Deciphering the EEG parameters of the brain

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Deciphering the EEG parameters of the brain

EEG (electroencephalography) of the brain is a highly informative method for diagnosing the state of the central nervous system, based on recording the bioelectric potentials of the cerebral cortex during its life. The results of the study are recorded on paper tape or displayed on a computer monitor. The neurophysiologists of the Yusupov hospital are deciphering the results of the EEG of the brain in adults using a computer program.

The patient receives the conclusion on the second day. If the results of EEG decoding are interpreted ambiguously, they are discussed at a meeting of the expert council with the participation of professors and doctors of the highest category.

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Indications for an EEG study

If, according to the results of the EEG study, the patient does not need medical correction, neurologists observe him in dynamics, perform repeated studies, conduct EEG video monitoring of day and night sleep, and use other methods of neuroimaging .

An electroencephalogram provides an opportunity to:

assess the nature and degree of brain dysfunction;

establish the side and location of the pathological focus;

to study the change of sleep and wakefulness;

clarify the results of other types of diagnostics (computed tomography), when the patient has signs of damage to the central nervous system, and other research methods do not reveal a structural defect;

monitor the effectiveness of drugs;

determine in which parts of the brain epileptic seizures begin;

evaluate how the brain works between seizures;

establish the causes of fainting, panic attacks crises.

EEG is performed in the presence of the following indications:


insomnia, impaired sleep quality;

sleep disorder (walking, talking in a dream);

nocturnal sleep apnea;

seizures without an established cause;

endocrine diseases;

vascular pathology of the brain;

traumatic brain injury;

inflammatory diseases of the central nervous system.

With frequent headaches, vegetovascular dystonia, dizziness, an EEG is also performed. The study is indicated for patients who constantly feel tired, have suffered a stroke or microstroke, neurosurgical surgery.

Contraindications and preparation for EEG

There are no absolute contraindications for electroencephalography. If the patient has seizures, is ill with coronary heart disease, arterial hypertension, suffers from mental disorders, an anesthesiologist is present during the EEG procedure at the neurology clinic of the Yusupov hospital. He provides emergency assistance in case of non-standard situations.

Eat 2 hours before the procedure. The EEG is carried out in a calm state, so it is impossible to worry and be nervous during the study. If the doctor needs to detect seizure activity in the brain, he will suggest that the patient get some sleep before the study. It is not recommended to get to the medical institution while driving. EEG is not performed in patients with signs of an acute respiratory viral infection. The study is not contraindicated for children and pregnant women. During pregnancy, EEG is performed without functional tests.

EEG norm in adults

The interpretation of the EEG results consists of three sections:

description of the leading types of activity and graphic elements;

conclusion after description with interpreted pathophysiological materials;

correlation of indicators of the first two parts with the clinical picture of the disease.

The main descriptive term in EEG is “activity”. It evaluates any sequence of waves. The main types of activity that are recorded during the study and subsequently subjected to decoding, as well as further study, are the frequency, amplitude and phase of the waves. The frequency is estimated by the number of wave oscillations per second. It is expressed in units of measurement – hertz (Hz). In the description, the neurophysiologist indicates the average frequency of the studied activity.

On the EEG, the main rhythms of the brain are determined:

delta – from 0.3 to 4 Hz;

theta – from 4 to 8 Hz;

alpha – from 8 to 13 Hz;

low-frequency beta rhythm – from 13 to 25 Hz;

high-frequency beta rhythm – from 25 to 35 Hz;

beta – from 35 to 50 Hz.

Rhythms correspond to types of activity. On the EEG, you can see special types of bioelectrical activity of the brain:

flat EEG;

high-frequency asynchronous low-amplitude (“double”) activity;

low-amplitude slow polymorphic activity;

polyrhythmic activity.

Pathological images of the electroencephalogram include:

spike ;

slow spike ;


sharp wave.

Normally, the alpha rhythm predominates in the occipital regions of the brain. It decreases in amplitude from the back of the head to the forehead. In the frontal regions, it is not recorded with bipolar leads from electrodes that are applied along sagittal lines with small interelectrode distances. Symmetric in amplitude and frequency in the left and right hemispheres. On a normal EEG, functional asymmetry is observed with a predominance in filling of the surface facing the bones of the skull, and a slight excess of the amplitude is greater in the right hemisphere of the brain. This is a consequence of the functional asymmetry of the brain. It is associated with greater activity of the left hemisphere.

pathologically altered brain

Pathological manifestations on the EEG are slow rhythms – theta and delta. The lower their frequency and the higher the amplitude, the more pronounced the pathological process. Slow -wave activity appears in the following pathological processes:

dystrophic diseases;

demyelinating and degenerative lesions of the brain;

compression of brain tissue;

liquor hypertension;

the presence of some lethargy, deactivation phenomena, a decrease in the activating effects of the brain stem.

High-frequency rhythms (beta-1, beta-2, gamma rhythm) are also a criterion for pathology. Its severity is the greater, the more the frequency is shifted towards high frequencies and the more the amplitude of the high-frequency rhythm is increased. The high-frequency component of the EEG occurs when the structures of the brain are irritated (irritation of the brain centers).

Electrical rhythms of the brain

The concept of “rhythm” on the EEG is considered to be a type of electrical activity that refers to a certain state of the brain and is coordinated by the corresponding mechanisms. When deciphering the indicators of the EEG rhythm of the brain, neurophysiologists take into account its frequency corresponding to the state of the brain area, amplitude and characteristic changes during functional changes in activity.

A separate category of types of rhythms that manifest themselves in sleep conditions or in pathological conditions includes 3 varieties of this indicator:

the delta rhythm is determined in comatose patients and in the phase of deep sleep, it is recorded when recording signals from areas of the cerebral cortex located on the border with areas affected by malignant neoplasms;

theta rhythm has a frequency interval within 4–8 Hz, manifests itself during sleep, is responsible for the qualitative assimilation of information, and underlies self-learning;

The sigma rhythm has a frequency of 10–16 Hz, is considered one of the most noticeable and main oscillations of the spontaneous electroencephalogram, and occurs during natural sleep at its initial stage.

Based on the results obtained when recording the EEG, an indicator is determined that characterizes a complete comprehensive assessment of the waves – the bioelectric activity of the brain. The doctor of functional diagnostics checks the EEG parameters – frequency, rhythm and the presence of sharp flashes that provoke characteristic manifestations. On these grounds, the neurophysiologist makes a final conclusion.

EEG brain monitoring in children

There are several methods for recording EEG in children:

daytime EEG – the first study, which consists in a short-term recording of brain biopotentials with the performance of functional tests ( photostimulation and hyperventilation to detect hidden changes;

EEG with deprivation (sleep deprivation) is performed when the routine EEG is not informative ;

long-term (continued) EEG with registration of daytime sleep is performed if there is a suspicion of the presence of paroxysms or the likelihood of changes in the EEG during sleep;

EEG of nocturnal sleep allows you to record changes in the EEG during wakefulness before falling asleep, in a state of drowsiness, during the actual nocturnal sleep and awakening.

EEG monitoring is accompanied by video recording with the ability to record in complete darkness and the connection of additional sensors. All devices used by neurophysiologists at the Yusupov Hospital are expert-class equipment and, in accordance with Federal Law No. 102-FZ “On Ensuring the Uniformity of Measurements”, undergoes regular verification of metrological characteristics.

In order to prepare a child for an EEG during sleep, doctors recommend:

on the day of the study, wake up the baby 1.5 – 2 hours earlier than the usual wake-up time and during the day, without letting him sleep, play active games with him;

limit the amount of liquid you drink, eating sweets, pickles and spicy foods;

after 18.00 play only quiet calm games;

walk outdoors in a quiet place;

exclude TV viewing, computer and video games.

The study is carried out in a room isolated from light and sound stimuli. The recording is made on an autonomous block in which the memory card is located. The study is synchronously recorded on a hard disk for evaluation, printing of significant fragments and recording individual fragments on a mobile data carrier.

Deciphering EEG indicators in an adult

In order to decipher the EEG and provide accurate results, not to miss any of the smallest manifestations on the record, neurophysiologists take into account all the important points that may affect the parameters under study, such as:

patient’s age;

the presence of certain diseases;

possible contraindications.

Upon completion of the collection of all EEG data and their processing, the doctor of functional diagnostics analyzes and forms a final conclusion, which provides for making a further decision on the choice of the method of therapy. Any disturbance of activities can be a sign of diseases caused by certain factors.

EEG disorders are considered:

permanent fixation of the alpha rhythm in the frontal lobe;

permanent violation of wave sinusoidality;

the presence of frequency spread;

excess of the difference between the hemispheres up to 35%;

amplitude below 25 µV and over 95 µV.

When a high amplitude of the delta rhythm is detected, a neurophysiologist can assume the presence of a volumetric formation of the brain. The overestimated values of theta and delta rhythm, which are recorded in the occipital region, indicate a violation of the circulatory function, inhibition, and a delay in the development of the child.

Deciphering the EEG of the brain in children

EEG in children has features. The EEG record of a premature baby born at 25–28 weeks of gestation looks like a curve in the form of slow flashes of delta and theta rhythms, which are periodically combined with sharp wave peaks 3–15 seconds long with a decrease in amplitude to 25 μV. In full-term newborns, these values are divided into 3 types of indicators:

when awake (with a periodic frequency of 5 Hz and an amplitude of 55–60 Hz);

in the active phase of sleep (with a stable frequency of 5–7 Hz and a fast low amplitude);

during restful sleep with flashes of delta oscillations at high amplitude.

During 3-6 months of a baby’s life, the number of theta oscillations is constantly growing. The delta rhythm is characterized by a decline. From 7 months to one year, the alpha waves form in the child, and the delta and theta gradually fade away. Over the next 8 years, slow waves on the EEG are constantly replaced by fast alpha and beta oscillations. Until the age of 15, alpha waves predominate. By the age of 18, the formation of the biological activity of the brain is completed.

In order to undergo an examination and decipher the results of the EEG, call the Yusupov hospital. The contact center is open 24/7 every day. Neurophysiologists analyze the EEG in dynamics, compare the results of the study with the EEG norm.

Night video EEG monitoring

Video EEG monitoring is the only objective method for diagnosing many diseases of the central nervous system. With the help of research, neurologists determine specific disturbances in the initial phase of the EEG recording during an attack. The system allows you to conduct a long examination. The following information is synchronously written to the hard disk:

EEG recording on a digital electroencephalograph;

physiological signals of the body through polygraphic channels;

audio information from two microphones;

video information from two video cameras;

markers reflecting certain events that the doctor notes during the recording.

EEG night monitoring, the cost of which in Moscow is from 1200 rubles, is carried out in the following cases:

if necessary, confirm the diagnosis of epilepsy;

to clarify the form of epilepsy and the localization of epileptic foci;

In order to confirm the medical remission of an epileptic disease and the sufficiency of the ongoing antiepileptic treatment;

to resolve the issue of the abolition of antiepileptic therapy;

with paroxysmal disorders of consciousness and paroxysmal movement disorders;

to clarify the cause of a single epileptic seizure;

in order to clarify the cause of rare seizures (incorrect diagnosis, incomplete compensation);

with recurrence of seizures against the background of constant medication.

Nighttime EEG video monitoring is performed with speech delay of unknown origin, progressive decline in cognitive functions, minimal brain dysfunction. The study should be done in patients suffering from affective-respiratory paroxysms, febrile convulsions, disorders of day and night sleep. Indications for night video EEG monitoring are:

enuresis, encopresis (bedwetting of urine and feces);

bettolepsy (transient disturbances of consciousness occurring at the peak of a coughing fit);

non-epileptic paroxysms (night terrors, narcolepsy, sleepwalking);

paroxysms of dizziness of an unclear nature that occur without objective symptoms.

Video EEG monitoring (the price depends on the duration of the procedure) is performed by neurophysiologists for myoclonus and similar conditions: sleep myoclonus, autonomic myoclonus , opsoclonus ( dancing eye syndrome), benign infantile myoclonus .

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