What is it?
Electroencephalogram (EEG) is a test that detects electrical activity in your brain using small metal discs (electrodes) attached to your scalp. Your brain cells communicate via electrical impulses and are active all the time, even when you're asleep. This activity shows up as wavy lines on an EEG recording.
Why it is done?
EEG is one of the main diagnostic tests for epilepsy. EEG may also play a role in diagnosing other brain disorders.
An EEG can determine changes in brain activity that may be useful in diagnosing brain disorders and epilepsy. An EEG may be helpful for diagnosing or treating the following disorders:
- Epilepsy or other seizure disorder
- Brain tumor
- Head injury
- Brain dysfunction that may have a variety of causes (encephalopathy)
- Inflammation of the brain (encephalitis)
- Sleep disorders
An EEG may also be used to confirm brain death in someone in a persistent coma. A continuous EEG is used to help find the right level of anesthesia for someone in a medically induced coma.
How to prepare?
To prepare for an EEG:
- You should arrive 15 minutes before your appointment time to complete all necessary paper work
- Wash your hair the night before or the day of the test, but don't use any conditioners, hair creams, sprays or styling gels. Hair products can make it harder for the sticky patches that hold the electrodes to adhere to your scalp.
- Continue normal diet. Attempt to eat a meal within two hours of your scheduled test.
- Avoid anything with caffeine on the day of the test, because caffeine can affect the test results.
- Take your usual medications unless instructed otherwise.
If you're supposed to sleep during your EEG test, your doctor may ask you to sleep less or even avoid sleep entirely the night before your EEG.
How it is done:
You will be asked to lie on your back on a bed or table or relax in a chair with your eyes closed. Neurotechnologist will attach several metal discs (electrodes) to different places on your head, using a sticky paste to hold the electrodes in place.
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 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 can't fall asleep, you may be given a sedative to help you fall asleep.
How long will it take?
An EEG takes 45 minutes to 1.30 hours. After the test, you may do your normal activities.
How it feels?
There is no pain with an electroencephalogram (EEG).
Sticky 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 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.
After the test?
After the test, the technician removes the electrodes or cap. If no sedative was given, you should feel no side effects after the procedure, and you can return to your normal routine.