What Is an EEG (Electroencephalogram)?

An EEG, or electroencephalogram, is a test that records the electrical signals of the brain. Doctors use it to help diagnose epilepsy and sleep disorders.


Let your doctor know about any medications -- both prescription and over-the-counter -- and supplements you're taking.

Wash your hair the night before the test. Don't use any leave-in conditioning or styling products afterward. If you are wearing extensions that use glue, they should be removed.


You lie down on the exam table or bed, and a technician puts about 20 small sensors on your scalp. These sensors, called electrodes, pick up electrical activity from cells inside your brain called neurons and send them to a machine, where they show up as a series of lines recorded on moving paper or displayed on a computer screen.

You'll relax with your eyes open first, then with them closed. The technician may ask you to breathe deeply and rapidly or to stare at a flashing light, because both of these can change your brain wave patterns. The machine is only recording the activity of the brain and does not stimulate it.

It's rare to have a seizure during the test.

You can have an EEG at night while you're asleep. If other body functions, such as your breathing and pulse, are also being recorded, the test is called polysomnography (PSG). In some cases, you may be sent home with an EEG device which will either send the data directly back to your doctor's office, or record it for later analysis.


The technician will take the electrodes off and wash off the glue that held them in place. You can use a little fingernail polish remover at home to get rid of any leftover stickiness.

Unless you're actively having seizures or your doctor says you shouldn't, you can drive home. But if the EEG was done overnight, it's better to have someone else drive you.

You can usually start taking medications you'd stopped specifically for the test.

A neurologist, a doctor who specializes in the brain, will look at the recording of your brain wave pattern.

WebMD Medical Reference Reviewed by Christopher Melinosky on July 20, 2019



Epilepsy Foundation.

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