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Electroencephalogram (EEG) is a test to measure the electrical activity of the brain.
How the Test is Performed?
Brain cells 'talk' to each other by producing tiny electrical signals, called impulses. An EEG helps measure this activity. The test is
done by a EEG specialist in your doctor's office or at a hospital or laboratory.
You will be asked to lie on your back on a bed or in a reclining chair.
Flat metal disks called electrodes are placed all over your scalp. The disks are held in place with a sticky paste. The electrodes
are connected by wires to a speaker and recording machine.
The recording machine changes the electrical signals into patterns that can be seen on a computer. It looks like a bunch of wavy
You will need to lie still during the test with your eyes closed because movement can change the results. But, you may be asked
to do certain things during the test, such as breathe fast and deeply for several minutes or look at a bright flashing light.
How to Prepare for the Test?
Wash your hair the night before the test. Do not use any oils, sprays, or conditioner on your hair before this test. If you have a
hair weave, you may want to ask your doctor or nurse for special instructions.
Your health care provider may want you to stop taking certain medications before the test. Do not change or stop taking
medications without first talking to your health care provider. Bring a list of your medications with you.
Avoid all food and drinks containing caffeine for 8 hours before the test.
Sometimes you may need to sleep during the test, so you may be asked to reduce your sleep time the night before. If you are
asked to sleep as little as possible before the test, do not eat or drink any caffeine, energy drinks, or other products that help
you stay awake.
Routine EEGs are done in the office. Your doctor may also set you up for an ambulatory EEG wherein you are sent home for a
period of time with electrodes connected. Make sure you do not wash your hair or pull out the electrodes. You may cover your
head with a shower cap.
How the Test Will Feel?
The electrodes may feel sticky and strange on your scalp but should not cause any other discomfort. You should not feel any
discomfort during the test.
Why the Test is Performed?
EEG is used to look at your brain activity. It can help diagnose seizures. It may also be used to diagnose or monitor the following
Abnormal changes in body chemistry that affect the brain
Brain diseases such as Alzheimer's disease
Additionally, EEG is used to:
Evaluate problems with sleep ( sleep disorders)
Investigate periods of unconsciousness
Monitor the brain during brain surgery
Brain electrical activity has a certain number of waves per second (frequencies) that are normal for different levels of alertness.
For example, brain waves are faster when you are awake, and slower when you are sleeping.
What Abnormal Results Mean?
Abnormal results on an EEG test may be due to:
Abnormal bleeding (hemorrhage)
An abnormal structure in the brain (such as a brain tumor)
Tissue death due to a blockage in blood flow (cerebral infarction)
Drug or alcohol abuse
Migraines (in some cases)
Seizure disorder (such as epilepsy or convulsions)
Sleep disorder (such as narcolepsy)
Swelling of the brain (encephalitis)
Note: A normal EEG does not mean that a seizure did not occur.
The procedure is very safe. However, the flashing lights or fast breathing (hyperventilation) required during the test may trigger
seizures in those with seizure disorders. The health care provider performing the EEG is trained to take care of you if this
It may be difficult to get the paste out of your hair, but it should come out after a few washings with regular shampoo.
REFERENCE: http://www.nlm.nih.gov/medlineplus/ency/article/003931.htm A service of the U.S. National Library of Medicine
National Institutes of Health
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