Electroencephalography( EEG) - Causes, symptoms and treatment. MF.
Electroencephalography( EEG) is a method for studying the functional state of the brain based on recording its bioelectrical activity through undamaged head covers. The first record of cerebral biocurrents was made in 1928 by Hans Berger. The electrical activity of the brain, generated in the cortex, synchronized and modulated by the thalamus and reticular activating structures is recorded on the EEG.Registration of bioelectric potentials of the brain and their graphic representation by a photographic method or by ink recording are performed by a special device - by the electroencephalograph .
How is electroencephalography( EEG) performed?
A special cap with electrode-antennas connected to the device is put on the person's head. Signals coming from the cerebral cortex are transmitted to the electroencephalograph, which converts them into a graphic image( waves).This image resembles a heart rhythm on an electrocardiogram( ECG).
During registration of brain biocurrents, the patient is in a chair in a comfortable position( reclining).At the same time, he should not:
a) be under the influence of sedatives;
b) to be hungry( in a state of hypoglycemia);C) be in a state of psychoemotional arousal.
Indications for EEG
Electroencephalography is used for all neurological, mental and speech disorders. According to EEG data, one can study the cycle "sleep and wakefulness", establish the side of the lesion, the location of the lesion, evaluate the effectiveness of the treatment, and monitor the dynamics of the rehabilitation process. A great importance of EEG is in the study of patients with epilepsy, since only an electroencephalogram can reveal the epileptic activity of the brain.
Electroencephalogram decoding
The recorded curve, reflecting the nature of the brain biocurrents, is called the electroencephalogram( EEG).
The electroencephalogram reflects the total activity of a large number of brain cells and consists of many components. Analysis of the electroencephalogram allows you to identify waves on it that are different in form, constancy, periods of oscillation and amplitude( voltage).The electroencephalogram( EEG) of a healthy person has characteristic features: rhythmic activity with a frequency of about 10 Hz and an amplitude of 50 - 100 μV-alpha rhythm is allocated from all areas of the cortex. On the electroencephalogram( EEG), other rhythms are also recorded: the lower ones are delta and theta( 2 - 4, 5 - 7 Hz) and higher-beta rhythms( 13 - 30 per second), but the amplitude in their norm is low and they are overlapped by alpha-vibrations.
In a healthy adult who is at rest, the EEG usually reveals:
a) alpha waves that are characterized by a frequency of 8-13 Hz and an amplitude of 30-100 μV, they are symmetrical, sinusoidal, better expressed with the patient's eyes closed,predominantly defined in the occipital parietal region;these waves increase and decrease spontaneously and usually disappear quickly when the patient concentrates attention or opens his eyes;B) Beta waves with a frequency of oscillations greater than 13 Hz( usually 16-30) and amplitude up to 15 μV; on normal electroencephalograms they are symmetrical and are especially characteristic for the frontal region;
c) delta waves having a frequency of 0.5-3 Hz and an amplitude of up to 20-40 μV;d) theta waves with a frequency of 4-7 Hz and with an amplitude in the same range.
The electroencephalogram( EEG) changes when the functional state changes. For example, when you go to sleep, slow oscillations become dominant, and the alpha rhythm disappears. With a strong excitation against the background of alpha-rhythm disturbance, sharp changes are revealed: they manifest themselves in the intensification of slow oscillations, sometimes of beta-rhythms, violation of regularity and frequency of alpha rhythm. These and other changes have a nonspecific character.
With pronounced alpha activity, the delta and theta rhythms in a healthy adult are practically not noticeable, since they overlap with a more pronounced alpha-rhythm amplitude. However, with the depression of the alpha rhythm, which usually occurs when the patient is excited, as well as in a drowsy state and in shallow sleep( the first and second stages), the delta and theta rhythm on the EEG are manifested, and their amplitude can increase respectively to 150 and 300 microvolts. With deep sleep( the third stage), the slowest activity is recorded on the EEG as much as possible. Slow waves often appear in the form of diffuse, less often local( in the zone of the pathological focus in the brain), rhythmic oscillations forming into "flares".The level of wakefulness affects the character of the EEG. Normally, in a sleeping adult, the rhythm of bioelectrical activity is symmetrical, with slow waves appearing in amplitude and sleeping spindles in the parietal zones. Any orientation reaction to external influences is reflected in the EEG of a healthy person in the form of a temporary flattening of the curve. Emotional-mental excitement is usually accompanied by the appearance of rapid rhythms.
During the transition from infancy to adulthood, the character of the normal
EEG is gradually changing. In early childhood, it reflects mainly slow fluctuations, which are gradually replaced by more frequent ones, and by the age of 7 alpha rhythm is formed. Completely the process of evolution of the EEG is completed by 15-17 years, acquiring at this age the features of the EEG of an adult. At the age of more than 50-60 years, the normal EEG differs from that in young people by a decrease in the frequency of delta rhythm, a violation of its regulation and an increase in the number of theta waves.
When the significance of pathological activity on the EEG of an adult waking person is theta and delta activity, as well as epileptic
activity.
Especially significant EEG examination is found in the detection of epileptic activity indicating a predisposition to convulsive conditions and manifested by the following symptoms:
1) acute waves( peaks) - oscillation of a potential having a steep rise and steep decline, while the sharpness of the wave usually exceeds the amplitude of backgroundfluctuations with which they are combined;acute waves can be single or group, are detected in one or many leads;
2) peak-wave complexes, representing potential oscillations, consisting of an acute wave( peak) and a slow wave accompanying it;with epilepsy these complexes can be single or follow one another in the form of series;3) paroxysmal rhythms - rhythms of oscillations in the form of flares of high amplitude of different frequency, paroxysmal rhythms of theta and delta oscillations or slow waves of 0.5-1.0 Hz are common.
According to the EEG data, it is possible to distinguish diffuse brain damage from a local pathological process, to establish the side and to a certain extent the localization of the pathological focus, to differentiate the superficial pathological focus from the deep, to recognize the coma and its degree of severity;identify focal and generalized epileptic activity.
Special opportunities for provocative tests contribute to the expansion of EEG capabilities in determining the functional state of the brain and some of its pathological conditions, especially epileptic activity: npoba with hyperventilation - deep respiratory movements at a frequency of 20 per minute leading to alkalosis and narrowing of the brain vessels, a sample with a light stimulus- photostimulation with the help of a powerful light source( strobe), a test with a sound stimulus. So, the patient's reactions to photostimulation inspire confidence that the subject at least perceives light. If the reaction to photostimulation is absent in one hemisphere, then one can judge that on its side there is a disruption of the conduction of visual impulses from the subcortical centers to the cortical part of the visual analyzer. If photostimulation-provokes the appearance of pathological waves on the EEG, one must think about the presence of increased excitability of cortical structures. At the same time, longer photostimulation can provoke the appearance of true convulsive discharges on the EEG, and with particularly high readiness for convulsive conditions, sometimes distinct myoclonic twitching of the muscles of the face, neck, shoulder girdle, and hands that can pass into generalized true muscle cramps( photoparoxysmal reaction).
The informative value of the electroencephalogram is increased if it is recorded in a patient in a state of sleep.
With the help of the EEG, information on the functional state of the brain is obtained at different levels of the patient's consciousness. The advantage of this method is its harmlessness, painlessness, non-invasiveness.
Electroencephalography has found wide application in the neurological clinic. Especially significant are the EEG data in the diagnosis of epilepsy, it is possible their specific role in the recognition of intracranial localization tumors, vascular, inflammatory, degenerative diseases of the brain
, coma. EEG with the use of photostimulation or stimulation by sound can help differentiate true and hysterical disorders of vision and hearing or the simulation of such disorders. EEG can be used for monitoring patient monitoring. The absence of signs of bioelectric activity of the brain on the EEG is one of the most important criteria for his death.
In neurosurgical institutions during the operation, in the presence of indications, biocurrents can be recorded from the exposed brain - electrocorticography. Sometimes, in the conditions of a neurosurgical operation, an electroencephalogram is recorded using electrodes immersed in the brain. The use of computers or specialized spectrum analyzers allows automatic EEG processing, which enables the
to reveal the quantitative characteristics of its frequency composition. The possibility of a compressed spectral analysis of the EEG based on the computerized transformation of the primary EEG to the power spectrum of a fast Fourier transformer makes it possible to evaluate the EEG quantitatively, to present it in a more visual form, since the spectrograms reflect the power or amplitude of the frequency components of the EEG for a givena period of time( epoch), which makes it possible to determine the ratio of the power of different EEG rhythms and to identify those frequencies that are not detected by simple analysisrhenium curve EEG, and thus improve information content of the survey results.
Top-selective mapping of brain electrical activity. In the process of analyzing the 16-channel EEG, it is possible to transform the results of the survey into a numerical form in the form of a spectrum of power of the electrogenesis of the cortex of the cerebral hemispheres. Then the received data are presented by
in the form of a power distribution map of various types of electrical brain activity. On the map, the features of the electrical activity of
in different parts of the cerebral cortex are reproduced in conventional color, and in black and white - in the form of shading;with each value of power( coherence) corresponds to its color or density of hatching.
Electroencephalography makes it possible to objectively assess the severity of EEG asymmetry, the presence of both generalized and focal changes in brain electrical activity that are manifested directly during the EEG study.
Electroencephalography( EEG) with CCT
With the development of CT and MRI diagnostics, electroencephalography( EEG) has lost its role in the objectification of local brain lesions. However, it remained indispensable for assessing the functional state of the brain in different periods of severe TBI.
In the acute period of mild toadail TB, abnormal abnormalities are noted mainly in the form of irregularity of the alpha-rhythm and intensification of frequent oscillations with rapid reverse development of pathological changes in the electroencephalogram( EEG).
The most severe local changes, against a background of also grossly expressed cerebral changes, are detected with massive cortical-subcortical foci of contusion. Pathological changes in these cases tend to increase during the first 5-7 days.
In the acute period with epidural hematomas, there are often no significant cerebral changes;focal are of the nature of delimited slow waves or local inhibition of alpha rhythm.
With subdural hematomas, the changes in the electroencephalogram( EEG) are diverse, characterized by significant general cerebral changes: general inhibition of activity, the presence of polymorphic delta waves in deceleration, decrease and disorganization of the alpha rhythm, manifestation of slow-wave "stem" type bursts. Focal changes are characterized by vastness, fuzzy delimitation. Often, only interhemispheric asymmetry is revealed without a clear focus.
With intracerebral hematomas on the electroencephalogram( EEG), pronounced cerebral delta-theta waves manifest themselves. Focal changes in the projection zone of the hematoma - in the form of the predominance of slow waves. Of particular importance for the assessment of the condition and prognosis is electroencephalography( EEG) in severe CCT, accompanied by a prolonged coma. In these observations, changes in the electroencephalogram( EEG) are diverse and depend on the severity of the trauma, the presence and localization of foci of concussion and intracranial hematomas.
A phase change in the electroencephalogram( EEG) is typical for patients who undergo severe trauma with a reversible course. At the initial stage - a polyrhythm with the predominance of slow forms of activity, less often - a decrease in the amplitude of oscillations. Typically, the presence of a sigma-rhythm( 13-15 Hz), characteristic for normal sleep, bilateral theta waves or low-frequency alpha-rhythm, acute waves against the background of delta-oscillations. Interhemispheric asymmetry is manifested, reactivity to stimuli is weakened. Stem flares of slow waves are noted. In the future, when the coma comes out after a phase of general decline in activity, a gradual recovery of activity.
In severe TBT, which ended lethal, against the background of deep impairment of consciousness and vital functions on the electroencephalogram( EEG), slow activity from slow waves to beta-waves( alpha-coma, beta-coma) dominates, characterized by monotonicity, reactivity to stimuli, includingnumber of painful, smoothed regional differences. Focal slow waves in the zone of concussion or bruising do not appear. Typically, the predominance of the theta rhythm of low frequency( 5 Hz), indicating a complete blockade of cortical activity and the dominance of regulation from the stem and subcortical systems of the brain.
In the long-term period, CCT electroencephalography( EEG) allows the determination of epileptic activity. Pathological features of the electroencephalogram( EEG), as a rule, persist for a longer period than clinical symptoms. The recovery rate of the electroencephalogram( EEG) depends on the severity of the injury. The most persistent changes in the electroencephalogram( EEG) are in the zone of contusion foci or the former hematoma. In these areas of the brain, epileptic activity is often formed.
Changes in the electroencephalogram( EEG) in the long-term period of penetrating CCT may be manifested to a large extent over many years. They are of a general cerebral character, which is due to the development of hemo- and liquorodynamics, which have developed by this time, and are manifested by local changes( epileptic or slow activity) in the zone of primary brain damage.