What is an Electroencephalogram-EEG?

            An instrument called electroencephalograph is used to record the electrical activity of the brain. Electroencephalography is a bio-medical process of recording minute electric currents produced by the brains of human beings and other animals. This was discovered by Hans Berger of Jena now in East Germany in 1929, and found to have important clinical significance in the diagnosis of brain diseases.


            The brain constantly generates feeble electrical currents, even during sleep and in deep coma. These can be recorded from the surface of the skull by means of small wires electrodes attached to the scalp. In normal persons, there is an electrical potential of about 100 microvolt’s. So to make such recording doctors use a machine that has about 20 equally spaced electrodes, which are attached on the scalp’s surface in accordance with the standard positions adopted by the international federation of EEG? Electrode positions are measured so that subsequent recordings for the same person can be compared with the earlier ones. The electrodes are connected to an amplifier, which amplifies the voltages 1,000,000 times. The current runs an electromagnetic pen that makes a graph on a roll of chart paper.

            In a normal adult person, most of the EEG recordings are made up of rhythmic oscillating waves regularly repeated at about 10 Hertz (hertz is the unit of frequency). They are called alpha waves. They are best obtained from the back of the central nervous system brain when a person is in a relaxed position with the eyes closed. The waves disappear or are blocked when the eyes are opened.

            Normally EEG reveals more rapid rhythmical movement. It consists of smaller waves called beta waves, which are repeated at every 18-25 hertz. These are related to the function of sensory motor part of the brain. During sleep, the central nervous system cells generate electrical wave’s f eve higher voltage but they re slowed down to 2 or 3 hertz. During coma, very feeble waves are produced.

            The irregular slow waves, one to three per seconds, which arise form the localized area of the damaged region of the brain, are called delta waves. Rhythmic slow waves with frequencies between 4 and 7 hertz are called theta waves. Slow waves suggest some abnormally in case of adult but it is not so in infants or young children. EEG patterns change gradually in the growing child until he has attained the age of 8 to 12 years. That is when the adult patterns appear. Every person has a different EEG pattern. Identical at twins have identical pattern.

            EEG has proved to be very useful for studying the working of the brain and detecting many brain diseases. A doctor can figure out the working of a person’s brain by looking at the pattern of the graph. The graph also shows whether the brain is functioning properly or not.

            EEG provides indications about any abnormalities in the brain. It can be used to detect epilepsy and abnormal metabolic conditions. Coma conditions can be studied from EEGs. If we get a flat EEG, it indicates brain death. Nowadays, CAT computerized axial tomography scanning is more frequently used, as it has been found to be more useful than EEG. Better than IAT is MRI magnetic resonance imaging which gives better information of brain disorders.