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Evoked Potential Studies

An evoked potentials study measures electrical activity in the brain in response to stimulation of sight, sound, or touch. When the brain is stimulated by sight, sound, or touch, signals travel along the nerves to the brain. There, electrodes detect the signals and display them for neurophysiologist to interpret. Evoked potentials studies involve 2 tests that measure response to visual, and electrical stimuli.

  • Visual evoked response (VER) test. This test can diagnose problems with the optic nerves and other visual pathways in the brain that affect sight. A healthcare provider places electrodes along your scalp. They record the electrical signals as you watch a checkerboard pattern flash for several minutes on a screen.

  • Somatosensory evoked response (SSER) test. This test can detect problems with the spinal cord that cause numbness of the arms and legs. For this test, a healthcare provider attaches electrodes to your wrist, ankles, the back of your knee, neck, or other locations. He or she will apply a mild electrical stimulus through the electrodes. Electrodes on your scalp then determine the amount of time it takes for the current to travel along the nerves to the brain.


They are also done to diagnose disorders of the optic nerve, and to detect tumors or other problems affecting the brain and spinal cord. These tests usually do not lead to a specific diagnosis about what is causing the abnormality. But the evoked potentials test can sometimes confirm a diagnosis of multiple sclerosis.


  • You don't need to fast for this test. You will not receive sedation.

  • Tell your healthcare provider of all medicines (prescribed and over-the-counter) and herbal supplements that you are taking.

  • Wash your hair the night before the test, but do not use conditioner or apply any hairspray or other hair products.

  • Based on your medical condition, your healthcare provider may request other specific preparations.

  • Don't put lotions or cream on your skin if you are getting SSER done.


  • You will be asked to remove any clothing, jewellery, hairpins, eyeglasses, hearing aids, or other metal objects that may interfere with the procedure.

  • If you are asked to remove clothing, you will be given a gown to wear.

  • You will be asked to relax in a reclining chair or lie on a bed.

  • A healthcare provider will attach the electrodes with a paste. The electrodes will be positioned depending on which type of evoked potentials test is being done.

The test will generally proceed as follows.

Visual evoked response:

  • You will be seated a few feet away from a screen.

  • A technician will place electrodes on your scalp over the areas of the brain responsible for interpreting visual stimuli.

  • You will be asked to focus your gaze on the center of the screen.

  • You will then be asked to focus on a screen that displays a checkerboard pattern. The squares of the checkerboard reverse color once or twice a second. You will usually wear an eye patch to test one eye at a time.

Somatosensory evoked response:

  • A technician will place electrodes on the scalp and at one or more locations on your body, such as the wrist, back of the knee, or the skin over your spine.

  • Small, painless electrical shocks will be sent through the electrodes placed on the body.

  • For each of the tests, the electrical activity detected by the electrodes on the scalp will be fed into a recorder. The recorder amplifies the signal and charts it so that your healthcare provider can interpret the results.