Electroencephalogram (EEG)

What is an EEG?

An EEG (electroencephalogram) is a test that records the electrical activity in your brain. Your brain cells communicate using tiny electrical signals, sometimes called brainwaves, and an EEG picks these up through electrodes placed on your scalp.

Why might I need an EEG?

You might have an EEG to help diagnose or monitor a brain condition. The main reason is epilepsy, and you may be referred for one if you have symptoms such as seizures, blackouts, confusion, fainting or memory loss.

It can also be used for sleep conditions, encephalitis (inflammation of the brain), and to help monitor conditions such as brain tumours or the after-effects of a traumatic brain injury.

What are the benefits of having one?

An EEG is a safe way to check how your brain is working without the need for sedation or an anaesthetic. It can help your doctor reach a diagnosis and decide on the right treatment, and can be used on almost anyone, whatever their age or ability.

Are there different types of EEG?

There are several types, and which one you have depends on what your doctor needs to find out:

• A routine EEG: This is the standard type, usually lasting under an hour
• A sleep EEG: This is done while you're asleep in hospital
• A sleep-deprived EEG: This is done after you've been asked not to sleep for a set amount of time the night before, so you'll need to arrange for someone to collect you afterwards, as you won't be able to drive
• An ambulatory EEG: This is where you wear a portable recording machine for a day or more while going about your normal activities
• A video telemetry EEG: This is where a video recording is taken alongside the EEG, usually over a few days in hospital.

How do I prepare for an EEG?

Make sure your hair is clean, dry, and free from products such as gel, wax, mousse or hairspray, and remove any wigs, weaves or braids beforehand if you wear them. Bring a hairbrush or comb to tidy your hair afterwards.

You can usually eat and drink as normal, and continue taking your medicines as usual unless told otherwise, though you should tell your doctor about anything you're taking.

For a sleep-deprived EEG, you'll be asked to stay awake for a set time the night before. You can also ask for a chaperone to be with you during the test.

What happens during the test?

A routine EEG usually follows these steps:

1. You'll sit in a chair or lie on a bed
2. A healthcare professional measures your head and marks where the electrodes will go
3. Small metal or silver discs (electrodes) are attached to your scalp using a sticky paste or glue, which doesn't hurt
4. The electrodes are connected by wires to a recording machine, which tracks your brain's electrical activity on a screen
5. You may be asked to do certain things during the recording, such as opening and closing your eyes, breathing deeply for a few minutes, or looking at a flashing light.

The test is painless and usually takes around 20 minutes to an hour, depending on the type you're having.

What happens after the test?

The electrodes are removed and your scalp is cleaned, though your hair may still feel a little sticky until you wash it yourself. You'll usually be able to go home and carry on with your normal activities straight after the test.

It may take a few days or weeks for a specialist to analyse your results. You'll usually be given a follow-up appointment to discuss them, and if you haven't heard anything after a few weeks, contact the doctor who referred you.

What are the risks?

An EEG itself is painless and has no lasting after-effects. Some people feel a little dizzy during the deep breathing part of the test, and you may notice minor, temporary hair loss or skin irritation where the electrodes were placed.

In rare cases, if you have certain types of epilepsy, the deep breathing or flashing lights used during the test could trigger a seizure. Your healthcare professional is trained to help if this happens and will stop these parts of the test if necessary.