There are many diverse studies of the brain. Some are based on the passage of x-rays through the body, others work on the basis of a magnetic field. But these examination methods can also be used to diagnose diseases of other organs and systems. However, there is an examination method that is used specifically for the diagnosis of brain pathologies. It has received the name "electroencephalogram" (EEG), and various EEG rhythms are displayed on it.
Principle of operation
Electroencephalogram - a method for the diagnosis of brain diseases, which is based on recording potential differences between the electrodes placed on the head. On the tape, which is printed during the EEG, you can see the curved lines of different frequencies and amplitudes, called EEG rhythms.
Some rhythms are considered normal, or physiological, and some are found only in pathology. However, in children and elderly people, those rhythms that are a pathology for people of other age groups can be considered physiological.
So what does an EEG of the brain show in an adult? In essence, this examination method makes it possible to see if different departments work together in harmony and whether their nervous activity is synchronized.
Main advantages
What are the advantages of electroencephalography over other methods of diagnosing brain pathology?
- Absolute harmlessness and painlessness - absolutely has no side effects, and also does not cause discomfort.
- Safety - unlike other modern methods of diagnosing diseases of the nervous system, it has no contraindications. So, with computed tomography, the patient is exposed to x-rays, and with magnetic resonance imaging, the presence of metal objects in the body (vascular clips, pacemaker, prostheses) is contraindicated.
- Non-invasiveness - during the EEG, there is no need for injections or other violations of the integrity of the skin.
- High sensitivity - it is possible to diagnose a wide range of diseases.
Indications
What conditions can be determined using this examination method? What does an EEG of the brain show in an adult?
- The level of brain maturity in children.
- Sleep disorders, such as insomnia, inversion of sleep and wakefulness.
- Volumetric formations of the brain.
- Traumatic brain injuries.
- Epileptic activity.
- Infectious diseases of the brain (encephalitis, encephalomyelitis).
- Poisoning by poisons that are toxic to the nervous system.
- Impairment of consciousness: stupor, coma.
- A statement of brain death.
- Neurosis.
- Establishes the need for dose adjustment in the treatment of epilepsy.
For the diagnosis of diseases in which brain changes are unstable, for example, for epilepsy, it is important to record the EEG during the attack. Since in the interictal period, the EEG rhythms of a person in 40-50% are absolutely normal, which can knock down a diagnosis.
Preparation for analysis and algorithm
To prepare for the electroencephalogram, no special manipulations are required. The main thing is to tell the patient in detail about the procedure, about the algorithm of its implementation. This is especially important when conducting EEG to a child. Since a large number of wires can scare him, it is necessary to clearly explain that this procedure is absolutely safe and painless.
During the removal of the EEG, a person should be calm and relaxed.
The removal of the rhythms of the electroencephalogram is carried out in a sitting or lying position, with eyes closed. The device itself is a cap with electrodes on it, which are lubricated with a contact agent and connected to the recording part of the device.
In this case, the pulses captured by the electrodes are recorded in parallel and the patient is recorded. Thus, a convulsive attack and a change in EEG rhythms can be compared. With the help of video monitoring, it becomes possible to differentiate a real convulsive seizure from a simulation. So, if the video shows a change in the patient’s behavior, but the same activity as before is observed on the EEG, this means that the person is simulating. But options are also possible when seizures are not associated with a change in brain activity, for example, with hysterical neurosis.
EEG Characteristics
And now let's proceed directly to decoding the EEG. The main characteristic of an electroencephalogram is frequency. Of course, the human eye is not able to capture and characterize absolutely all frequencies present on the EEG tape. Therefore, they were classified according to the main frequency ranges. Each of the groups corresponds to a letter of the Greek alphabet (alpha, beta, theta, delta and gamma).
Based on the frequency range, amplitude, waveform, EEG rhythms are formed, which are also indicated by Greek letters. For example, the alpha rhythm. Each rhythm corresponds to a specific brain activity. And the rhythm consists of EEG waves.
Basic rhythms
The following basic EEG rhythms are distinguished:
- Alpha rhythm. Its characteristics: frequency - 8-12 Hz, wavelength - 75-125 ms, amplitude - 10-150 μV.
- Beta rhythm. Its characteristics: frequency - 13-30 Hz, wavelength - 40-75 ms, amplitude - 5-30 μV.
- Theta rhythm. Its characteristics: frequency - 4-7 Hz, wavelength - 130-250 ms, amplitude - 10-100 μV.
- Delta rhythm. Its characteristics: frequency - 3-4 Hz, amplitude - several hundred μV.
- Gamma rhythm. Its characteristics: frequency - 1-3 Hz.
Alpha rhythm
The main rhythm, which is recorded in 90% of adults. Most pronounced in the occipital region of the brain. It is best visualized while awake, with eyes closed, in a room with the lights off. With the appearance of mental activity or with tension of attention, the amplitude (height) of the rhythm decreases.
The presence of amplitude heterogeneity is characteristic, it either rises or decreases. A so-called "spindle" is formed.
Beta rhythm
EEG beta rhythm is also observed during wakefulness. Most pronounced in the frontal regions of the brain. Unlike alpha waves, the amplitude of the beta rhythm increases dramatically with mental activity and spreads to other parts of the brain. So, with the activation of attention, especially visual, with emotional and mental stress, the height of beta waves increases sharply.
Theta rhythm
This EEG rhythm is most clearly visualized in children of preschool age and in mentally unbalanced persons with a tendency to aggression and with difficult adaptation in society. With an increase in mental activity, the amplitude of theta waves increases.
Delta rhythm
This rhythm consists of delta waves, which have the largest amplitude among all the waves in the electroencephalogram. This rhythm occurs in violation of human consciousness, both in deep sleep and in drug intoxication. In addition, the presence of delta waves is characteristic of a coma.
Also, with the help of visualization of this rhythm, it is possible to determine the approximate localization of the traumatic focus or tumor, since this rhythm appears in areas located on the border with brain damage.
Pathological rhythms
The above lists the EEG rhythms that a person has normally, depending on the different conditions of the brain. However, there are special rhythms that can occur only with pathology:
- peaks - with a duration of 10-75 ms and an amplitude of 10-100 μV;
- sharp waves - with a duration of 75 ms, an amplitude of 20-200 μV, having a wide base and pointed peaks;
- spikes - lasting less than 10 ms.
EEG for epilepsy
As noted above, electroencephalography is used in the diagnosis of many diseases of the brain. However, in most cases, changes in the EEG are nonspecific. For example, in order to differentiate a tumor from a brain injury, in addition to EEG, it is necessary to carry out additional imaging methods (computed tomography, magnetic resonance imaging).
But there is a disease in the diagnosis of which the EEG has not lost its relevance in comparison with more modern methods of examining the brain - epilepsy. In addition, this method allows not only to make a diagnosis, but also to determine the localization of the epileptic focus and the type of epilepsy.
The high-amplitude peak waves noted in the section above are the most characteristic sign of epilepsy on the EEG. They suddenly appear at the onset of a seizure attack and also suddenly disappear after an attack. Here, video monitoring, which makes it possible to compare EEG data with the clinical picture, is of particular value.
During epilepsy, the peak – slow wave and peak – fast wave complexes are also noted. They are manifested by the alternation of waves of different frequencies and amplitudes.
Stimulating signals are widely used in cases of suspected epilepsy: hyperventilation (a series of deep slow breaths and exhalations), a blinking bright light. These tests help reveal latent epileptic activity that is not displayed in calm.
EEG monitoring of sleep
Using electroencephalography, it is possible to determine the phases of sleep and wakefulness even in a child in the womb from the 28th week of pregnancy.
Separate the fast and slow phases of sleep. When recording sleep, much attention is paid to the movements of the eyeballs and muscle activity, which are recorded in parallel with brain activity. According to these data, sleep is also divided into REM and Non-REM.
Non-REM sleep is divided into the following stages:
- The first stage continues until a person falls asleep. Its duration is up to 10 minutes. It is characterized by a slow rotation of the eyeballs, the presence of theta waves on the EEG is predominant.
- The second stage is light sleep. Muscles are relaxed, eyeballs do not move. The theta rhythm is visualized on the electroencephalogram, there are waves characteristic of this stage only: K-complexes and sleep spindles. In time, this phase takes about half of all sleep.
- The third and fourth stages are slow sleep, or deep sleep. In the phase of deep sleep, a person sleeps hardest. Eyeballs do not move. On the electroencephalogram, high-amplitude delta waves are observed. When the delta rhythm exceeds half of the entire EEG tape, the transition of the third stage to the fourth begins. The duration of the first period of the deep sleep phase is from 30 to 40 minutes.
REM sleep consists of only one phase. It is during REM sleep that a person sees vivid, catchy dreams. This stage is characterized by the rotation of the eyeballs, short-term muscle contractions, increased respiration and palpitations. The electroencephalogram consists of alpha and beta waves. The duration of this phase is about 20% of the total sleep period.
Where can I do an EEG?
We have already examined how it is necessary to prepare for the analysis, which conditions are indications for its analysis. In addition, it was found out how the EEG is deciphered, and what rhythms are inherent in a person with different brain activity. Now it’s worth talking about where you can make an EEG.
EEG is available in a number of laboratories and private clinics in Russia, as well as in some state neuropsychiatric dispensaries.
Among the laboratories, EEG diagnostics is presented in Invitro, EEG Lab is a neurophysiological laboratory in Moscow.
Among private clinics, the opportunity to have an EEG is available at the She Medical Center, the Doctor Anna Family Clinic, and the Cardio-Neurological Center.
It can be concluded that although the electroencephalogram is not the most modern and sensitive method for diagnosing brain diseases, its absolute safety and accessibility ensure its widespread use in medical practice. And the use of EEG in the diagnosis of diseases accompanied by convulsive seizures, and completely displaces the effectiveness of all other examination methods!