Electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain by using sensors (electrodes) attached to the head. The computer records your brain's electrical activity on the screen or paper as wavy lines.

Certain conditions, such as seizures, can be detected by observing changes in the normal pattern of the brain's electrical activity.


An electroencephalogram (EEG) may be done to:

  • Diagnose epilepsy and determine what type of seizures are occurring. EEG is the most useful and important test in confirming a diagnosis of epilepsy.
  • Identify the location of a suspected brain tumor, inflammation, infection (such as encephalitis or meningitis), bleeding, head injury, or disease in the brain, such as Parkinson's disease.
  • Evaluate periods of unconsciousness or dementia.
  • Help predict a person's chance of recovery after a change in consciousness.
  • Confirm or rule out brain death in a person who is in a coma.
  • Study sleep disorders, such as narcolepsy.
  • Monitor brain activity while a person is receiving general anesthesia during surgery.

How To Prepare

Before the day of the electroencephalogram (EEG) test, tell your doctor if you are taking any medications. Your doctor may advise you to stop taking certain medications (such as sedatives and tranquilizers, muscle relaxants, sleeping medications, or medications used to treat seizures) before the test. These medications can affect your brain's usual electrical activity and produce abnormal test results.

Avoid foods that contain caffeine (such as coffee, tea, cola, and chocolate) for at least 8 hours before the test. Eat a small meal shortly before the test, because low blood sugar (hypoglycemia) may produce an abnormal test.

Since the electrodes are attached to your scalp, it is important that your hair be clean and free of sprays, oils, creams, lotions, and other hair preparations. Shampoo your hair and rinse with clear water the evening before or the morning of the test. Do not apply any hair conditioners or oils after shampooing.

To detect certain types of abnormal electrical activity in the brain, you may have to be asleep during the recording. As a result, you may be asked not to sleep at all the night before the test or to reduce your sleep time to 4 or 5 hours by going to bed later and getting up earlier than usual. If your child is going to be tested, try to keep him or her from taking naps just before the test. If you know that you are going to have a sleep-deprived EEG, plan to have someone drive you to and from the test.