The Evoked Potential (EP) is a recording of electrical activity from the brain, spinal nerves, or sensory receptors in response to specific external stimulation, whether it be visual, auditory, or sensory stimulation. Electrodes are applied to the scalp and other areas of the body, and a series of stimulations are introduced. A computer then records the neurological responses. Hundreds, sometimes thousands, of responses are received, amplified, and averaged by the computer. The final response is then printed on a graph and interpreted by a physician who looks for particular waveforms and the latency. Evoked Potentials are helpful in evaluating a number of different neurological problems including spinal cord injuries, acoustic neuroma, and optic neuritis. Each type of EP looks at a different neurological pathway. The most common types of EPs are:
Auditory
The Brainstem Auditory Evoked Potential (BAEP) assists in evaluating the auditory nerve pathways from the ears through the brainstem. Earphones deliver a series of clicks or tones to each ear separately.
Visual
Visual Evoked Potentials (VEPs) evaluate the visual nervous system from the eyes to the occipital (visual) cortex of the brain. The patient is usually asked to look at a pattern on a video screen while remaining fully alert. Each eye is tested separately.
Somatosensory
Somatosensory Evoked Potentials (SSEPs) assess pathways from nerves in the arms or legs, through the spinal cord to the brainstem or cerebral cortex. A small electrical current is applied to the skin overlying nerves on the arms or legs. The current creates a tingling sensation, but is not painful. Each leg or arm is tested separately.