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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 a Prolonged EEG Recording

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, unless instructed otherwise.

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 bottom 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?

This hospital performs two types of Prolonged EEG Recording:

  • Multiple Sleep Latency Test (MSLT)
  • Ambulatory EEG Recording (24/48 hours)

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.

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 attach a small metal disc through which the recording is made. It is held in place with a sticky paste.


Multiple Sleep Latency Test

In some very specific cases a number of EEG recordings are required over a 7-8 hour period.

With the 1st recording starting at 9 am followed by further recordings at around 11 am; 1 pm; 3 pm and on very rare occasions 5 pm.

You are able to leave the department and visit the coffee shop for lunch or a snack in between the recordings if you wish or sit in the waiting area reading.

For this test you will be sent a sleep hygiene diary for the week prior to your appointment. It is important that this is filled in as a best you can as this information will have some bearing on the test results.

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.

We often record a normal EEG too during one of the recordings. 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.



The clinical physiologist will ask you to sign a consent form for the following two areas 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 diagnostic 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 useful 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 MSLT 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 sticky afterwards.

There are no after effects from the EEG recording and you can leave immediately after the last recording.


Ambulatory EEG with video

This is a prolonged EEG for 24 or 48 hours, looking at a very specific diagnostic question and the majority of people will have had some type of EEG recording before.

You will be given 2 appointments, 1 for setting the test up and the 2nd for removal of the discs.

For this test the small discs will be attached to the head with strong adhesive (glue), which will keep the discs in place for the required time. The discs are then attached to a small portable device which is usually worn around the waist and you are then free to go home and go about your daily life.

You will also be given a portable video camera as part of this recording.

You will be asked to keep a diary sheet during this recording and return it to the department.

You will be unable to bathe, shower or wash your hair whilst attached to this recording device.

We suggest that you wear a button up shirt or top as you will be unable to lift any clothing up over your head whilst attached to the recording device. You may also wish to bring a hat or cap to cover your head.



The clinical physiologist will ask you to sign a consent form for the following part 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.


What happens after Ambulatory EEG recording?

After the recording is stopped and the information downloaded and checked to ensure the full recording time has been obtained the small discs will be removed from the head. We will use a purpose-made remover for this which does have a fairly strong smell.

Your hair will need a thorough wash and we will give advice as to how to remove any residual adhesive.

You can leave immediately after this.


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 and he or she will give you the result of the EEG test at a later date.

A copy may be sent 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 9 am to 5 pm. There is 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
KT16 0PZ


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