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Electroencephalogram

(EEG)

Definition

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

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

Prior to Test

Before the test:

  • Talk to your doctor about the medicines, herbs, and supplements that you take. Some may cause problems during the test. These may need to be stopped.
  • Do not eat food or swallow drinks with caffeine for 8 hours before the test.
  • If you are having a sleep-deprived EEG, you may need to stay awake the night before the test.

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.

People who have seizures should arrange for a ride to and from the test.

Description of Test

You will be asked to sit in a chair or lie on a bed. 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 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?

The test will take about 1 hour. People who are in the hospital may have the test done over a number of days.

Will It Hurt?

No. The EEG electrodes sit on top of the skin and do not cause pain.

Results

The results will be reviewed by a specialist. It will take 1 to 2 weeks for the doctor to get the results and share them with you.

Call Your Doctor

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

RESOURCES:

Epilepsy Foundation
http://www.epilepsyfoundation.org

National Institute of Neurological Disorders and Stroke
http://www.ninds.nih.gov

CANADIAN RESOURCES:

Canadian Neurological Sciences Federation
http://www.cnsfederation.org

Epilepsy Canada
http://www.epilepsy.ca

REFERENCES:

EEG (electroencephalogram). Kid's Health—Nemours Foundation website. Available at: http://kidshealth.org/parent/general/sick/eeg.html. Accessed April 6, 2020.

Gavvala JR, Schuele SU. New-Onset seizure in adults and adolescents: a review. JAMA. 2016;316(24):2657-2668.

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. Updated February 4, 2020. Accessed April 6, 2020.

Seizure in children. EBSCO DynaMed website. Available at:https://www.dynamed.com/condition/seizure-in-children. Updated August 9, 2018. Accessed April 6, 2020.

Last reviewed February 2020 by EBSCO Medical Review Board Rimas Lukas, MD  Last Updated: 4/6/2020