epilepsy, a chronic disorder of cerebral function characterized by periodic convulsive seizures. There are many conditions that have epileptic seizures. Sudden discharge of excess electrical activity, which can be either generalized (involving many areas of cells in the brain) or focal, also known as partial (involving one area of cells in the brain), initiates the epileptic seizure. Generalized seizures are classified as tonic-clonic (grand mal), in which there is loss of consciousness and involuntary contraction of all the muscles of the body, lasting a few minutes; or absence (petit mal), in which there is clouding of the consciousness for about 1 to 30 sec and no falling, with as many as 100 attacks occurring daily. Partial seizures include Jacksonian epilepsy, characterized by jerking in the hand and face on the side opposite the brain activity; and psychomotor seizures, in which there may be localized convulsion with no loss of consciousness, as well as incoherent speech and various involuntary movements of the body. Often these are accompanied by a warning cluster of signs and symptoms called an aura.

The cause is unknown in over half the cases of epilepsy, especially in those with onset under age 20. Predisposing factors in other cases include familial history, head injury, alcohol withdrawal, infections (such as meningitis), and abnormalities (such as tumors) of the brain.

The recording of brain waves by electroencephalography is an important diagnostic test for epilepsy. Other diagnostic technologies include CAT scan and magnetic resonance imaging (MRI). Standard treatment of epilepsy is with anticonvulsive drugs, such as carbamazepine, phenytoin, and valproate; it requires a careful analysis of seizure motor activity, anatomical cause, precipitating factors, age of onset of the disorder, severity, daily rhythms, and prognosis. Some cases of childhood epilepsy (which is often eventually outgrown) have been successfully treated with surgery or a very high-fat "ketogenic" diet. The diet results in a natural buildup of ketones in the body, which appear to inhibit the seizures. First aid, such as cushioning the head, is used to prevent the person from self-inflicted injuries during seizures. With proper medication, most epileptics live normal lives. Repeated seizures that lead to unconsciousness, however, appear to be associated with damage to the hippocampus in the brain and sudden unexpected death.