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Alternative Names
electroencephalogram , brain wave test

An EEG is a graphic record of the electrical activity of the brain

Who is a candidate for the test?
The EEG is used to evaluate sleep disorders and to determine the causes of periods of unconsciousness. An EEG is also used to diagnose seizure disorders, confusion, brain tumours, head injuries, degenerative diseases, and metabolic or chemical disturbances that affect the brain. An EEG may also be used to monitor cerebral blood flow during surgical procedures, such as carotid endarterectomy.

How is the test performed?
First, the patient lies down. Then, the doctor or technician places a number of small electrodes on the scalp over different regions of the brain. The electrodes carry information about the brain's electrical activity to an amplifier. A special machine records the amplified brain waves and 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.

What is involved in preparation for the test?
People may ask their doctors for special instructions.

What do the test results mean?
A normal reading shows brain waves at a normal frequency, amplitude, and other characteristics of normal brain function. An abnormal EEG may indicate any of the following:
  • seizure disorders
  • brain tumour
  • brain infection
  • head injury
  • bleeding, or haemorrhage
  • narcolepsy, which is a type of sleep problem
  • cerebral, or brain, death
  • cerebral infarct or stroke, which is dead brain tissue resulting from loss of blood supply
Author: David T. Moran, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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