Electroencephalogram (EEG): How It Is Done

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How It Is Done

An electroencephalogram (EEG) may be done in a hospital or in a doctor's office by an EEG technologist. The EEG record is read by a doctor who is specially trained to diagnose and treat disorders affecting the nervous system (neurologist).

You will be asked to lie on your back on a bed or table or relax in a chair with your eyes closed. The EEG technologist will attach 16 to 25 flat metal discs (electrodes) to different places on your head, using a sticky paste to hold the electrodes in place. A cap with fixed electrodes may be placed on your head instead of individual electrodes. In rare cases, these electrodes may be attached to the scalp with tiny needles.

The electrodes are hooked by wires to a computer that records the electrical activity inside the brain. A machine can show the activity as a series of wavy lines drawn by a row of pens on a moving piece of paper or as an image on the computer screen.

Lie still with your eyes closed during the recording, and do not talk to the technologist unless you need to. The technologist will watch you directly or through a window during the test. The recording may be stopped from time to time to allow you to stretch and reposition yourself.

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

You may be asked to breathe deeply and rapidly (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. This is called photic or stroboscopic stimulation.
You may be asked to go to sleep. If you cannot fall asleep, you may be given a sedative to help you fall asleep. If an EEG is being done to check a sleep problem, an all-night recording of your brain's electrical activity may be done.

An EEG takes 1 to 2 hours. After the test, you may do your normal activities. However, if you were sleep-deprived or given a sleep medicine, have someone drive you home after the test.

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Last updated:	September 01, 2006
Author:	Jan Nissl, RN, BS
Reviewed By:	Patrice Burgess, MD - Family Medicine, Barrie J. Hurwitz, MD - Neurology
Editors:	Susan Van Houten, RN, BSN, MBA, Tracy Landauer

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