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What happens during the test?

This part of the test takes about 1 to 1½ hours.

You will not feel anything whilst the EEG is being recorded.

Please note, we routinely video the test in case you have any symptoms that we might need to re-examine. Video clips of any symptoms are kept as part of your records. All remaining video is deleted after the doctor has completed the report. We will ask for your consent to do this. We may also ask for your permission to use the video for teaching purposes, you will be asked to give consent separately for this purpose.

During the test we will want you to be as comfortable as possible. Most people find that they are comfortable lying down on a couch.

You may go to sleep naturally for a short period whilst you are in the department.

During the test, the technician will ask you to do various simple actions like:

•      Opening and closing your eyes.

•      Hyperventilation - this is taking deep breaths in and forcing them out as if you are blowing a candle out.

You may feel dizzy or get pins and needles in your fingers, toes and face. These are normal side effects which will go a few minutes after you have stopped the deep breathing. We will ask about your general health (heart, asthma, etc) to make sure it is safe for you to do the deep breathing. The breathing causes a change in the blood flow which may change your brain waves and provide extra information to help with your diagnosis. If you are being investigated for seizures, there is a less than 3 in 100 risk that the deep breathing may cause a seizure. If that happens it could mean you are unable to drive for 1 year afterwards. You will be asked to give your consent to performing this; there are no alternatives to this part of the test.

•      Photic stimulation - watching a flashing light. A lamp is placed in front of you which flashes on and off at different speeds. You will be asked to look at it. In a small percentage of patients, flashing lights trigger seizures (photosensitivity). If a patient has this response the light is turned off quickly and they do not usually go on to have a seizure. However there is a less than 1 in 10,000 risk that if you are having seizures, a seizure could be triggered by the flashing light. If that happens it could mean you are unable to drive for 1 year afterwards. The information we get from photic stimulation may lead to a definite diagnosis and help your consultant to decide on your treatment. You will be asked to give your consent to performing this; there is no alternative way to get this information.

•      You will be left undisturbed for a while. Sleep deprivation is said to slightly increase the risk of a seizure. There are no definite figures available because of different methods in use but the risk

is small and falls between the risks quoted above for hyperventilation and photic stimulation.

What happens after the test?

Once the test is finished, we remove the discs from your head. You may find a small amount of paste left in your hair and this is easily washed out with shampoo. You may wish to bring a hat or cap to wear.

When will I get the results?

You will not get the results on the day of your test because it takes time to analyse them. The report will be posted to your referring consultant within 2-5 days.

Your consultant will then contactyou to discuss the results.

Some frequently asked questions

Are any needles involved?

No

Can you read my mind?

No, we can only pick up the electrical activity in your brain not any thoughts you have.

What if I want more information?

If you have any questions after reading this leaflet please ring the Department of Clinical Neurophysiology, Royal Hallamshire Hospital on:

• 0114 271 3237

Monday - Friday 8:30am-4:30pm