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Quick Facts

Electroencephalography (EEG)


The Manual's Editorial Staff

Last full review/revision Sep 2020| Content last modified Sep 2020
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Brain waves are electrical signals your brain makes. Your brain is always making electrical signals, even when you're asleep. Certain brain problems such as seizures cause changes in your brain waves.

What is an EEG?

EEG is a simple, painless test that records your brain’s electrical activity to see how well different areas of your brain are working. Doctors use EEG to check problems such as seizures. Doctors will place small sticky sensors on your scalp that detect your brain waves and send them to a recording device.

When you get an EEG, doctors may test your senses, such as hearing, seeing, or feeling, to see how well your brain responds. For example, they may shine a light in your eyes to see activity in your brain’s vision area.


An EEG is a recording of your brain's electrical activity. The test is simple and painless. About 20 small sticky electrodes are placed on your scalp and your brain activity is recorded.


Why would I need an EEG?

Your doctor may order an EEG to look for:

What happens during an EEG?

For an EEG:

  • Follow your doctor's instructions to prepare—you may be told to wash your hair the night before and not use hair products after rinsing

  • For the test, doctors put about 20 small sensors on your scalp—they are sticky, so they cling to your skin

  • The sensors are connected with wires to a machine, which records wavy lines to show your brain wave patterns

The printout (record) of your brain's electrical changes is the EEG. Doctors will look at it to see if there are abnormal patterns.

What are the problems with an EEG?

The test is painless and doesn't cause any problems afterward.

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