(Evoked Brain Potentials, Evoked Responses, Visual Evoked Response [VER], Brainstem Auditory Evoked Response [BAER], Auditory Brainstorm Evoked Potentials [ABEP], Somatosensory Evoked Response [SER])
What is an evoked potentials study?
Evoked potentials studies measure electrical activity in the brain in response to stimulation of sight, sound, or touch. Stimuli delivered to the brain through each of these senses evoke minute electrical signals. These signals travel along the nerves and through the spinal cord to specific regions of the brain and are picked up by electrodes, amplified, and displayed for a physician to interpret.
Different types of evoked potentials studies:
Evoked potentials studies involve three major tests that measure response to visual, auditory, and electrical stimuli.
visual evoked response (VER) test - can diagnose problems with the optic nerves that affect sight. Electrodes are placed along the scalp. The patient is asked to watch a checkerboard pattern flash for several minutes on a screen, and the electrical responses in the brain are recorded.
brainstem auditory evoked response (BAER) test - can diagnose hearing ability and can indicate the presence of brain stem tumors and multiple sclerosis. Electrodes are placed on the scalp and earlobes. Auditory stimuli, such as clicking noises and tones, are delivered to one ear.
somatosensory evoked response (SSER) test - can detect problems with the spinal cord as well as numbness and weakness of the extremities. For this test, electrodes are attached to the wrist, the back of the knee, or other locations. A mild electrical stimulus is applied through the electrodes. Electrodes on the scalp then determine the amount of time it takes for the current to travel along the nerve to the brain.
A related procedure that may be performed is an electroencephalogram (EEG). An EEG measures spontaneous electrical activity of the brain. Please see this procedure for additional information.
Reasons for the Procedure
Evoked potential studies may be used to assess hearing or sight, especially in infants and children, to diagnose disorders of the optic nerve, and to detect tumors or other problems affecting the brain and spinal cord. The tests may also be performed to assess brain function during a coma.
A disadvantage of these tests is that they detect abnormalities in sensory function, but usually do not produce a specific diagnosis about what is causing the abnormality. However, the evoked potentials test can confirm a diagnosis of multiple sclerosis.
There may be other reasons for your physician to recommend an evoked potentials test.
Risks of the Procedure
The evoked potential studies are considered safe procedures. The tests cause little discomfort. The electrodes only record activity and do not produce any sensation.
There may be risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.
Certain factors or conditions may interfere with the results of the test. These include, but are not limited to, the following:
presence of earwax or inflammation of the middle ear
severe hearing impairment
muscle spasms in the head or neck
Before the Procedure
Your physician will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.
Generally, no prior preparation, such as fasting or sedation, is required.
Wash your hair the night before the test, but do not use conditioner or apply any hairspray or other hair products.
Based upon your medical condition, your physician may request other specific preparation.