An EEG, or electroencephalogram, is a recording of the electrical waves in the brain. It measures electrical impulses that are sent between nerve cells.

Who is a candidate for the test?

The healthcare provider may order an EEG to investigate the cause of these symptoms:

An EEG may be used to monitor blood flow to the brain during surgery on the carotid arteries. It is also used to determine brain death in a person who is in a coma.

How is the test performed?

An EEG uses small electrodes to measure the electrical activity within the brain. It does not deliver any electricity of its own. The technician will use a paste to attach 23 small electrodes to the person's scalp. The electrodes carry information about the brain's electrical activity to an amplifier. A special machine records the amplified brain waves. It produces a pattern of tracings called an electroencephalogram. During the recording, the patient may be asked to breathe deeply or to look at a flashing light.