Definition

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:

    
  • Trauma
  • Coma
  • Brain infection— encephalitis
  • Electrolyte imbalance
  • 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.

    Results

    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.