Jacksonian seizure: A form of epilepsy involving brief alteration in movement, sensation or nerve function caused by abnormal electrical activity in a localized area of the brain. Jacksonian seizures is a form of simple complex seizures in which the abnormal electrical activity is localized to one region in the brain. Seizures of this type typically cause no change in awareness or alertness. They are transient, fleeting, and ephemeral.
Jacksonian seizures are extremely varied and may involve, for example, apparently purposeful movements such as turning the head, eye movements, smacking the lips, mouth movements, drooling, rhythmic muscle contractions in a part of the body, abnormal numbness, tingling, and a crawling sensation over the skin.
These seizures are named for the English neurologist, John Hughlings Jackson, who studied speech defects in brain disorders and confirmed the location in the brain of the speech center ("Broca's center"). He described what are today called Jacksonian seizures in 1863 and in 1875 found the areas in the brain that caused them. Jackson was among the towering figures of 19th-century medicine, one of "the great men of medicine." (There were few, if any, women in medicine in the 19th century.)