What is an Evoked Potential Test?

An evoked potential test is a noninvasive medical test used to see how long it takes for nerves to respond to stimuli. This type of test may be used in the diagnosis of patients believed to have neurological disorders like multiple sclerosis. It can also be used in brain surgery. The test is painless and usually patients do not have to observe any special precautions before they take it. Results may be available on the same day or at a future medical appointment.

In an evoked potential test, electrodes are attached to the head to monitor electrical activity in the brain. Patients are usually asked to have their hair dry and unstyled for the test. Once the electrodes are in place, a stimulus can be presented. Auditory tests use tones in headphones, visual tests use flashed visual stimuli, and somatosensory tests use small electrical pulses.

The patient does not need to respond to the stimuli on a conscious level during the evoked test, merely to sit in a relaxed position. As the brain responds to the stimuli, electrical activity will occur and the time between the presentation of the stimuli and the response can be measured. In people with neurological conditions, there may be a delay caused by poor nerve conduction and other problems. After the test is over, the patient can go home.

If the patient's neurologist conducts the test, it may be possible to discuss the results immediately. In other cases, a technician will prepare the test results for review by a neurologist and the patient will need to meet with the doctor to talk about the outcome of the evoked potential test. These tests can be used in the diagnosis of patients with suspected neurological conditions as well as in ongoing monitoring of patients with progressive diseases to look for signs of changes, including signs that the patient is responding to treatment.

An evoked potential test can also be used in brain surgery. Doctors who are operating on the brain use a variety of techniques to monitor patients to ensure they are in the right spot and to confirm they are not causing damage. With an evoked potential test, a neurosurgeon can map out different areas of the brain while working, confirm the placement of devices in the brain, and check on the patient's status. If signs of complications start to appear, the surgeon can make adjustments to compensate.