This leaflet answers common questions about evoked potential tests. If you would like further information, or have any particular worries, please do not hesitate to ask the physiologist performing your test.

A physiologist will explain the test to you on the day of your appointment and answer any questions you may have.

What are evoked potentials?

Evoked potentials are a recording of electrical signals produced naturally in the brain. Depending on the test requested by your doctor, this test can be used to record your brain’s response to light (visual evoked potentials), feeling in the hands and feet (somatosensory evoked potentials) or sound (brainstem auditory evoked potentials).  

These tests are sometimes requested if you have noticed any changes to your vision, sense of touch or hearing to help us understand if the nerves are sending their messages correctly to the brain.

How is an evoked potential test done?

We start by measuring your head and then gently rub certain points on the scalp with some gel, before attaching some small metal discs to your head using a sticky paste. We use long wires to connect the metal discs to a computer to record your brain waves.

To test visual evoked potentials, we will ask you to concentrate on a TV screen with changing pictures on.

To test somatosensory evoked potentials, a harmless electrical impulse will be given to your hand or foot. You will feel a tingling or tapping sensation, which may cause nearby muscles to twitch.

To test brainstem auditory evoked potentials, we will ask you to wear some headphones and listen to a clicking noise. Tests will be carried out in the neurophysiology department at Royal Free Hospital on the first floor, behind clinic 2.

Before the test

Please ensure that your hair is clean and free from grease, hairspray, gel or any other hair products including weaves. If you normally wear glasses, please bring these with you for the test.

After your test

The results of your test will be sent to the clinician who requested the test. We will not be able to provide a report on the day of the test as the study needs to be analysed.

Risks and side-effects

Evoked potentials are very safe tests, which usually have minimal or no side effects.

A small number of patients have allergic skin reactions. If you are sensitive to cosmetics, lotions or sticky tape please inform the physiologist performing your test.