Neurodiagnostics

What to Expect with an Evoked Potential Study

Electrodes are applied to the scalp and other areas of the body, commonly the legs and arms. A series of stimuli is introduced, and a computer records the neurological responses. Hundreds of responses are received, amplified and averaged by a computer. The final response is plotted and graphed by computer and interpreted by physicians who analyze the waveforms and their speed of transmission.

There are different types of EP which evaluate different parts of the brain or spinal cord. Common examples include brainstem auditory evoked potential (BAER), visual evoked potential (VEP) and somatosensory evoked potential (SSEP).

• Auditory: The BAER helps in evaluating the auditory nerve pathways from the ears through the lower portion of the brain. Electrodes are attached to the scalp and earlobes, and earphones are placed over the ears. The earphones deliver a series of clicks or tones to each ear separately.
• Visual: VEPs evaluate the visual pathways of the nervous system from the eyes to the occipital (visual) cortex of the brain. Electrodes are applied to the scalp, and the patient is asked to focus on a pattern on a video screen while remaining fully alert. Each eye is tested separately.
• Somatosensory: SSEPs assess pathways from nerves in the arms or legs, through the spinal cord, to the brainstem or cerebral cortex. Electrodes are placed on the scalp, along the spinal cord and along the arms or legs. A small electrical current is then applied to the skin overlying nerves on the arms or legs. The current creates a tingling sensation but is usually not painful. Each arm or leg is tested separately.