Patient Information

Electroencephalogram (EEG)


Neurophysiology is the study of brain, spinal cord nerve and muscle function. With our tests we record and interpret electrical signals from the body to help diagnose disorders.

What is an EEG?

An EEG (Electroencephalogram) is a simple test which records the electrical impulses from the brain. A standard EEG takes around 45 minutes to 1 hour and is recorded by video.

A sleep deprived EEG will take around 3 hours.

What do I need to do the day of my test?

  • Before you come for the test you can have your meals as normal and continue taking any medication that you are on unless you have been advised otherwise by your clinician.
  • Bring a list of your current medication and any allergies with you.
  • Ensure that your hair is clean and free from grease, hairspray, gel and any other hair care products including weaves.
  • You will be asked to sign a consent form for this test.

What will happen during the test?

  • This test is not painful.
  • The test will be carried out by an expert in electroencephalography, a clinical physiologist. You will be asked a few questions. If you have any questions about the test, please do not hesitate to ask. You can bring someone to your appointment if you wish.
  • The clinical physiologist will start by measuring your head and drawing some little dots with a marker on the surface of your head. The clinician will then gently rub the marks with some gel, before attaching 23 small discs to the surface of your head using a sticky paste. The paste can be easily removed with water.
  • You will then be asked to relax on a bed and to follow instructions such as opening and closing your eyes. You may also be asked to do a deep breathing exercise and to look at a flashing light during the test.

What do I need to know if I’ve been sent for a sleep EEG?

If you have been sent for a sleep deprived EEG, you should reduce your sleeping hours at least by half, for example: if you normally sleep for 8 hours you should aim for a maximum of 4 hours. Make sure you go to bed at your usual time. If you have epilepsy, there is always a small risk that you may have a seizure because of sleep deprivation and your doctor will discuss this with you.

For some sleep studies we may give you a sleep-promoting medication called Melatonin to help you go to sleep. You should not have any aftereffects other than drowsiness.

If you intend to drive to the appointment, you should be accompanied by a responsible adult as you will be too tired to drive safely and there is also the small possibility you might have a seizure if you are epileptic.

What happens after my test?

Once the test is complete the discs will be removed and you can return to your normal activities. There should be no side effects after the standard EEG (without sleep deprivation).

Small pieces of sticky paste may be left in your hair which easily washes out with shampoo and warm water.

If you come for a sleep deprived EEG you should be accompanied by a responsible adult as you will not be allowed to drive home after the test.

The results of the tests will take a few weeks to be analysed by the physiologist and consultant. You hospital clinician will contact you if something of concern is detected by the test, otherwise your hospital clinician or referring doctor will discuss the results with you at the next appointment.

Your GP will also receive a copy of the results and you can the GP for a copy, if you wish.

If you need further information about this or similar neurophysiological tests, please visit:

The British Society for Clinical Neurophysiology (bscn.org.uk)


Neurology (Neurophysiology Department) 020 8934 6156 (Option 3)

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