Epilepsy: Electroencephalogram (EEG)

• What is an EEG?
• How do I prepare for an EEG?
• What happens during the EEG?
• What happens after the test?

What is an EEG?

An EEG, or electroencephalogram, is a test that can help diagnose epilepsy. During an EEG, the electrical signals of the brain are recorded. This electrical activity is detected by electrodes, or sensors, placed on the patient's scalp and transmitted to a polygraph that records the activity.

How It Works

Electrical signals produced by the brain neurons are picked up by the electrodes and transmitted to a polygraph, where they produce separate graphs on moving paper using an ink writing pen or on a computer screen.

How Do I Prepare For an EEG?

To prepare for your EEG you should:

• Discuss any medications you are taking with your physician prior to your procedure.
  
  
• Wash your hair the night before the test. Do not use hair cream, oils or spray afterward.

What Happens During the EEG?

You lie down on the examining table or bed while about 20 electrodes are attached to your scalp. You are asked to relax and lie first with your eyes open, then later with them closed. You may be asked to breathe deeply and rapidly or to stare at a flashing light - both of these activities produce changes in the brain-wave patterns. If you are prone to seizures, it is rare that you may experience one during the test. If you are being evaluated for a sleep disorder, EEG may be performed continuously during the night while you are asleep. Such a recording, which may involve an evaluation of other body functions during sleep, such as respiration and pulse, is referred to as polysomnography.

What Happens After the Test?

The electrodes are removed and the glue that held them in place is washed away with acetone. You may have to use additional acetone at home to completely remove the glue. Unless you are actively having seizures or are restricted by your physician, you may drive home. If the EEG was performed overnight, you should arrange to have someone drive you home. If you stopped taking anticonvulsant drugs for the EEG, you can usually start taking them again.

A neurologist examines the EEG recording for abnormalities in the brain-wave pattern, which may reflect diseases of the nervous system.

Reviewed by the doctors at The Cleveland Clinic Neuroscience Center.

Edited by Joseph R Carcione, MBA, DO on February 01, 2007

Portions of this page © The Cleveland Clinic 2000-2005