What is an EEG?

EEG is the short way of saying electroencephalogram.  In your brain there are electrical signals being passed around. These signals are called brain waves. The EEG machine measures your brain waves and records them on the computer.  The picture looks like wavy lines on the computer screen. No matter what you are doing, whether you are running, reading or sleeping, your brain always has brain waves. The EEG measures these brain waves and shows where they are in your brain and how big the waves are.

Why do I need to have an EEG?

The most common reason people have an EEG is when someone has a seizure or epilepsy, although there may be other reasons. If you are having an EEG, the doctor wants to know what is happening in your brain, and an EEG can help. The EEG measures the brain waves in your brain; it helps the doctor to see how your brain is working and where in the brain the problem is.   This helps the doctor decide what is the best medicine or treatment for you.

What does an EEG machine look like?

An EEG is a computer that has lots of wires attached to it. The wires have a sticky end that attaches to your head.  There is a bed that is beside the EEG computer, this is where you will lie down.

What happens when I have an EEG?

A porter will come and bring you to the area where you will have the EEG. A technologist (the person who does the test) will greet you and explain what will happen.  You may be given a gown to wear, this looks like a backward housecoat, or you may already be wearing one.

The technologist will ask you to lie down on a bed. She will then take the wires that are attached to the machine and place them on your head. The technologist will use a sticky soft tape and gel to help the wires stay in place. These wires are called electrodes; they measure your brain waves.

It is important to lie very still on the bed while the test is happening. Sometimes they will ask you to try to fall asleep so that they can see what your brain does when you are resting. They may also ask you to rest with your eyes open or closed, take breaths really fast or look at a flashing light. The test can take about 45 minutes. When the test is done, the technologist will remove the wires from your head and wipe off the sticky gel.

What will the EEG test feel like?

An electroencephalogram does not hurt. The gel might feel a little cold. The tape is a special gentle tape that is less sticky than a regular Band-Aid.  While the test is going on you will be able to see your brain waves on the computer screen.

Preparing for the test

Your nurse will give you the information you need to help you get ready to have your EEG.


If you have any questions about the test, always ask!

This content has been reviewed and approved by health care team members at McMaster Children’s Hospital in Hamilton, Ontario. All content is for educational purposes only. For further information, please speak with your health care team.

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