There is a fine balance in the brain between factors that begin electrical activity and factors that restrict it, and there are also systems that limit the spread of electrical activity. During a seizure, these limits break down, and abnormal electrical discharges can occur and spread to whole groups of neighboring cells at once. This linkage of electrical discharges creates a "storm" of electrical activity in the brain. This is a seizure. When a person has had at least two of these seizures, that's called epilepsy.

How does epilepsy begin?

The reasons why epilepsy begins are different for people of different ages. But what's true for every age is that the cause is unknown for about half of everyone with epilepsy.

Children may be born with a defect in the structure of their brain, or they may suffer a head injury or infection that causes their epilepsy. Severe head injury is the most common known cause in young adults. In middle age, strokes, tumors, and injuries are more frequent. In people over 65, stroke is the most common known cause, followed by degenerative conditions such as Alzheimer's disease.

Why does it sometimes take years before someone with a brain injury experiences a seizure?

Often seizures do not begin immediately after a person has an injury to the brain. Instead, a seizure may happen many months later. We do not have a good explanation for this common observation, but scientists are actively researching this subject.

Topic Editor: Steven C. Schachter, M.D.
Last Reviewed:12/15/06

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