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The brain cells talk to each other and to the rest of the body with electrical signals. An electroencephalogram (EEG) is a test that will show the electrical activity of the brain.

Placement of Sensors for an EEG

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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 diagnose or rule out disorders of the brain such as seizures.

Possible Complications

There are no major complications associated with this test.

What to Expect
Prior to Test

Certain foods, medication, or activity can affect your brain activity. Before the test:

  • You may need to stop certain medications before the test.
  • You may be asked to avoid caffeine for eight 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.

If you have had seizures, make sure to have a ride available 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. The electrodes will record the brain's electrical activity. You will be asked to close your eyes and be still for most of the test. Depending on the reason for the test, there may be other steps such as:

  • Breathing deeply and rapidly.
  • Watching a strobe light with fast pulses of light. This can set off a seizure in some.

In some cases, a video recording of the test will be made.

After Test

The electrodes will be taken off and you will be able to go home. If you are being treated for a condition you may need to stay in the hospital longer.

How Long Will It Take?

The test may take about one hour.

An EEG may also be done over a number of days for people that are in the hospital with severe illnesses.

Will It Hurt?

No. The EEG electrodes sit on top of the skin and are painless.


Your test results will be reviewed by a specialist. Your doctor will get a report within 1-2 weeks and will talk to you about the results.

Call Your Doctor

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


Epilepsy Foundation

National Institute of Neurological Disorders and Stroke


Canadian Neurological Sciences Federation

Epilepsy Canada


EEG (electroencephalogram). Nemours Kid's Health website. Available at: Updated September 2013. Accessed February 13, 2014.

Seizure in adults. EBSCO DynaMed Plus website. Available at: Updated April 11, 2016. Accessed October 10, 2016.

Seizure in children. EBSCO DynaMed Plus website. Available at: Updated April 11, 2016. Accessed October 10, 2016.

Shevell M, Ashwal S, et al. Practice parameter: Evaluation of the child with global developmental delay: Report of the Quality Standards Subcommittee of the American Academy of Neurology and The Practice Committee of the Child Neurology Society. Neurology. 2003;60:367-380.

Last reviewed March 2017 by EBSCO Medical Review BoardRimas Lukas, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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