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    Electroencephalogram (EEG)

    How It Is Done

    An EEG may be done in a hospital or in a doctor's office. An EEG technologist does the test. The EEG record is read by a doctor who is trained to diagnose and treat problems that affect the nervous system (neurologist).

    You will be asked to lie on your back on a bed or table. Or you may sit in a chair with your eyes closed. The EEG technologist will attach several flat metal discs (electrodes) to different places on your head. A sticky paste is used to hold them in place. Instead of separate electrodes, you may wear a cap with several fixed electrodes. In rare cases, the electrodes may be attached to the scalp with tiny needles.

    The electrodes are hooked by wires to a computer that records the electrical activity in the brain. A machine can show the activity as a series of wavy lines on a piece of paper. Or the activity may be shown as an image on the computer screen.

    You will need to lie still with your eyes closed during the recording. The technologist will watch you directly or through a window during the test. The recording may be stopped from time to time. This allows you to stretch and change your position.

    The technologist may ask you to do different things during the test to see what activity your brain does at that time.

    • You may be asked to take deep and rapid breaths (hyperventilate). Usually you will take 20 breaths a minute for 3 minutes.
    • You may be asked to look at a bright, flashing light called a strobe.
    • You may be asked to go to sleep. If you can't fall asleep, you may get a sedative to help you sleep. If an EEG is being done to check a sleep problem, your brain's electrical activity may be recorded all night.

    An EEG takes 1 to 2 hours. After the test, you may do your normal activities. But if you had little or no sleep or were given a sleep medicine, have someone drive you home after the test.

    WebMD Medical Reference from Healthwise

    Last Updated: August 21, 2015
    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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