During normal waking and sleeping, your brain cells produce various electrical discharge patterns. If the electrical discharges by your brain cells become abnormally synchronized, a convulsion or seizure occurs. The abnormal firing of your brain cells can remain localized to a small area or can spread rapidly to involve your entire brain.

Often, the cause of a seizure is unknown. Some of the known causes of seizures include:

• Metabolic disturbances. Diseases of the kidney or liver can cause chemical disturbances in your body, as can very low levels of sodium, calcium or magnesium.

• Previous brain trauma. A traumatic head injury, such as those sustained in automobile accidents or serious sports injuries, can cause seizures.

• Vascular system problems. Blood vessel disorders and strokes are a common cause of seizures for older adults.

• Toxic substances. Using drugs or other chemicals or withdrawing from addicting substances, especially alcohol, can affect your brain's electrical activity and your nervous system.

• Infection. An inflammation of your brain, such as that caused by meningitis or encephalitis, may trigger a seizure.

• Birth defects. Congenital malformations in the brain can be responsible for seizures in infants and young children.

• Brain tumor. Although a brain tumor is an uncommon cause, a seizure may be the first indication of a brain tumor.