Why am I getting an EEG?

The EEG records your brainwaves and is used mainly to help diagnose epilepsy. It is the most common reason to be referred — to help work out whether episodes of collapse, fainting, blank staring or other sensations (a sudden wave of fear, déjà vu) might be related to epilepsy. An EEG can also help in looking after people with dementia, after head injury, and in other situations.

What happens during the EEG?

To prepare, please come in with clean, dry hair (no oils or products). A total of 23 small electrodes — gold-plated discs — are applied to your scalp with a sticky conductive paste, and your brainwaves are recorded for later analysis.

During the recording you will be asked to do a few simple things: open and close your eyes, breathe more rapidly (hyperventilate) for a short period, and close your eyes while a bright light flashes. These “activation” procedures can bring out different types of epilepsy, so they help make the diagnosis clearer — it is worth doing them as best you can.

Sometimes, to get more information, you will be asked to have a sleep-deprived EEG. This means going to bed and then waking very early — say 2am — and staying awake for the rest of the night (no coffee or other stimulants), so that you come in able to fall asleep for at least part of the recording. Sleep brings out epilepsy activity more readily. Because you will be tired, do not drive yourself to a sleep-deprived EEG.

A routine EEG takes about 40 minutes including putting on and removing the electrodes; a sleep-deprived EEG takes about an hour. Afterwards most people like to wash their hair, as a little paste is left behind.

What does an EEG show? When will I get my results?

The EEG can reveal several different abnormalities that, together with your symptoms, help diagnose the problem. Temporal-lobe and other epilepsies show changes such as spikes and spike-and-wave complexes.

The brainwaves themselves may show asymmetries — suggesting a possible structural problem in the brain — as well as changes from medication side effects, and patterns that can occasionally point to dementia or to brain dysfunction such as delirium.

Frequently asked questions

What does an EEG show?

An EEG records the brain’s electrical activity and can reveal patterns linked to epilepsy (such as spikes and spike-and-wave discharges), asymmetries that may point to a structural problem, and changes seen with some medications, delirium or dementia.

When will I get my EEG results?

Your EEG is reported the same day and sent to both your referring doctor and Dr Granot.

Is an EEG painful?

No. The electrodes simply sit on the surface of your scalp and only record — nothing is put into your head and there is no electric shock. The main inconvenience is a little paste left in your hair afterwards.

How do I prepare for an EEG?

Come in with clean, dry hair and no hair products. For a sleep-deprived EEG you will be asked to stay awake from very early in the morning (no coffee or stimulants) and not to drive yourself.

What is a sleep-deprived EEG?

An EEG performed after a deliberately short night’s sleep, which makes subtle epilepsy activity easier to detect. It lasts about an hour so there is time to fall asleep during the recording.

How long does an EEG take?

A routine EEG takes about 40 minutes including set-up; a sleep-deprived EEG takes about an hour.

Specialist resources from our network

For detailed information on specific clinical scenarios where an EEG is used:

• EEG for epilepsy
• EEG after a first seizure
• Sleep-deprived EEG
• EEG for fits, faints and blackouts
• EEG in dementia and cognitive decline
• EEG after head injury and concussion