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Epilepsy Health Center

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Epilepsy and the Electroencephalogram (EEG)

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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 machine that records the activity.

Electrical signals produced by the brain neurons are picked up by the electrodes and transmitted to a machine, where they produce separate graphs on moving paper recorded in ink or on a computer screen.

Recommended Related to Epilepsy

Understanding Seizures -- the Basics

A seizure occurs when there’s abnormal electrical activity in the brain. Seizures may go virtually unnoticed. Or, in severe cases, they may produce a change or loss of consciousness and involuntary muscle spasms called convulsions. Seizures usually come on suddenly and vary in duration and severity. A seizure may be a one-time event, or you may have seizures repeatedly. Recurrent seizures are called epilepsy, or a seizure disorder. Less than one in 10 people who has a seizure develops epilepsy. Experts...

Read the Understanding Seizures -- the Basics article > >

How Do I Prepare For an EEG?

To prepare for your EEG you should:

  • Discuss any medications you are taking with your doctor 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?

During an 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 may 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, the EEG may be performed 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 an EEG?

When the EEG is done, 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 doctor, 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.

WebMD Medical Reference

Reviewed by Richard Senelick, MD on July 14, 2014
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