What is an EEG?

Your brain cells make electrical signals to send messages to each other and to your body. An electroencephalogram (EEG) is a test that measures the electrical activity of your brain. It's usually non-invasive, which means nothing goes inside your body.

Flat metal discs (called electrodes) are placed on your scalp (head) to pick up signals from your brain. The activity recorded is then shown on a computer as 'brain waves'.

If your brain's electrical activity is unusual, it will show up in the EEG recording. Even small changes can be seen. A specialist doctor looks at these brain waves to help diagnose different conditions.

When is an EEG used?

You may need an EEG to help diagnose or monitor conditions, such as:

• epilepsy and other types of seizures (fits)
• encephalopathy (brain function problems)
• encephalitis (brain inflammation)
• brain injuries
• brain tumours
• developmental conditions such as fetal alcohol spectrum disorder

While an EEG can diagnose epilepsy, a normal EEG result doesn't rule out epilepsy. This is because brain activity can return to normal between seizures.

An EEG can also be used to diagnose sleep disorders, such as:

• insomnia
• sleep apnoea
• narcolepsy (a brain condition that makes you very sleepy during the day and can cause you to suddenly fall asleep)

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Is an EEG safe?

An EEG is safe and has minimal risks.

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

Where can I get an EEG?

An EEG is usually done in a hospital, often in a specialist ward. You may need a referral to get an EEG.

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What happens during an EEG?

During an EEG a nurse or technician will set up the test:

• Discs are usually attached to a cap that is pulled over your head. The discs are coated in a special gel.
• Wires connect the discs to a computer.
• The computer records your brain waves.
• You will need to keep still during the test.
• You may be asked to do some deep breathing or look at a flashing light.

Sometimes, needle electrodes are used. If this is needed, you'll likely be asleep during the test.

If your child needs an EEG, you can bring items to help them feel calm, such as:

• something to watch on an electronic device
• their favourite blanket or stuffed animal
• stickers or small toys

Sometimes, unusual brain activity happens when we are tired or asleep. This is why some EEG tests are done while you are sleep-deprived (tired from not enough sleep). You may also be asked to sleep during the test.

An EEG usually takes about an hour, but it may take longer for a sleep recording.

What does an EEG feel like?

You shouldn't feel anything different during an EEG. If you are asked to look at flashing lights or breathe quickly, you may feel dizzy or lightheaded.

How do I prepare for an EEG?

Before your EEG, it's important 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. Don't use hair products such as:

• conditioners or hair oil
• hairsprays
• styling gels

Ask your doctor if you need to stop any medicines before the test.

If your doctor asks you to have a sleep-deprived EEG, you'll need to stay awake the night before your test without using caffeine or sugar. You shouldn't drive to your appointment.

Are there side effects or complications of an EEG?

Sometimes, an EEG can trigger a seizure if you or your child has a condition that causes seizures.

Talk to your doctor about any concerns you may have before having an EEG.

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Are there alternatives to an EEG?

Alternative tests that look at brain function include:

• magnetic resonance imaging (MRI) scan
• functional MRI scan
• computed tomography (CT) scan

Magnetoencephalography is similar to EEG, except that it measures the brain's magnetic activity. This can sometimes give more detailed images and information.

Resources and support

• The Medical Costs Finder helps you understand healthcare fees. Read more about paying for diagnostic tests.
• The Flinders Medical Centre has information on EEGs for children.
• The Children's Hospital Melbourne has information about EEGs and routine EEGs. They also offer a video guide to help children understand what to expect at the hospital.
• Sydney Neurology provides advice on how to prepare for an EEG.

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 you 24 hours a day, 7 days a week.