| A test in which the brain’s electrical activity in response to visual stimuli (e.g., a flashing checkerboard) is recorded by an electroencephalograph and analysed by computer. Demyelination results in a slowing of response time. Because this test is able to confirm the presence of a suspected brain lesion (area of demyelination) as well as identify the presence of an unsuspected lesion that has produced no symptoms, it is extremely useful in diagnosing MS. VEPs are abnormal in approximately 90 percent of people with MS. |