Electroencephalography - what is it? How is electroencephalography performed?

The human brain is a complex structure. It is here that the centralization of nervous activity is carried out, all impulses coming from the sense organs are processed and responses are formed for the performance of an action.

Sometimes it happens that the brain begins to function incorrectly. To suspect the presence of a pathological focus in the brain is not easy. The usual methods of diagnosis, such as ultrasound, MRI, do not always give a proper idea of his work. In such cases it is necessary to carry out the removal of the electroencephalogram - a picture of the brain. The study of brain wave formation deals with electroencephalography. What it is?

What is this method?

Electroencephalography is currently understood as a specific branch of electrophysiology, which studies the electrical activity of the brain and its individual parts. Measurement is performed using special electrodes applied to the scalp in various places. Electroencephalography of the brain is able to detect slight changes in the activity of nerve cells, which puts it an order of magnitude higher than other methods of diagnosing neurological diseases.

As a result of recording the activity of the brain, a "snapshot" or a 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 denote these rhythms by the letters of the Greek alphabet (they sing out at least 10 such rhythms). Each of them contains certain waves that characterize the activity of the brain or a certain part of it.

History of the research

The study of brain electrical activity was started in 1849, when it was proved that he, 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 measurements of 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 dog's brain. He also first proposed the term "electrocerebrogram."

For the first time in human encephalogram was recorded in 1928 by the German scientist Hans Berger. He proposed to rename the term into an electroencephalogram, and the method itself became widespread since 1934, when the presence of the Berger rhythm was confirmed.

How is the procedure performed?

Registration of biopotentials from the brain is performed using a device called the electroencephalograph.

Normally, 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 by electrodes located on the surface of the head.

The resulting signal can either be recorded on paper, or stored electronically (computerized electroencephalography) for later investigation.

The record itself is made with respect to the so-called zero potential. It is usually taken either by earlobe, or mastoid process of the temporal bone, which do not emit biocurrents.

The pulses are recorded by electrodes placed on the surface of the head according to special schemes. The most widely used scheme is 10-20.

Scheme 10-20

This scheme is standard when placing electrodes. They are distributed on the scalp in the following sequence:

• First of all, a line connecting the bridge of the nose and the occiput is determined. It is divided into 10 equal segments. The first and last electrodes are superimposed on the first and last, tenth, parts of the line, respectively. The other two electrodes are positioned relative to the first two electrodes at a distance equal to 1/5 of the length of the line formed at the beginning. The fifth is placed in the middle between the already established ones.
• Conditionally, another line is formed between the external auditory canals. The sensors are installed two on each side (for each hemisphere) and one - on the vertex.
• Parallel to the median line between the occiput and the bridge of the nose there are 4 more lines - right and left parasagital and temporal. They pass through the electrodes installed along the "ear" line. According to the lines, more electrodes are installed (5 - on the parasaggital, and 3 - on the temporal).

In total, 21 electrodes are installed on the surface of the head.

Interpretation of the results

Usually, computerized 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 first are usually fixed in a state of rest. They are characterized by a voltage of 50 μV and a certain rhythm - up to 10 per second.

Electroencephalography sleep is based on the definition of beta waves. In contrast to waves of alpha nature, they are smaller in size and occur in a state of wakefulness. Their frequency is about 30 per second, and the voltage is around 15-20 microvolts. These waves usually indicate normal brain activity in the waking state.

Clinical electroencephalography is based precisely on the fixation of these waves. Any deviation (for example, the appearance of alpha waves in a state of wakefulness) indicates the presence of some pathological process. In addition, on the encephalogram may appear pathological waves - theta waves, peak waves - or a change in their nature - the appearance of spiky complexes.

Features of the study

A prerequisite for the study is the immobility of the patient. In the performance of an activity on the electroencephalogram, interference occurs, which further interferes with proper decoding. In children, the presence of such interference is inevitable.

In addition, it has its own difficulties in carrying out in children and the electroencephalography itself. What it is - to explain to the child is difficult enough, and it is not always possible to persuade him to wear a helmet with electrodes. It can cause a feeling of panic in children, which will necessarily distort the results. That's why you should warn your parents that you need to persuade your child to put electrodes in any way.

During the study, samples with hyperventilation and photostimulation are usually performed. They allow us to identify certain disorders in the brain that are not fixed at rest.

Before the study is not recommended, and sometimes it is 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 an anamnesis of spontaneous fainting.
• For a long time, there are headaches that can not be stopped by taking medication.
• In case of memory and attention violation.
• Sleep disorders and problems with falling asleep and awakening.
• When suspected of mental retardation of children in development.
• Dizziness and fatigue.

In addition to the above, electroencephalography allows you to monitor the results of treatment in patients who receive some form of drug or physiotherapy.

The method allows to determine the presence of such diseases as epilepsy, brain tumors, infectious lesions of the brain tissue, trophic disorders and blood supply to the brain tissue.

Electroencephalography in children is performed in the diagnosis of Down's syndrome, with cerebral palsy, mental retardation.

Contraindications to the procedure

The procedure itself has practically no contraindications to the application. The only thing that can limit its conduct is the presence on the surface of the head of extensive injuries, acute infectious processes or postoperative sutures that did not heal by the time of the study.

Electroencephalography of the brain with caution is carried out in mentally violent patients, since the appearance of the apparatus can lead them into a rage. To suppress such patients, it is necessary to administer tranquilizers, which significantly reduce the informative nature of the procedure and lead to incorrect data.

If possible, the procedure should be abandoned for severe patients with decompensated cardiovascular disorders. If there is a portable electroencephalograph available, then it is better to use it, and not to take the patient himself to the diagnostic room.

Necessity of research

Unfortunately, not everyone knows that there is such a method of diagnosis as electroencephalography. What it is - knows even fewer people, because of what not everyone turns to a doctor about his conduct. But in vain, because this method is quite sensitive when registering the potentials of the brain. With a correctly conducted study and corresponding interpretation of the obtained data, it is possible to obtain a practically complete idea of the functionality of brain structures and the existence of a possible pathological process.

It is this technique that makes it possible to determine the presence of a backwardness in mental development in young children (although it is necessary to make an amendment to the fact that the potentials of the brain in children differ somewhat from those of adults).

Even if there are no abnormalities from the nervous system, it is sometimes better to perform a diagnostic examination with the mandatory inclusion of an EEG, as it can help determine the beginning changes in the structure of the brain, which is usually the key to the success of curing the disease.