What is an EEG test?

Your brain cells produce electric signals to communicate with each other and the rest of your body. An electroencephalogram, or EEG, is a test that measures the electrical activity of your brain.

This electrical activity is recorded by placing flat metal discs (electrodes) on your scalp. The activity recorded is then shown on a computer as ‘brain waves’.

If something is unusual about your brain’s electrical activity, it will show up in the EEG recording. A specialist doctor can look at these brain waves to help diagnose different conditions.

Sometimes, unusual brain activity happens when we are tired or asleep. Because of this, some EEG tests are done while you are sleep deprived.

When is an EEG used?

Your doctor may recommend an EEG to help diagnose or monitor conditions such as:

• epilepsy and other types of seizures (fits)
• encephalopathy (brain dysfunction that may have a variety of causes)
• encephalitis (brain inflammation)
• developmental disability, such as fetal alcohol spectrum disorder

It can also be used to diagnose different sleep disorders, such as:

• insomnia
• sleep apnoea

While an EEG can diagnose epilepsy, a normal EEG test does not rule out epilepsy. This is because brain activity can return to normal between seizures.

How do I prepare for an EEG test?

When having an EEG, it’s best that your hair is clean and dry. Wash your hair the day before your test. This will help the discs stay attached to your scalp. Avoid using hair products such as:

• conditioners or hair oil
• hairsprays
• styling gels

Your doctor will let you know if you need to stop taking any of your medicines before the test.

Your doctor may ask you to do a sleep deprived EEG. If so, you will need to stay awake the night before your test without the help of caffeine or sugar. If you are having a sleep deprived EEG, you should not drive to your appointment.

What happens during an EEG?

An EEG is usually done in a hospital, on an EEG ward. During the EEG, discs will be placed all over your scalp (head). They are usually kept in place with a sticky paste that can be easily washed out of your hair.

The discs will be attached to wires which send electrical signals to a computer. The computer will record your brain waves. You won’t feel any sensations from the discs. You will need to keep still during the test.

If your child needs an EEG, you can bring things to keep them distracted and relaxed, such as:

• something to watch
• their favourite blanket

During an EEG, you may be asked to do some deep breathing or look at a flashing light. If you have had a sleep-deprived EEG, you may be asked to sleep during the test.

An EEG usually takes about an hour but may be longer for a sleep recording.

What are the possible risks of an EEG?

An EEG is a safe, non-invasive test that does not hurt.

The discs used during an EEG only record electric signals, they do not produce them. This means there is no risk of electric shock.

Sometimes, an EEG can cause a seizure if you or your child has a condition that causes seizures. You can talk to your doctor about any concerns you may have before having an EEG.

Resources and support

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with 24 hours a day, 7 days a week.