The EEG: Electroencephalogram Test

University of Iowa Department of Neurology
Peer Review Status: Internally Peer Reviewed
Creation Date: Unknown
Last Revision Date: June 2000

An EEG is a recording of the electrical activity in your brain. Electrodes are attached to your head so that this electrical activity can be measured and recorded. The test is used to help evaluate the health of the brain and to diagnose nervous system disorders.

What is it?

• evaluates the health of your brain and to diagnose nervous system disorders
• evaluates the electrical patterns of your brain to determine if there is abnormal electrical activity
• your EEG may be performed while you are awake or while you are asleep

How long does it take?

• 1/2 hour

Why is an EEG performed?

• if you are experiencing blackouts or spells of various nature, seizures, headaches, depression, a sleep disorder, dizziness, problems with memory, or weakness of arms and legs

Does it hurt?

• no. You will not experience any pain or discomfort
• the EEG is NOT a shock treatment
• the EEG is not an intelligence test. It cannot tell what you are thinking. Nothing is put into or taken out of your brain

What is a "Sleep" EEG?

• because the brain's electrical activity differs depending on whether you are asleep or awake, an EEG recorded while you are sleeping can be very informative, especially when seizures or any type of spell is suspected

What should you do to prepare for the test?

• wash your hair. Do NOT use any sprays, oils, or dressing of any kind
• eat normal meals
• continue taking prescribed medicaions unless your doctor gives other instructions
• if you have a "sleep" EEG, you may be asked to sleep less the night before the test, and to bring someone with you to the lab to drive you home.

How is it performed?

• you will recline in a comfortable chair and asked to remain very still
• a soft, red pencil will mark areas where electrodes will be glued on your scalp
• some special jelly is applied to each electrode
• each electrode is checked with a meter to ensure proper functioning
• lie very still and close your eyes. At certain times, you may be asked to open and close your eyes, and to breathe deeply for about three minutes
• for one part of the test, a strobe light will temporarily flash on and off. You may be given a sedative to help you relax and sleep.

After the test

• the electrodes are removed with acetone, which dissolves the glue and leaves your hair and skin intact
• you may return to your hospital room or home, unless given other instructions from your doctor
• you may wash your hair
• if you have been given a mild sedative, you should be driven home by a relative or friend
• you will learn the test results either from the doctor before you leave, or from a copy of the letter sent to your personal physician