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What is an EEG?

EEG stands for Electroencephalogram, a recording of the electrical signals produced by the brain. In the media it is sometimes referred to as recording brainwaves.

The EEG gives information about the brain that is useful to your doctor in making a diagnosis in several different conditions. It is the only test that can produce this sort of information, but your doctor may also want to get information from other tests.


About our Department

West Surrey Clinical Neurophysiology is a specialist department, one of only a few in the country. We are based at St Peter’s Hospital in Chertsey but we provide our services to patients from several other hospitals too.

Please make sure you come to the right hospital!


Preparing for the EEG

Unless we ask you to change, please carry on taking all your usual medication as recommended by your doctor. Please bring a list of your medications with you.

You can eat as normal, including meals on the day of the test.

You should have a normal night’s sleep before the test.

We can only do the test if your hair is clean, dry and have easy access to your scalp. Please do not use any hair styling products. Please call us for advice if you have a wig, hair extensions, braids or weaves.


Arriving at St Peter’s Hospital

If you are unable to attend on the day of the test, please do let us know, using the contact details at the end of this webpage.

Our department is in the main outpatient block at St Peter’s Hospital. Please make your way to level two. Ours is the first clinical area on the right in the main outpatient corridor with green dots on the corridor walls. If you know St Peter’s, this area is just behind the W H Smith Shop and to the right of the Pharmacy. The signs say ‘EEG / EMG’ and ‘West Surrey Clinical Neurophysiology’.

The nearest car park is the main outpatient car park at the front of the hospital. Please note St. Peters Hospital operates payment parking systems. Further details are available online here.

It is helpful if you can arrive about 10 – 15 mins before the appointment time shown on the accompanying letter. We have only limited space in our waiting room, if you arrive earlier at the hospital you will be asked to wait elsewhere. There is a café at the main outpatient entrance nearby. We aim to keep to our appointment times, but if we are running late we shall let you know and we ask for your patience.


What happens during the EEG?

Your test will be carried out by a clinical physiologist, who will meet you in our waiting room and take you to the recording room. We shall explain the test to you and this is a good time to ask any questions you still have. The clinical physiologist will also ask you about your particular problem and about your health in general. He or she will also ask you to sign a consent form.

The clinical physiologist will measure your head and make marks with a skin pen. At each mark, he or she will rub the skin and then attach a small metal disc through which the recording is made. It is held in place with a sticky paste.

The investigation is painless and in most cases you will be lying down for the recording and will be asked to follow instructions, such as to close and open your eyes. No needles or electricity are used and we only record the signals which are produced naturally by your brain.

In most cases we use 'activation procedures' to improve the recording, including overbreathing and photic stimulation. The clinical physiologist will explain these to you and ask for your consent at the start of the test.


Sedation for Sleep EEG

In some cases it is useful to record the EEG whilst you sleep. We make this decision with the doctor who refers you. We shall give you tablets of a drug called melatonin to help you sleep. This is a naturally occurring drug that alters your body clock so that you sleep gently for a short period. It is unlike other sleeping tablets that “knock you out” and you should have no after effects. However if we need to do this part of the test you will need to be accompanied as you will not be allowed to drive home afterwards. If we need to do this part of the test it will say so on the appointment letter – your letter will say “Routine and Sleep EEG”. Otherwise the letter will just say “Routine EEG”.



The clinical physiologist will ask you to sign a consent form for the following two parts of the test.

Video recording - this is a useful tool in helping the medical consultant report on the EEG recording. The video is time locked to the recording, which means that the consultant can at any time play the video and see exactly what the patient is doing. This allows for a more detailed report which can be useful for some conditions.

Photic stimulation – this part of the test involves a flashing light, similar to a strobe light. This part of the test can be diagnostic for specific types of epilepsy. In a very small number of people there is a very slight risk of this triggering an event. If this happened there is a risk that you might lose your driving licence – you would have to discuss this with the doctor who referred you for the test. This is not the aim of the procedure and we take all possible steps to stop this happening.

We will discuss both of these areas further with you at the time of your appointment and the clinical physiologist will try to answer any questions you may have.


What happens after the recording?

After the recording the small discs will be painlessly removed and the paste dissolved by rubbing the area with clean warm water.

Your hair will still feel quite sticky afterwards.

There are no after effects from the EEG recording, which will take around one hour and you can leave immediately afterwards. A sleep EEG takes a little longer, about one and a half hours, but you can still go home afterwards.


What happens next?

Your EEG recording is reported at a later time by both the clinical physiologist, who gives a technical report which involves measuring all the different waveforms recorded, and the medical consultant who gives a clinical report. This report is sent to your hospital consultant. He or she will give you the result of the EEG test at a later date.

We also send a copy to your GP. We aim to prepare these reports in good time.


Contacting us

If you have any questions before your appointment please contact us and we will try our best to answer them. You can phone us on 01932 722543. We are open from 9am to 5 pm. There is also an answering machine outside these hours or if we are unable to take your call.

Our postal address is:

West Surrey Clinical Neurophysiology
St Peter’s Hospital, Guildford Road, Chertsey, KT16 0PZ


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