(Evoked Brain Potentials, Evoked Responses, Visual Evoked Response [VER], Brainstem Auditory Evoked Response [BAER], Auditory Brainstem Evoked Potentials [ABEP] or alternatively termed Brainstem Auditory Evoked Potentials [BAEP], Somatosensory Evoked Response [SER or SSEP])
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 doctor to interpret.
Evoked potentials studies involve three major tests that measure response to visual, auditory, and electrical stimuli.
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.
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 sometimes confirm a diagnosis of multiple sclerosis.
There may be other reasons for your doctor to recommend an evoked potentials test.
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 on your specific medical condition. Be sure to discuss any concerns with your doctor 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:
An evoked potentials test may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.
Generally, the evoked potentials test follows this process:
Visual evoked response:
You will be seated about three feet away from a screen.
Electrodes will be placed 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 close one eye at a time while the screen displays a checkerboard pattern. The squares of the checkerboard reverse color once or twice a second.
Brain stem auditory evoked response:
You will sit in a soundproof room and be asked to wear earphones.
Electrodes will be placed on top of your head and on one earlobe and then the other.
A clicking sound or another auditory stimulus will be delivered through the earphones to the ear being tested while a “masking” noise will be delivered to the other ear to shield it from the stimulus.
Somatosensory evoked response:
Electrodes will be placed on the scalp and at one or more locations on your body, such as the wrist, back of the knee, or the lower back.
Minute, painless electrical shocks will be delivered through the electrodes placed on the body.
Once the test is complete, the electrodes will be removed and the electrode paste washed off. In some cases, you may need to wash your hair again at home.
Your doctor will inform you as to when to resume any medications you may have stopped taking before the test.
Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.
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