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Just as the EEG measures ongoing brain electrical activity, so Evoked Potentials (or EPs) measure electrical activity produced by external stimuli (e.g., light flashes, sound clicks). EPs are done to test the auditory pathways (brain stem auditory evoked potentials), visual pathways (visual evoked potentials), and the somatosensory pathways (somatosensory evoked potentials). These are especially useful for testing younger, uncooperative, or non-communicative patients, especially the auditory and visual pathways of infants. These studies are also done during various surgical procedures, such as spinal surgery, to protect the nervous system.
EP studies require placing EEG-like recording electrodes on the scalp and stimulating the appropriate pathways. Visual evoked potentials are done by either looking at a changing checkerboard pattern or at a flashing light. Auditory evoked potentials are done by stimulating the auditory system with a clicking noise. Special auditory EP techniques allow a determination of whether poor hearing results from inner ear, nerve to the ear, or brain problems. Somatosensory evoked potentials are done by giving a small electrical impulse to the extremities. Infants and younger children may require sedation for these studies. A special evoked potential, called the frequency modulated steady-state evoked potential (FM-SSAEP) is useful in the evaluation and treatment of Landau-Kleffner Syndrome and other language disorders, usually done as part of the qEEG or BEAM study. EPs are often performed as part of our inpatient epilepsy service to assist in better localization of cortical (brain) function.
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Evoked Potentials - EPs
