Electroencephalography (EEG) is a bio-medical technique use to measure and record minute electrical currents generated by the brain. 

A German psychiatrist named ‘Hans Berger of ‘Coburg’ is known as the inventor of Electroencephalography. 

How EEG works?

Our brain is not quiet; it constantly generates minute electrical currents even during sleep and in a deep coma. These electrical pulses are recorded from the skull’s surface utilizing small wires (electrodes) attached to the scalp. In normal persons, they have an electrical potential of about 100 microvolts. To monitor and record the electrical activitydoctors use a machine that has about 20 equally spaced electrodes. Each electrode is represented by letters and numbers. The numbers indicate the side of the head so that odd numbers are on the left side and even numbers are on the right; they are attached on the scalp’s surface following the standard positions adopted by the International Federation of Electroencephalography


The position of the electrodes is carefully measured so that recording of the subsequent brain activity can be compared with the earlier ones. The electrodes are connected to a differential amplifier which is particularly useful at recording and displaying very small electrical signals. The amplifier amplifies the voltages to 1,000,000 times. The current then moves on an electromagnetic pen that makes a graph on a chart paper.

In the normal adult person, most of the Electroencephalography recordings are made up of rhythmic oscillating waves regularly repeated at about 10Hertz ( Hertz is the unit of frequency). They are called alpha waves. 

Maximum alpha waves can be obtained in a person from their back of the central nervous system (brain) when they are in a relaxed position with their eyes closed. But when the eyes are opened the waves disappear or are gets blocked.

Electroencephalography normally reveals the more rapid rhythmical movement. It consists of smaller waves called beta waves, that are repeated at 18-25 hertz. Beta waves are related to the function of sensory-motor parts of the brain.

During sleep, the central nervous system cells generate even higher voltage electrical waves, but they are slowed down to 2 or 3 hertz. During coma also very feeble waves are recorded.

The slowest waves with high amplitude that arise from the localized area of brain damage are called delta waves. They are linked with deep sleep.

Rhythmic slow waves at frequencies between 4 and 7 Hertz ( slightly faster than delta waves) are called theta waves. Slow waves suggest abnormality in adults but not in infants or young children. EEG patterns are not always constant; it gradually changes in the growing child until he has attained the age of 8 to 12 years. At this age, adult patterns appear.



EEG uses

Every person has a different EEG pattern. Identical twins have almost identical patterns.

Electroencephalography has proved to be very useful for studying the working of the brain. It has proved helpful in detecting many brain diseases.


Electroencephalography can also give indications about the abnormalities of the brain. It can also detect Epilepsy and abnormal metabolic conditions. ‘Coma’ conditions can be studies from Electroencephalography. If we get a flat EEG, it indicated the ‘brain’s death’.



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