An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain. Special sensors called electrodes are attached to your head. They're hooked by wires to a computer. The computer records your brain's electrical activity on the screen. Or it may record the activity on paper as wavy lines. Changes from the normal pattern of electrical activity can show certain conditions, such as seizures.
Why It Is Done
An EEG may be done to:
- Check for epilepsy and see what type of seizures are occurring. EEG is the most useful and important test for checking if someone has epilepsy.
- Check for problems with loss of consciousness or dementia.
- Help find out a person's chance of getting better after a change in consciousness.
- Find out if a person who is in a coma is brain-dead.
- Study sleep disorders, such as narcolepsy.
- Watch brain activity while a person is getting general anesthesia for brain surgery.
- Help find out if a person has a physical problem or a mental health problem. Physical problems include problems in the brain, spinal cord, or nervous system.
How To Prepare
Before the day of the EEG test, tell your doctor if you are taking any medicines. Your doctor may ask you to stop taking certain medicines before the test. They include sedatives and tranquilizers, muscle relaxants, sleeping aids, and medicines used to treat seizures. These medicines can affect your brain's usual electrical activity. Taking them may affect your test results.
Do not eat or drink things that have caffeine for 12 hours before the test. This includes coffee, tea, cola, and chocolate.
The electrodes will be attached to your scalp. Make sure that your hair is clean before the test. Don't put sprays, oils, creams, or lotions in your hair. Shampoo your hair and rinse with clear water the night before or the morning of the test. Do not put any hair conditioner or oil in your hair after you wash it.
To find certain types of abnormal electrical activity in the brain, you may have to be asleep during the test. You may be asked not to sleep at all the night before the test. Or you may need to sleep less (about 4 or 5 hours) by going to bed late and getting up early. If your child is going to be tested, try to keep him or her from taking naps just before the test. If you know that you are going to have an EEG with little or no sleep, plan to have someone drive you to and from the test.