Evoked Potentials

A. What is an Evoked Potential?

This is a specialized electrical test that measures the electrical activity of your brain in response to the stimulation of your sensory nerves.

The purpose of the test is to identify and localize where your symptoms are coming from. These symptoms can be:

Take a shower the day of test (night before is okay); do not use any vaseline, lotion. oils, skin conditioners, medicated soap or moisterizing soap
Wear loose fitting clothes; bring shorts to wear with lower extremity tests (feet and legs) (for LSSEP, USSEP only)
Follow your physicians instructions regarding your medication.
Arrive at your scheduled time, being late more than 15 minutes could result in your appointment being rescheduled.

An evoked potential test can be done as an outpatient or during a hospital stay. Generally the test follows this process:

You will be asked to remove any jewelry, clothing, wigs, hair extensions or weaves that may interfere with the test
If you are asked to remove any clothing you will be given a gown or you will be instructed to bring shorts with you to wear during the test.
You will be asked to relax in a reclining chair or lie on an exam table
A technologist will attach the electrodes with paste. The electrode locations will vary based on on the test being performed.

Visual Evoked Potential Procedure:

You will be seated a few feet away from a video monitor
A patch will be placed over one eye while the other eye is tested
The technologist will do a brief vision test (looking at a card or wall mounted sign)
You will be asked to focus on a dot in the center of the TV monitor
The TV monitor will be a checker board pattern changing from black to white, it is important that you stay relaxed and stare at the dot for the entire study. The technologist will give you a break between stimulating left and right eye
Test takes about 45 minutes to one hour to complete

Auditory Evoked Potential Procedure:

You will sit in a quiet room wearing headphones.
A technologist will check your hearing
A technologist will place few electrodes on your head and ears
A clicking sound (auditory stimulus) will be delivered through the earphones to the ear being tested and a masking noise (wooshing sound) in the opposite ear.
Test takes about 45 minutes to one hour to complete

Upper and Lower Somatosensory Evoked Potentials:

A technologist may place electrodes on the scalp, neck, shoulders, back, arms and legs depending on the study ordered.
A small continuous electrical impulse is delivered through electrodes placed on the wrist (USSEP) and on the ankle (LSSEP)
For each of the tests the equipment will detect how long it takes for the impulse to travel from the place where you are being stimulated to the brain. You will not feel the impulse go the whole way, only at the point of stimulation.
Test takes about 45 minutes to one hour to complete

Results from your test are generally completed within 24-48 hours. The results will be communicated back to your physician that ordered the study.