Evoked potentials, or evoked responses, are tests that record the brain's responses to sound, touch, and light. These tests help to evaluate a number of neurological conditions.

How to Prepare

• The evening before or morning of your appointment, wash and dry your hair, but do not apply any spray, oil, mousse, or cream.
• Please do not wear perfume or apply lotions or oils to your skin.
• If you have contact lenses, glasses, or a hearing aid, please wear them for this test.
• You may eat and drink as usual and remain active right up until the time of your appointment.

What to Expect

For each of these tests, a technologist will use a toothpaste-like gel to position small disks (electrodes) on your scalp and, in some cases, on your earlobes, neck, shoulders, and back. The electrodes will be attached to equipment that records your brain's responses to certain stimuli. Each test takes approximately 60 minutes to perform and is painless. You may resume your normal activities immediately after these tests

Brainstem Auditory Evoked Potential (BAEP): During this test, you will lie in a reclining chair and rest while wearing headphones. The technologist will ask you to relax comfortably or sleep, if possible, while you hear a series of clicking sounds.

Somatosensory Evoked Potential (SSEP): You may be asked to disrobe and put on a hospital gown during the SSEP. In addition to placing electrodes on your scalp, neck, and shoulders, the technologist will place a probe over your wrist or ankle. A series of mild electrical currents will pass through the probe, causing your corresponding thumb or big toe to twitch. Although most people feel momentary discomfort as currents pass through the probe, they usually do not consider this test to be painful.

Visual Evoked Potential (VEP): During the VEP, you will be asked to sit in a chair and watch a television screen displaying a checkerboard pattern.