What are Evoked Potential Tests?

Evoked potential tests measure your brain's response to different stimuli, namely sight, sound, or sensation. The tests are commonly done to diagnose conditions like multiple sclerosis, migraines, and tumors, such as those in the brainstem or the ear canal. At the beginning of the test, a computer will be connected to your body using wires with patches and sensors, called electrodes. In addition to measuring and recording your body's electrical responses, this machine also shows the location of any nerve damage. There are four types of evoked potential tests:

  • Visual evoked potential, which tests how your brain reacts to visual stimuli. During the test, electrodes will be applied on your scalp and you will be shown a flashing checkerboard pattern. The electrical signals your brain produces in response to the pattern will be recorded. This test is able to identify issues in the optic nerve and is a helpful tool in diagnosing multiple sclerosis, as optic nerve damage is an early sign of that disease.
  • Auditory evoked potential, which measures how your brain responds to sound. In this test, the electrodes will be applied on your earlobes and on your scalp. Different sounds, such as clicks and tones, will be played through headphones, and your responses to those sounds will be recorded. Aside from hearing loss in children, this test also diagnoses acoustic neuromas, which are noncancerous tumors in the ear canal that affect hearing and balance.
  • Somatosensory evoked potential, which tests how well your brain communicates with your spinal cord and the rest of your body. Faint electrical signals will be sent through electrodes that are applied on your wrist or the back of your knee. Electrodes on your scalp will measure how long it takes for your brain to receive the signals. This evoked potential test is often used to diagnose multiple sclerosis. In addition, since it can identify spinal cord issues, it may also be given to individuals who experience numbness following a spinal injury.
  • Motor evoked potential, which measures how your motor pathways function. These pathways deliver signals from the brain and spinal cord to the motor neurons, which are specialized cells directly responsible for controlling muscles. The test uses a device to send magnetic or electrical pulses to any part of your body. Your response will show if your motor neurons can adequately receive signals from your brain and spinal cord. Because this test detects communication issues in the motor pathways, it is used to diagnose multiple sclerosis, as well as to evaluate stroke recovery.
Each test takes between 30 to 60 minutes to complete, and can be done at the doctor's office. Application and removal of the electrodes do not hurt, but since they are placed on your scalp, you should wash your hair with shampoo and avoid using conditioner or other hair products prior to the test.

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