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An EP is a recording of electrical activity form the brain, spinal nerves or sensory receptors in response to specific external stimulations. Electrodes are applied to the scalp and other areas of the body; then a series of stimuli is introduced and a computer records the neurological responses. Hundreds of responses or received, amplified and averaged by a computer. The final response is plotted on a graph and interpreted by a physician who looks for particular waveforms and the time it takes them to occur. The three most common types are the brainstem auditory evoked potential (BAER), The visual evoked potential (VEP), and the somatosensory potential (SSEP).
The BAER assists in evaluating the auditory nerve pathways from the ears through the brainstem. Electrodes are attached to the slap and earlobes, and earphones are placed over the ears. The phones deliver a series of clicks or tones to each ear separately.
VEPs evaluate the visual nervous system from the eyes to the occipital (visual)cortex of the brain. Electrodes are applied to the scalp and the patient is usually asked to stare at a pattern on a video screen while remaining fully alert. Each eye is tested separately.
SSEP assess pathways from nerves in the arms and legs, through the spinal cord, to the brainstem or cerebral cortex. Electrodes are placed on the scalp and along the spinal cord and a small electrical current is then applied to the skin overlying nerves on the arms or legs. The current creates a tingling sensation, but it is not painful. Each leg or arm is tested separately.