Electroencephalography is a method of research of the electrical activity of the brain. The method is based on the principle of registration of electric potentials that appear in nerve cells in the process of their activity. The electrical activity of the brain is small, it is expressed in ppm volts. The study of brain potentials is therefore using a special, highly sensitive measuring instruments and amplifiers, called an electroencephalograph (Fig). With this purpose on the surface of the skull are superimposed metal discs (electrodes)that connect the cables to the input of the electroencephalograph. At the outlet of the obtained a graphic image on paper oscillations of a difference of brain bioelectric called an electroencephalogram (EEG).


Data EEG be different in healthy and sick person. At rest on EEG adult healthy person visible rhythmic fluctuations of bioelectric potentials of the two types. Larger fluctuations, with an average frequency of 10 per 1 sec. and with a voltage equal to 50 UV, called alpha waves. Other, smaller fluctuations, with an average rate of 30 per 1 sec. and a voltage equal to 15-20 Macs are called beta waves. If the human brain goes from a state of relative peace to a state of activity, the alpha-rhythm is weakening, and beta-rate increases. During sleep like alpha-rhythm and beta-rhythm and decrease appear slower biopotentials with frequency or 4-5 2-3 fluctuations in 1 sec. and frequency 14-22 fluctuations in 1 sec. In children EEG differs from the results of research into the electrical activity of the brain in adults and approaching them as full maturation of the brain, that is, 13 - 17 years of life.
At various diseases of the brain EEG there are a variety of disorders. Signs of pathology at the EEG rest are persistent lack of alpha-activity (desynchronization of alpha-rhythm) or, conversely, a sharp intensifying (hypersynchronous); violation of the frequency of oscillations of biopotentials; and the emergence of pathological forms of biopotentials - slow-amplitude (theta and Delta waves, sharp waves, complexes peak-wave and paroxysmal discharge and so on, For these violations neuropathologist can determine the severity and to some extent the nature of brain diseases. For example, if in the brain have a tumor or there is bleeding in the brain, electroencephalographic curves give the doctor an indication, where (in which part of the brain) is damage is. When epilepsy on EEG even in megprobalja period one can observe the emergence on the background of normal bioelectric activity sharp waves or complexes peak-wave.
Especially important electroencephalography when it comes to having the brain surgery to remove a patient's tumor, abscess, or a foreign body. Data electroencephalography in combination with other methods of research used by outlining a plan for future operations.
In all cases, when during examination of the patient with diseases of the Central nervous system from a physician-neurologist suspect about structural lesions of the brain, it is advisable electroencephalographic study, With this purpose it is recommended to refer the patients in institutions where there are rooms of electroencephalography.

Electroencephalography (gr. enkephalos - brain, grapho - write) - method research activity of a brain of the person and animals by studying electrical activity of various departments.
Experimental work has shown that under the influence of various external stimuli in the brain occur electrical oscillations. The so-called spontaneous fluctuations, i.e. fluctuations of biopotentials, not associated with a put irritation, for the first time revealed the I. M. Sechenov in 1882 in the brain frogs. In 1913-1925, V.V. Pravdic-Nemensky using a string galvanometer found in dogs in bioelectric brain activity in a number of rhythmic processes.
In 1929 Berger (N. Berger), using a string galvanometer, registered bioelectric activity of the cerebral cortex of the human brain. Demonstrating the possibility to take bioelectric activity from undamaged surface of the head, he opened the prospects of using this method for examination of patients with disorders of the brain activity. However, the electrical activity of the brain is very weak (the amount of biopotentials in average 5-500 MACs).
Further development of these studies and their application became possible after creation, amplification of electronic equipment. It gave the opportunity to receive a significant increase of biopotentials, and because of its businessconnect allowed to observe oscillations without distortion of their form (see Electronic amplifiers).