The human brain is a complex structure. It is here that centralization of nervous activity is carried out, all impulses coming from the sensory organs are processed, and response signals are formed to perform one or another action.
Sometimes it happens that the brain begins to function improperly. It is not easy to suspect the presence of a pathological focus in the brain. Conventional diagnostic methods, such as ultrasound, MRI, do not always give a proper idea of his work. In such cases, it is necessary to take an electroencephalogram - a snapshot of the brain. The study of the formation of brain waves is engaged in electroencephalography. What it is?
What is this method?
Electroencephalography is currently understood to mean a specific section of electrophysiology, which studies the electrical activity of the brain and its individual parts. Measurement is carried out using special electrodes applied to the scalp in various places. Electroencephalography of the brain is capable of recording the slightest changes in the activity of nerve cells, which puts it an order of magnitude higher than other methods for diagnosing neurological diseases.
As a result of recording brain activity, a “snapshot” or curve is formed - an electroencephalogram. On it you can determine all areas of brain activity, which is manifested by certain waves and rhythm. It is customary to designate these rhythms with the letters of the Greek alphabet (at least 10 such rhythms are distinguished). Each of them contains certain waves that characterize the activity of the brain or its specific area.
History of the study
A study of the electrical activity of the brain was begun in 1849, when it was proved that it, like a muscle or nerve fiber, is capable of generating electrical impulses.
In 1875, two independent scientists (Danilevsky in Russia and Caton in England) were able to provide data on the electrophysiological activity of the brain in animals (the study was conducted on dogs, rabbits and monkeys).
The basics of electroencephalography were laid in 1913, when Vladimir Vladimirovich Pravdich-Neminsky was able to record the first electroencephalogram from the brain of a dog. He was the first to propose the term “electrocerebrogram”.
For the first time in humans, an encephalogram was recorded in 1928 by the German scientist Hans Berger. He proposed renaming the term into an electroencephalogram, and the method itself was widely used since 1934, when the presence of Berger's rhythm was confirmed.
How is the procedure performed?
Registration of biopotentials from the brain is performed using an apparatus called an electroencephalograph.
Normally, the biocurrents formed by the brain are rather weak, and it is difficult to fix them. And in this case, electroencephalography comes to the rescue. What it is was mentioned above. With the help of an electroencephalograph, these potentials are fixed and amplified when passing through the apparatus.
Potentials are fixed due to electrodes located on the surface of the head.
The received signal can either be recorded on paper or stored electronically (computer-based electroencephalography) for subsequent research.
The recording itself is made with respect to the so-called zero potential. Usually, either the earlobe or the mastoid process of the temporal bone, which do not emit biocurrents, is usually taken.
Pulse registration is carried out by electrodes placed on the surface of the head according to special schemes. The most common pattern is 10-20.
Scheme 10-20
This circuit is standard when placing electrodes. They are distributed on the scalp in the following sequence:
- First of all, the line connecting the bridge of the nose and the occipital protuberance is determined. It is divided into 10 equal segments. The first and last electrodes are superimposed respectively on the first and last, tenth, parts of the line. The other two electrodes are installed relative to the first two electrodes at a distance equal to 1/5 of the length formed at the beginning of the line. The fifth is placed in the middle between the already installed ones.
- Another line is conditionally formed between the external auditory canals. The sensors are installed two on each side (on each hemisphere) and one on the top of the head.
- In parallel to the midline between the nape of the neck and the nose, there are 4 more lines - the right and left parasagital and temporal. They pass through electrodes mounted along the ear line. Electrodes are also installed along these lines (5 on the parasagittal, and 3 on the temporal).
A total of 21 electrodes are mounted on the surface of the head.
Interpretation of the results
Typically, computer electroencephalography involves recording the results on a computer to create a database of each patient. As a result of fixing the obtained data, rhythmic oscillations of two types are formed. Conventionally, they are called alpha and beta waves.
The former are usually fixed at rest. They are characterized by a voltage of 50 μV and a certain rhythm - up to 10 per second.
The electroencephalography of sleep is based on the determination of beta waves. Unlike alpha waves, they are smaller in size and occur when awake. Their frequency is about 30 per second, and the voltage is in the region of 15-20 μV. These waves usually indicate normal activity of the brain while awake.
Clinical electroencephalography is based precisely on the fixation of these waves. Any deviation of them (for example, the appearance of alpha waves in the wakeful state) indicates the presence of any pathological process. In addition, the appearance of pathological waves — theta waves, peak waves — or a change in their nature — the appearance of peaked complexes, is possible on the EEG.
Features of the study
A prerequisite for the study is the immobility of the patient. When performing any activity on the electroencephalogram, interference occurs that further interferes with the correct interpretation. In children, the presence of such interference is inevitable.
In addition, electroencephalography itself has its difficulties in children. What it is to explain to the child is quite difficult, and it is not always possible to persuade him to wear a helmet with electrodes. It can cause a sense of panic in children, which will necessarily distort the results. That is why parents should be warned that they need to somehow persuade the baby to wear electrodes.
During the study, tests are usually performed with hyperventilation and photostimulation. They allow you to identify some disturbances in the brain that are not fixed at rest.
Before the study, it is not recommended, and sometimes forbidden, to use any medications that affect the brain.
Indications for the procedure
In what cases is this study recommended?
The method of electroencephalography is shown in the following cases:
- If there is a history of spontaneous fainting.
- For a long time, headaches that do not stop with taking medications.
- With impaired memory and attention.
- Sleep disturbances and problems falling asleep and waking up.
- If you suspect a mental retardation of children in development.
- Dizziness and fatigue.
In addition to the above, electroencephalography allows you to control the results of treatment in patients receiving a particular type of drug or physiotherapy.
The method allows you to determine the presence of diseases such as epilepsy, brain tumors, infectious lesions of the brain tissue, trophic disorders and blood supply to the brain tissue.
Electroencephalography in children is carried out in the diagnosis of Down syndrome, with cerebral palsy, mental retardation.
Contraindications to the procedure
The procedure itself has practically no contraindications for use. The only thing that can limit its conduct is the presence on the head surface of extensive injuries, acute infectious processes or postoperative sutures that did not heal at the time of the study.
Brain electroencephalography is carried out with caution in mentally violent patients, as the appearance of the apparatus can infuriate them. To pacify such patients, it is necessary to introduce tranquilizers, which significantly reduce the informational content of the procedure and lead to incorrect data.
If possible, the procedure should be abandoned for severe patients with decompensated disorders of the cardiovascular system. If a portable electroencephalograph is available, then it is better to use it, rather than taking the patient to the diagnostic room.
The need for research
Unfortunately, not everyone knows that there is such a diagnostic method as electroencephalography. What it is - even fewer people know, because of which not everyone goes to the doctor about its conduct. But in vain, because this method is quite sensitive when registering the potentials of the brain. With a well-conducted study and the corresponding decoding of the obtained data, it is possible to get an almost complete idea of the functionality of the brain structures and the presence of a possible pathological process.
It is this technique that allows us to determine the presence of a lag in mental development in young children (although you should definitely make an allowance for the fact that the brain potentials in children are slightly different from those in adults).
Even if there are no disorders on the part of the nervous system, it is sometimes better to conduct a diagnostic examination with the mandatory inclusion of EEG in it, as it can help determine the beginning changes in the structure of the brain, and this is usually the key to the success of the cure of the disease.