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Electroencephalogram (EEG)

An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain. Special sensors (electrodes camera.gif) are attached to your head and hooked by wires to a computer. The computer records your brain's electrical activity on the screen or on paper as wavy lines. Certain conditions, such as seizures, can be seen by the changes in the normal pattern of the brain's electrical activity.

Why It Is Done

An electroencephalogram (EEG) may be done to:

  • Diagnose epilepsy and see what type of seizures are occurring. EEG is the most useful and important test in confirming a diagnosis of epilepsy.
  • Check for problems with loss of consciousness or dementia.
  • Help find out a person's chance of recovery after a change in consciousness.
  • Find out if a person who is in a coma is brain-dead.
  • Study sleep disorders, such as narcolepsy.
  • Watch brain activity while a person is receiving general anesthesia during brain surgery.
  • Help find out if a person has a physical problem (problems in the brain, spinal cord, or nervous system) or a mental health problem.

How To Prepare

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

Do not eat or drink foods that have caffeine (such as coffee, tea, cola, and chocolate) for 12 hours before the test.

Since the electrodes are attached to your scalp, make sure your hair is clean and free of sprays, oils, creams, and lotions. Shampoo your hair and rinse with clear water the evening before or the morning of the test. Do not put any hair conditioner or oil on after shampooing.

To find certain types of abnormal electrical activity in the brain, you may have to be asleep during the recording. You may be asked not to sleep at all the night before the test or to sleep less (about 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.

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WebMD Medical Reference from Healthwise

Last Updated: October 10, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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