Evoked potentials (EP) are a type of study that is recorded by averaging the EEG activity after the presentation of a time-locked stimulus. Evoked potentials are also sometimes called evoked response testing too. They can be performed by visual, auditory, or electrical (somatosensory) stimulation of nerves in the arms or legs. Usually, just one of the types of studies is ordered and it is unlikely that you would have two or all three modalities performed. The visual evoked potential (VEP/VER) is by far the most common EP performed in a diagnostic testing lab. Somatosensory evoked potentials (SSEP’s) are performed occasionally in the lab setting and are very often performed during neurologic and orthopedic surgeries to monitor the integrity of the nerve pathway. Brainstem auditory evoked potentials (BAEP/BAER) are rarely performed in the lab. Our evoked potential studies are performed using American Clinical Neurophysiologic Society (ACNS) guidelines.

The study is performed by placing flat disk type electrodes over specific anatomic locations and depending on what type of study performed, electrodes may be placed on the scalp, cervical spine, collarbone area (brachial plexus), lower spine, and knee area (popliteal fossa). The number of electrodes placed is dependent on the type of study being performed.

The technician/technologist will take just a few measurements on the scalp. The skin will be prepped with a skin preparation that feels gritty or scratching to help make a better contact with the skin. Electrodes will then be pasted on with conductive cream and secured. The technician/technologist will check the connections of all the electrodes to insure good conductivity.

The study eventually produces waveforms that are measure and interpreted by one of our neurologists.

Visual Evoked Potential

The VEP (VER) tests the optic nerve pathway to see how fast the signal travels through the brain to the visual receptive area located in the back of the brain (occipital lobe). There are several ways to stimulate the optic nerve and the most common method will be for one of your eyes to be covered with a patch and then you will watch a checkerboard pattern of black and white squares. The number of recording electrodes placed on your scalp may vary but typically six are used. The technologist will check your vision with a vision card. There are other types of stimulation techniques sometimes employed and they may consist of LED goggles or some type of a photic flash stimulator.

VEP’s are usually performed because of blurry vision or diminished vision, or a known history of optic neuritis.

You can expect to sit in a darkened room, focusing at the checkerboard pattern with one eye at a time. The technologist will give you a brief rest period several times throughout the testing and, eventually, the other eye will be tested. It is important for you to bring or wear corrective lenses, particularly if you are near-sighted (can’t see far away) and to sit quietly and relaxed while looking at the monitor.

During the VEP you will not feel any pain or discomfort although your eye may become a bit fatigued. Sometimes the checkerboard pattern may be changed in some way and repeated. Typically the test is usually about 45 minutes from the time you enter the lab until testing is completed. It may take up to 1 hour. Occasionally, the test may go very quickly and be completed in 30 minutes or less.

The study produces waveforms from each site examined. Once completed, the technologist will wipe the paste out of your hair. The study will be interpreted by one of our physicians and a report will be given to your doctor. Your doctor or provider will contact you with the results.

Brainstem Auditory Evoked Potentials

BAEP’s are performed to see how well the auditory nerve is conducting signals that travel after the cochlea is stimulated through the brain and brainstem. Headphones will be placed on your head for stimulation of the nerve and you will hear a clicking noise in the ear being stimulated and a “white noise” in the opposite ear. Each auditory nerve is stimulated individually.

The procedure is performed by placing four electrodes on the scalp and either the mastoid or earlobes. The skin will be prepped with a skin preparation that feels gritty or scratching to help make a better contact with the skin. Electrodes will then be pasted on with conductive cream and secured. The technician/technologist will check the connections of all the electrodes to insure good conductivity. The technologist will establish your hearing threshold by gradually increase the clicking noise in the headphones and ask you when you first start to hear the clicking sound.

You can expect to lie down on an exam table and the technologist will try to make you as comfortable as possible. The lights will be lowered and you will be asked to try to be as relaxed as possible and lay relatively quiet and still. The stimulus will be turned up louder in the ear being stimulated. You will hear the clicking sound for approximately 10-15 minutes. It is okay if you fall asleep. Later, the clicking sound will be switched to the opposite ear and this process is repeated. In order to obtain the best possible quality study, a different type of clicking or increased decibel level may be employed and the test repeated.

You will experience no pain or discomfort during the testing and test time is typically one hour or less. Once completed, the technologist will wipe the paste out of your hair. The study will be interpreted by one of our physicians and a report will be given to your doctor. Your physician or provider will contact you with the results.

Somatosensory Evoked Potentials

The Somatosensory Evoked Potential (SSEP) is sometimes known as the somatosensory evoked response (SSER) and may be performed on nerves of either the upper or lower extremities. They are customarily done on both sides and your physician may order just both arms or legs, and sometimes, all four extremities. The sensory nerves in the extremities (peripheral nerves) are stimulated and responses are recorded from both the peripheral nerve, spinal cord and central nervous system as the signal travels up the limb, the spine and ultimately reaching the cerebral cortex (brain).

The study is performed by placing flat disk type electrodes over specific anatomic locations and depending on what type of study performed, electrodes may be placed on the scalp, cervical spine, collarbone area (brachial plexus), lower spine, and knee area (popliteal fossa). The number of electrodes applied is dependent on the type of study being performed.

The technician/technologist will take just a few measurements on the scalp. The skin will be prepped with a skin preparation that feels gritty or scratchy to help make a better contact with the skin at each recording site. Electrodes will then be pasted on with conductive cream and secured. The technician/technologist will check the connections of all the electrodes to insure good conductivity.

Once the technologist has made you comfortable and the electrodes have been connected to the instrument you will start to feel a little electrical pulsing sensation at your wrist or ankle (depending on which nerve is being tested). This will be increased little by little until ideally it produces a small motor twitch. This sensation feels strange and is difficult to describe. Particularly in the lower extremities, you may find it annoying or uncomfortable.

It is very important to lie quietly with your eyes closed in a relaxed state as this helps the procedure go more quickly. During this time several thousand repetitions may occur and the information must be replicated for accuracy. It may take up to approximately 20 minutes for each limb tested and is completely dependent on your ability to relax and lay still. If you are having all four limbs tested, your testing time may last up to three hours.

The study eventually produces waveforms that are measured and interpreted by one of our neurologists.

Once completed, the technologist will wipe the paste from the electrode sites. The study will be interpreted by one of our physicians and a report will be given to your doctor. Your physician or provider will contact you with the results.

Outside Physician Requests

If you would like to schedule a procedure with our office, please fax patient demographic information (including insurance), most recent patient history and physician notes along with an authorization if needed to our office at 602-258-3368. Our technologist or office staff member will contact the patient for scheduling

Should you have any questions regarding electroneurodiagnostic testing, feel free to contact our technologist, Renee Schwarz, R. EEG/EP T., C.M.E.T., R.NCST, CNCT, at 602-258-3354 at extension 132.