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Amplification, recording, and analysis of the electrical activity of the brain.
Electrodes are placed on the scalp in various locations. The difference between the electric potential of two sites is recorded. The difference between one pair or among many pairs at a time can be obtained. The most frequently seen pattern in the normal adult under resting conditions is the alpha rhythm of 8.5 to 12 waves per sec. A characteristic change in the wave occurs during sleep, on opening the eyes, and during periods of concentration. Some people with intracranial disease will have a normal electroencephalogram (EEG), but others with no otherwise demonstrable disease will have an abnormal EEG. Nevertheless, the use of this diagnostic technique has proved to be very helpful in studying epilepsy and convulsive disorders and in localizing lesions in the cerebrum.
SEE: alpha rhythm; SEE: beta rhythm; SEE: theta wave