How It Is Done continued...
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 several 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
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
- 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 can't 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. But if you were sleep-deprived or given a sleep medicine,
have someone drive you home after the test.
How It Feels
There is no pain with an
If paste is used to hold the
electrodes, some paste may stay in your hair after the test, so you will have
to wash your hair to remove it. If needle electrodes are used (which is rare),
you will feel a brief, sharp prick (about like having a hair pulled out) when
each electrode is inserted. If electrodes are placed in your nose, they may
cause a tickling feeling and, rarely, some soreness or a small amount of
bleeding for 1 to 2 days after the test.
If you are asked to
breathe rapidly, you may feel lightheaded or have some numbness in your
fingers. This reaction is normal. It will go away a few minutes after you start
breathing normally again.