.
Regulatory changes Fixed for hypertension.
Presence of active discharges in any departments In response to physical exercise visual impairment, hearing loss, and loss of consciousness develop. Loads must be limited. In tumors, slow-wave theta and delta activity appears.
Desynchronous type, hypersynchronous rhythm, flat EEG curve The flat version is characteristic of cerebrovascular diseases. The degree of disturbance depends on how much the rhythm hypersynchronizes or desynchronizes.
Slowing down the alpha rhythm May accompany Parkinson's disease, Alzheimer's disease, post-infarction dementia, groups of diseases in which the brain can demyelinate.

Online consultations with specialists in the field of medicine help people understand how certain clinically significant indicators can be deciphered.

Reasons for violations

Electrical impulses ensure rapid transmission of signals between neurons in the brain. Violation of conduction function affects health. All changes are recorded in bioelectrical activity during an EEG.

There are several reasons for BEA violations:

  • injuries and concussions - the intensity of the changes depends on the severity. Moderate diffuse changes are accompanied by mild discomfort and require symptomatic therapy. Severe injuries are characterized by severe damage to impulse conduction;
  • inflammation involving the brain and cerebrospinal fluid. BEA disorders are observed after meningitis or encephalitis;
  • vascular damage by atherosclerosis. At the initial stage, the disturbances are moderate. As tissue dies due to lack of blood supply, the deterioration of neural conduction progresses;
  • irradiation, intoxication. With radiological damage, general disturbances of the BEA occur. Signs of toxic poisoning are irreversible, require treatment, and affect the patient's ability to perform daily tasks;
  • associated disorders. Often associated with severe damage to the hypothalamus and pituitary gland.

EEG helps to identify the nature of BEA variability and prescribe appropriate treatment that helps activate biopotential.

Paroxysmal activity

This is a recorded indicator indicating a sharp increase in the amplitude of the EEG wave, with a designated source of occurrence. This phenomenon is believed to be associated only with epilepsy. In fact, paroxysm is characteristic of various pathologies, including acquired dementia, neurosis, etc.

In children, paroxysms can be a variant of the norm if there are no pathological changes in the structures of the brain.


During paroxysmal activity, the alpha rhythm is mainly disrupted. Bilaterally synchronous flashes and oscillations are manifested in the length and frequency of each wave in a state of rest, sleep, wakefulness, anxiety, and mental activity.

Paroxysms look like this: pointed flashes predominate, which alternate with slow waves, and with increased activity, so-called sharp waves (spikes) appear - many peaks coming one after another.

Paroxysm with EEG requires additional examination by a therapist, neurologist, psychotherapist, a myogram and other diagnostic procedures. Treatment consists of eliminating causes and consequences.

In case of head injuries, the damage is eliminated, blood circulation is restored and symptomatic therapy is carried out. For epilepsy, they look for what caused it (tumor, etc.). If the disease is congenital, minimize the number of seizures, pain and Negative influence on the psyche.

If paroxysms are a consequence of problems with blood pressure, treatment of the cardiovascular system is carried out.

Dysrhythmia of background activity

It means irregular frequencies of electrical brain processes. This occurs due to the following reasons:

  1. Epilepsy of various etiologies, essential hypertension. There is asymmetry in both hemispheres with irregular frequency and amplitude.
  2. Hypertension - the rhythm may decrease.
  3. Oligophrenia – ascending activity of alpha waves.
  4. Tumor or cyst. There is an asymmetry between the left and right hemispheres of up to 30%.
  5. Circulatory disorders. The frequency and activity decreases depending on the severity of the pathology.

To assess dysrhythmia, indications for an EEG are diseases such as vegetative-vascular dystonia, age-related or congenital dementia, and traumatic brain injury. The procedure is also carried out when high blood pressure, nausea, vomiting in humans.

Irritative changes on EEG

This form of disorder is predominantly observed in tumors with a cyst. It is characterized by general cerebral EEG changes in the form of diffuse cortical rhythms with a predominance of beta oscillations.

Also, irritative changes can occur due to pathologies such as:

  • meningitis;
  • encephalitis;
  • atherosclerosis.

What is disorganization of cortical rhythmicity?

They appear as a consequence of head injuries and concussions, which can provoke serious problems. In these cases, the encephalogram shows changes occurring in the brain and subcortex.

The patient’s well-being depends on the presence of complications and their severity. When insufficiently organized cortical rhythms dominate in a mild form, this does not affect the patient’s well-being, although it may cause some discomfort.

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