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Evoked potentials

What are Evoked Potentials?

These are recordings of electrical signals produced naturally by your brain following repeated stimulation of the eyes, ears or  arms and legs. Evoked Potentials (or EPs) is the name of a group of tests described below. The time taken for the tests varies. The Physiologist starts by attaching a number of small metal discs to your head, using a sticky paste. Please ensure your hair is dry, clean and free from grease, hair spray and lacquers etc. Loose clothing will be most comfortable. You may wear jewellery but it may have to be removed if it gets in the way. After the test the discs are removed and any paste left in the hair can be washed out with shampoo.

What are Visual Evoked Potentials (VEPs)?

These are tests of the pathway between the eye and the back of the brain. You will be asked to look at the centre of a television screen that has a moving black and white chequer-board pattern. Each eye is tested separately, with a patch covering the eye that is not being investigated. This is a painless procedure and there are no after effects. The time taken for this test can be 45 to 60 minutes to complete. If you wear glasses please bring them along for the test.

What are Somatosensory Evoked Potentials (SSEP)?

These are tests of the pathways from the arm or leg through the spinal cord to the brain. An electrical stimulator is used to pass brief electrical currents to your nerves. This causes a tingling sensation and there may be small twitches of your hand and feet. This can be a little uncomfortable, but should not be painful. There are no after effects. The time taken for this test can be 1 to 2 hours.