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  • Cynthia M. Johnson, MA
Publication Type:





An electroencephalogram (EEG) is a test that shows electrical activity of the brain.

Placement of Sensors for an EEG.

http://services.epnet.com/getimage.aspx?imageiid=24582458si55551220.jpgPlacement of Sensors for EEGNULLjpgPlacement of Sensors for EEGNULL\\filer01\Intellect\images\si55551220.jpgCopyright © 2002 Nucleus Communications, Inc. All rights reserved.30NULL2002-10-01255391Copyright © Nucleus Medical Media, Inc.

Reasons for Test

An EEG may be done to look for changes in brain activity after an injury or illness such as:

It may also be used to look for disorders of the brain, such as seizures .

Possible Complications

There are no major problems that can happen from having this test.

What to Expect

Problems to Look Out For

If you have had seizures, call your doctor if your seizures change after the test.

Prior to Test

Before the test, the care team may talk to you about:

  • The medicines, herbs, and supplements that you take. Some may cause problems during the test. These may need to be stopped.
  • Avoiding food or drinks with caffeine for 8 hours before the test.
  • Staying awake the night before the test—if you are having a sleep-deprived EEG.
  • Getting a ride to and from the test—if you have seizures or a sleep-deprived EEG.

Electrodes will be placed around your scalp for the test. Shampoo your hair the day of the test so that they attach better. Do not use hair styling products.

Description of the Test

Electrodes will be placed on your scalp with special gel or paste. The electrodes may also be part of a cap that is slipped over your head. They will record the brain's electrical activity. You will be asked to close your eyes and be still for most of the test. You may also need to:

  • Breathe deeply and quickly.
  • Watch fast pulses of light. This can set off a seizure in some.

A video of the test may be taken.

After the Test

The electrodes will be taken off and you will be able to go home. You may need to stay longer if you are being treated for another problem.

How Long Will It Take?

About 1 hour. The test may be done over a number of days for people in the hospital.

Will It Hurt?



A specialist will review the results. It can take a few weeks for the doctor to get the results and share them with you.





  • EEG (electroencephalogram). Kid's Health—Nemours Foundation website. Available at: http://kidshealth.org/parent/general/sick/eeg.html.
  • Schuele SU. Evaluation of seizure etiology from routine testing to genetic evaluation. Continuum (Minneap Minn). 2019;25(2):322-342.
  • Seizure in adults. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/seizure-in-adults.
  • Seizure in children. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/seizure-in-children.


  • Mark D. Arredondo, MD
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.