Health Information and Tools > Patient Care Handouts >  Electroencephalogram (EEG): About This Test
Facebook Tweet Email Share

Main Content

Electroencephalogram (EEG): About This Test

Woman having an EEG

What is it?

An electroencephalogram (EEG) lets a doctor see the electrical activity of your brain.

You will have small pads or patches attached to different places on your head. These are called electrodes. Wires connect the electrodes to a computer.

The computer records the activity of the brain. This looks like wavy lines on the computer screen or on paper.

Why is this test done?

The test is often used to diagnose epilepsy. It helps a doctor know what types of seizures are happening.

An EEG can also check brain activity in people with sleep disorders.

It can also help a doctor know why a person passed out (lost consciousness).

How can you prepare for the test?

  • Tell your doctor if you are taking any medicines. Your doctor may ask you to stop taking certain medicines before the test. These include sedatives and tranquilizers, muscle relaxants, sleeping aids and seizure medicines.
  • Do not eat or drink anything with caffeine in it for 12 hours before the test. This includes cola, energy drinks, and chocolate.
  • Shampoo your hair and rinse with clear water the evening before or the morning of the test. Do not put any hair conditioner or oil on after you wash your hair.
  • Your doctor may ask you not to sleep the night before the test or to sleep for only about 4 or 5 hours. This is because some types of brain activity can only be seen if you are asleep. If your doctor asks you to get less sleep than normal, plan to have someone drive you to and from the test.

What happens during the test?

  • You will lie on your back on a bed or table. Or you might relax in a chair with your eyes closed.
  • A technologist will attach the electrodes to different places on your head. Or you might get a cap with fixed electrodes on it.
  • You will lie still with your eyes closed. The technologist will tell you not to talk unless you need to.
  • The technologist may ask you to:
    • Breathe deeply and rapidly. This is called hyperventilating.
    • Look at a bright, flashing light called a strobe.
    • Go to sleep. If you can't fall asleep, you may get medicine to help you.

What else should you know about the test?

  • There is no pain. No electrical current goes through your body.
  • If you have a seizure disorder such as epilepsy, the flashing lights or hyperventilation may cause a seizure. The technologist is trained to take care of you if this happens.
  • If electrodes are put in your nose, they may tickle. In rare cases, they can also cause some soreness or a small amount of bleeding for 1 to 2 days after the test.

How long does the test take?

  • The test will take about 1 to 2 hours.

What happens after the test?

  • You will probably be able to go home right away. But if you didn't sleep your normal amount before the test, have someone drive you home.
  • You can go back to your usual activities right away.

When should you call for help?

Watch closely for changes in your health, and be sure to contact your doctor or nurse call line if:

  • You have any problems that you think may be from the test.
  • You have any questions about the test or have not received your results.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

Go to

Enter F196 in the search box to learn more about "Electroencephalogram (EEG): About This Test".

Care instructions adapted under license by your healthcare professional. If you have questions about a medical condition or this instruction, always ask your healthcare professional. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.