Electroencephalogram (EEG)

Explanation of the test

This painless procedure is a test that measures the electrical activity of the brain (brainwaves). The test shows areas of the brain that are not functioning correctly either because of too little or too much electrical activity.

The pattern (brainwaves) produced by the brain is displayed on a computer screen and is used to check for seizures and other brain problems. The brain produces a different pattern awake, during drowsiness and during sleep. Thus, you will be asked to close your eyes and relax during the test so that you can fall asleep for a period of 10 to 15 minutes.

After measuring your head and marking the spots where the electrodes will be applied, the technologist will ask you to lie down on a comfortable bed. These spots will be rubbed with a sandy preparation to remove oil and 22 small metal discs (electrodes) will be attached to your scalp with non-allergenic electrode cream. These electrodes are connected by wires to the EEG machine. At the conclusion of the test, the technologist will remove the cream from your scalp with warm water.

Total test time is approximately 90 minutes. Patients are requested to get half their normal sleep the night before so that they are tired enough to sleep during the test. Depriving someone of sleep can cause changes in the electrical activity of the brain. Recording these changes on the EEG can provide doctors with important information.


  • Hair washed with shampoo (no conditioners applied) night before or day of test.
  • Hair must be dry
  • No caffeine day of the test (coffee, cola beverages)
  • Half of your normal period of sleep the night before (no more than 4 hours)
  • if the test is ordered with "sleep deprivation", stay awake the entire night before

General information

  • Total testing period is approximately 90 minutes
  • You should continue to take your regular medications, unless told to do otherwise by your physician
  • There is no radiation or (x-ray) involved with this test.
  • Any further questions about how the test is performed should be asked of the technologist when you arrive for the test or you can call the Neurodiagnostics Department at 773-665-3195
  • Your doctor will receive the final results after a neurologist interprets the test, usually within 3 business days.
  • If you are unable to keep your appointment please call Central Scheduling at 773-665-3060. If you will be late, call Neurodiagnostics at 773-665-3195.
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