Evoked responses

What are evoked responses?

Evoked responses are signals from the brain that are given out when it  receives a message from a flash (visual), a click (auditory) or a tingling sensation (sensory). That is, signals given out as a result of the things your child can see, hear and feel. There are 3 different types of evoked potential tests.

Please check your appointment letter to see which of the tests below your child is having.

We have experience in dealing with children of all ages and abilities. However, if you think it would help to bring in drinks, snacks and favourite toys then please feel free to do so.

What is the evoked response test?

The test records the signals to help study how well certain nerves in the body are working. It is a series of tests designed to look at the nerves controlling the:

1. Optic nerve that controls sight – the Visual Evoked Response (VER)
2. Auditory nerve that controls hearing – the Brainstem Auditory Evoked Response (BAER)
3. Sensory nerve that controls the nerves of the arms and legs – the Somatosensory Evoked Potentials (SSEP)

Where will the test be done?

The test is performed in a recording room on E Floor, Grey stairs or lifts, at Sheffield Children’s Hospital, S10 2TH.

The nearest entrance to the department is on Damer Street around the corner from the Emergency Department.

Then follow the signs to Grey lifts or stairs and travel to E floor and report to reception. You can also follow the signs for Grey lifts from the Main Entrance.

Public transport is the best way to travel to Sheffield Children’s Hospital. We are well served by bus services (51, 52, 273, 274, 275) and close to the tram route. Find out more on our public transport webpage: www.sheffieldchildrens.nhs.uk/patients-and-parents/public-transport

Q-Park Durham Road is opposite the new hospital wing. Please allow plenty of time for delays and roadworks. For up-to-date parking information visit the internet site. Please allow plenty of time for delays and roadworks. For up-to-date parking information visit our webpage on parking: www.sheffieldchildrens.nhs.uk/parking

Parents and carers should note, we are not able to allow other children to be supervised whilst your child is having their EEG. If you have any problems arranging childcare, please ring the department to discuss this.

How long will we be at the hospital?

Each of the tests takes about 1 hour. There will be a physiologist who does the test and there is room for parents or carers to come in.

How will these tests help my child?

You may wonder why they are having responses tested in a different area to the symptoms they are experiencing. For example, we may look at their leg when they have had a problem with their vision. This gives their consultant more information about how certain nerves are working and can help them to find the cause of their problem.

Is the test safe?

Yes. Occasionally patients experience minor skin irritations due to the products we use.

If your child is having a Somatosensory Evoked Potential (SSEP) and they have an implanted electronic device such as a vagal nerve stimulator or cardiac pacemaker, please tell the physiologist before they have the test done.

The Visual Evoked Responses test (VER)

Do we need to do anything before the test?

Yes, when coming for this test, you should make sure that:

• You bring your child’s glasses or contact lenses with you
• They have clean dry hair, free from any lacquer or gel products

What happens during the VER test?

The test looks at the response of the nerves and brain to light.

It takes about 1 hour to do and is painless. We will measure some points on their head and then small discs will be put on their head with sticky paste. They will have alternate eyes covered with a patch and then be asked to concentrate and watch a spot in the middle of a moving checkerboard pattern and a flashing light.

This will be repeated several times and the response can be measured. After the test the discs will be removed.  You may find a small amount of paste left in their hair which will wash out with shampoo.

The Brainstem Auditory Evoked Response test (BAER)

Do we need to do anything before the test?

Yes, when coming for this test, you should make sure that your child has clean dry hair, free from any hairspray or gel products.

What happens during the BAER test?

This test that looks at the responses of the nerves/brain to sound.

The test takes about 1 hour to do and is painless. We will measure some points on their head and then put small discs on your child’s head with sticky paste. They will then be asked to put some headphones on and they will hear a clicking noise.

They will hear the clicks in each ear separately. The test will be repeated a few times and the response can be measured.

After the test, the discs will be removed and their hair will be cleaned.  You may feel a small amount of the sticky paste left in their hair which will wash out with shampoo.

The Somato-Sensory Evoked Response test (SSER)

Do we need to do anything before the test?

Yes, when coming for this test, you should make sure that your child:

• Has clean dry hair, free from any lacquer or gel products
• Is wearing appropriate loose clothing. We will need to reach their arms, shoulders and neck if the arm is being tested.  We need to reach their ankles and the back of their knees if the leg is being tested.

If your child is having a Somatosensory Evoked Response test and they have a cardiac pacemaker, please tell the physiologist before they have the test done.

What happens during the SSER test?

This test looks at the response of the brain to a tingling sensation given to their arm or leg. The tests take about 45 minutes to do. 

During the test, we will measure some points on their head and then put small discs on their head with sticky paste. If they are having an arm tested, they will also have a pad attached to the wrist and stickers on their shoulders and neck. If the leg is tested they will have a pad on their ankle and stickers at the back of their knee. A message is passed through the pad at the wrist or ankle. They will feel a tapping or tingling sensation.

This may result in a small twitch in the muscle in the hand or foot. Left and right sides will be tested separately and the test will be repeated several times. After the test, the discs will be removed.  You may find a small amount of paste left in their hair which will wash out with shampoo.

When will we get the results?

You will not get the results of these tests on the same day because it takes time to analyse them. The report will be sent to the referring consultant within 2 to 5 working days and they will then discuss the results with you.