The nervous system uses electrical energy to carry messages smoothly along nerve cells to the brain. Evoked potentials, or EPs, are electrical signals that are generated by the nervous system in response to sensory stimuli. The systems of nerves that send messages to the brain are called sensory nerve pathways. Damage to the nervous system can affect how well sensory nerves send messages to the brain.
About Evoked Potentials Testing
EP tests measure electrical activity in specific areas of the brain in response to stimulation of specific nerve groups. These computerized tests help to locate the site of nerve damage and evaluate the patient’s condition. There are different types of EP tests, including visual, auditory, and somatosensory evoked potentials.
Each EP test uses a mild stimulus to cause specific nerves to react and send a message to the brain. Electrodes record how the brain and spinal cord respond. These electrodes are placed on the skin or scalp by a paste that easily washes or shampoos off. The responses are analyzed by a computer and printed as a wave pattern. This pattern may reveal certain problems and show where any damage is along the nerve pathway.
Brainstem Auditory Evoked Response (BAER)
The BAER evaluates the nerve pathways from the ears to the brain. Electrodes are attached to your scalp and earlobes. Earphones are then placed over your ears, and you will hear rapid clicking noises. The test takes approximately 20 to 30 minutes.
Visual Evoked Response (VER)
The VER evaluates the visual nervous system from the eyes to the brain. Electrodes are attached to your scalp, and you are asked to stare at a pattern on a video screen. Each eye is tested separately. The test takes approximately 15 minutes.
Somatosensory Evoked Potentials (SSEP)
The SSEP assesses the pathways from the nerves in the arms or legs through the spinal cord to the brain. Electrodes are placed on your scalp and along the spine, and a small electrical current is applied to the skin near nerves on arms or legs. This current creates a tingling sensation, but it is not painful. Each leg or arm is tested separately. This test takes approximately 45 to 60 minutes.