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Definition
The electroencephalogram (EEG) is a test. It is used to look at the electrical activity in the brain.
Reasons for Test
An EEG may be done to:
- Help diagnose seizures
-
Assess if brain function has been affected by certain conditions and diseases, such as:
- Trauma
- Coma
- Brain infection (encephalitis)
What to Expect
Prior to Test
Depending on the reason for your EEG, you may be given some of the following instructions:
- Ask your doctor whether to stop any medicines, such as stimulants, prior to the test.
- Avoid caffeine for eight hours before the test.
- Shampoo your hair the day of the test. Do not use hairspray or gel that day.
- If you are having a sleep-deprived EEG, you may need to stay awake the night before the test. You should also arrange for a ride to and from the test.
- If you are prone to seizures, arrange for a ride to and from the test.
Description of Test
You will sit in a chair or lie on a cot. Electrodes will be placed on your scalp with special gel or paste. The electrodes will record the brain's electrical activity. You will be asked to close your eyes and be still for most of the test. Depending on the reason for the test, there may be other steps such as:
- You may be asked to breathe deeply and rapidly.
- The technician may turn on a strobe light that sends fast pulses of light.
In some cases, the doctor will make a video recording of the test.
After Test
The technician will remove the electrodes, and you will be able to go home.
Talk to your doctor about restarting any medicines you may have stopped.
How Long Will It Take?
The test may take about one hour. In some cases, an EEG is done overnight or over a number of days. The test may be done at home or in the hospital.
Will It Hurt?
No, an EEG is painless.
Results
A specialist will review your test results. Your doctor will get a report within 1-2 weeks of your test and talk to you about the results.
Call Your Doctor
Call your doctor if you have a seizure disorder and you have a change in your regular seizure pattern once you have restarted your anti-seizure medicine.
Last reviewed September 2012 by Rimas Lukas, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
