Overview

An electroencephalogram (EEG) is a test to record the electrical activity in the brain. Recording this activity can give us useful information about how your brain is working. This helps to diagnose conditions that affect the brain. There is no other way that we can get this information.

‘Day case’ means that the procedure will be done during the day and you will not need to stay in hospital overnight.

A physiologist will monitor your EEG for a maximum of 7 hours, in the EEG department. The test might be shorter than this. You will be filmed throughout the test. We can record any movements or episodes which happen during the EEG.

An EEG is not a scan of the brain, and it’s not a painful procedure.

Why you need this test

You may have a day case EEG if you have already had a shorter EEG test, lasting 1 to 2 hours. This is because sometimes abnormal brain activity or episodes are not recorded during the shorter test. 

A longer recording increases the chances of us recording abnormal brain activity or an episode. This can help us understand how many episodes you have over a period of time.

Giving your permission (consent)

We want to involve you in decisions about your care and treatment. If you decide to have the procedure or treatment, we will ask you to sign a consent form. This says that you understand what is involved and agree to have the treatment.

Read more about our consent process.

Preparing for an EEG

On the day of the EEG

The test is done by a physiologist.  

1. Your physiologist will mark areas on your scalp with a soft crayon. 
2. They will rub gel into the marked areas, and stick small silver discs (electrodes) to your scalp with a sticky paste (similar to petroleum jelly). 
3. They will place tape over each electrode to hold it in place. 
4. Some netting will be placed over the wire to stop the electrodes moving throughout the day. 

The electrodes are connected to a small box, known as a headbox, which records the EEG trace. This box can be placed into a small bag, so that you can move around and go to the toilet. You will usually be asked to move to a bed, and be made comfortable. The recording will then start. 

During the test

You might be asked to do 3 things during the EEG recording. Your physiologist will fully explain each part of the test on the day. 

Part 1 – Relaxation 

You will be asked to close your eyes and relax. If you feel drowsy during this time, it is OK to fall asleep. The test may then go on for longer to record your brain waves while you sleep. 

Part 2 – Deep breathing 

Depending on your medical history, you might be asked to do some deep breathing. This exercise might produce short-term changes in the electrical activity of your brain, which can help in your diagnosis. 

The physiologist will show you how to breathe during this time. You might feel dizzy or feel tingling in your hands, feet, or lips when doing this exercise. This is common and will pass when your breathing returns to normal.

Part 3 – Flashing lights 

The physiologist will ask you to look at a light which will flash at different speeds, for short periods of time. This exercise can help in your diagnosis, particularly if you have seizures or blackouts caused by flashing lights.

Risks of a day case EEG

There are no known side effects of an EEG. There is a very small risk that parts 2 and 3 of the test could cause a seizure or blackout. If this happens, the exercise will be stopped immediately and you will be looked after in the department until you are well enough to go home. 

After the EEG

1. The electrodes will be removed from your scalp. 
2. Your hair may be cleaned to remove the sticky paste. If it isn’t all removed, you can wash it out with shampoo. 
3. If you have had a sleep-deprived test, you may need someone to escort you when you leave hospital. 

There are no known side effects for an EEG, so you can continue any normal activity after the test. 

The physiologist and neurophysiologist will look at the results of your test. They will then send a full report to the doctor that referred you. 

Your referring doctor will share the results of the test with you. They won’t be available on the day of your test. 

Follow-up appointment

The doctor who referred you should book a follow-up appointment with you. If this has not been done, you will need to contact them to arrange this.