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U-M Health SystemThis information is approved and/or reviewed by U-M Health System providers but it is not a tool for self-diagnosis or a substitute for medical treatment. You should speak to your physician or make an appointment to be seen if you have questions or concerns about this information or your medical condition.
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EEG (Electroencephalogram)

What is an EEG?

An EEG (electroencephalogram) is a test that records the electrical activity of your brain. (The nerve cells in your brain work by carrying tiny electrical charges.)

When is it used?

An EEG can help your healthcare provider diagnose medical problems such as epilepsy, sleep apnea, encephalitis (infection in the brain), dementia, and brain tumors. This test is sometimes used during surgery to check the effect of anesthesia. It may be used to test for brain death in cases of severe injury or illness.

How do I prepare for an EEG?

Your head doesn't need to be shaved for an EEG. Some EEG labs ask that your hair be clean and free of hair products such as hairspray or mousse. Ask your provider if there are any special instructions you need to follow. Also ask if there are any substances or medicines that you should avoid before the test.

Sometimes a sedative is given just before the test to help you relax during the EEG. In case this happens, plan to have someone drive you home after the test.

What happens during the test?

An EEG is painless and normally takes 45 minutes. During the test you will relax in a reclining chair or bed. Small metal plates (electrodes) are pasted or taped to your head. The electrodes send information to a machine that records brain waves on paper.

EEGs may be done while you are:

  • sleeping
  • resting with your eyes closed
  • resting with your eyes open
  • breathing rapidly (and just after)
  • looking at a flashing light.

The EEG records how the brain responds to these changes.

If your healthcare provider suspects you have epilepsy, an EEG will usually be done while you are sleeping. You may be given a medicine to help you sleep.

What happens after the test?

You can usually go home as soon as the test is done. Ask your heath care provider when and how you will get the result of your test.

What are the benefits of this test?

This test helps your healthcare provider diagnose certain medical conditions.

What are the risks associated with this test?

There are no risks. Discuss any concerns you have with your healthcare provider.

When should I call my healthcare provider?

Call your provider right away if you have any change or worsening of your symptoms.

Call during office hours if:

  • You have questions about the test or its result.
  • You want to make another appointment.
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Last modified: 2006-10-10
Last reviewed: 2008-05-30
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
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