Evoked potential

Evoked potential testing measures the time it takes for your nerves to respond to stimulation. This might include visual, auditory or somatosensory (involving the nerves in your arms and legs) testing.

Responses are measured by looking at brain waves via electrodes taped to your head.

Why would an evoked potential be recommended?

Evoked potential testing can detect certain neurological conditions and damage to the optic or auditory nerve. For example, this test may be used to diagnose or rule out multiple sclerosis when a neurological examination alone doesn’t provide enough evidence.

How do you prepare for evoked potential testing?

Typically you don’t need to do anything to prepare. If you’re having visual testing, you’ll want to bring or wear your corrective lenses.

What can you expect during evoked potential testing?

Electrodes will be applied based on the type of response that’s being sought. Your skin will be prepped with a gritty gel to ensure the best contact with your skin. Electrodes will then be pasted on and secured.

Your brain will be stimulated in one or more of the following ways:

  • Visual: To test the optic nerve pathway each of your eyes will be covered with a patch, one at a time, and you’ll be presented with a black-and- white checkerboard pattern and LED goggles, or a strobe light may be used. This test is typically performed if you’re reporting blurry or diminished vision. You won’t feel any pain or discomfort, but one or both eyes may become fatigued. The test will take 30 to 60 minutes.
  • Auditory: To see how well the auditory nerve conducts signals you’ll lie down and wear headphones. Once you’re comfortable, you’ll hear a clicking noise in the ear being stimulated and “white noise” in the opposite ear. The test is not painful and will last about an hour. You may even fall asleep during the testing.
  • Somatosensory: This is performed on the nerves feeding the upper and/or lower extremities. Electrodes may be placed on your scalp, cervical spine, collarbone area, lower spine or knee. You’ll lie quietly with your eyes closed as you feel electrical pulses on your wrist or ankle, depending on which nerve is being tested. Responses are recorded from the peripheral nerve, spinal cord and central nervous system as the signal travels up the limb and spine and ultimately reaches the brain. The test will take about 20 minutes for each limb tested. The more you can relax and lie still, the quicker the testing will go.

Your responses to these stimuli will be recorded, with particular attention paid to the time between the stimulation and your response to it. Usually only one of these studies will be ordered; the visual test is the most common.

All evoked potential studies are performed using American Clinical Neurophysiologic Society guidelines.