EEG

Overview & Description

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:

amnesia

confusion

dizziness

fainting

headaches

seizures

staring or other attention problems

unusual behavior

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.

Preparation & Expectations

What is involved in preparation for the test?

Instructions for an EEG usually include the following preparation.

Avoid caffeine for 24 hours before the EEG.

Eat normally and take all prescribed medications.

Limit or avoid smoking for 24 hours before the test.

Shampoo the night before the EEG. Do not apply hair spray or gel.

Results and Values

What do the test results mean?

A normal EEG does not necessarily rule out abnormalities in the brain. However, the following conditions may be detected on an EEG:

Alzheimer's disease, a form of dementia

brain death

brain infection

brain tumors

chemical disturbances that affect the brain

degenerative neurological diseases

epilepsy

head injury

intracerebral hemorrhage, or bleeding into the brain

learning disabilities

metastasis, or spread, of cancer to the brain

sleep disorders

stroke