Jacksonian seizures are associated with a form of epilepsy. Epilepsy involves abnormal activity in the brain that can lead to neurons firing at many times their normal rate. This leads to a kind of electrical "storm" developing in the brain and can lead to temporary impairment to the sensory, motor, and cognitive functions.
Jacksonian seizures are initiated with abnormal electrical activity within the primary motor cortex. They are unique in that they travel through the primary motor cortex in succession, affecting the corresponding muscles, often beginning with the fingers. This is felt as a tingling sensation. It then affects the hand and moves on to more proximal areas. Symptoms often associated with a Jacksonian seizure are sudden head and eye movements, tingling, numbness, smacking of the lips, and sudden muscle contractions. Most of the time any one of these actions can be seen as normal movements, without being associated with the seizure occurring. They occur at no particular moment and last only briefly.
These seizures are named after their discoverer, John Hughlings Jackson, an English neurologist, whose studies led to the discovery of the seizures' initiation point (in the primary motor cortex) in 1863.