When there is an abnormal discharge of electrical energy in certain brain cells, the result is

In generalized-onset seizures, the seizure begins in both sides of the brain. Most generalized-onset seizures impair awareness. They often cause loss of consciousness and abnormal movements, usually immediately. Loss of consciousness may be brief or last a long time.

Generalized-onset seizures include the following types:

• Tonic-clonic seizures (formerly, called grand mal seizures)

• Clonic seizures (involving sustained rhythmic jerking of muscles after muscles stiffen)

• Tonic seizures (involving stiffening of muscles in all limbs)

• Atonic seizures (involving loss of muscle tone)

• Myoclonic seizures (involving rhythmic jerking of muscles not preceded by stiffening of muscles)

• Myoclonic-tonic-clonic seizures (involving jerking of muscles followed by muscle stiffening and repeated jerking of muscles), including juvenile myoclonic epilepsy

• Myoclonic-atonic seizures (involving jerking of muscles, followed by loss of muscle tone)

• Epileptic (infantile) spasms

Most types of generalized seizures (such as tonic-clonic seizures) involve abnormal muscle contractions. Those that do not are called absence seizures.

Generalized-onset seizures begin with abnormal discharges in a deep, central part of the brain and spread simultaneously to both sides of the brain. There is no aura. The seizure typically begins with an outcry. People then become unaware or lose consciousness.

During generalized-onset seizures, particularly generalized tonic-clonic seizures, people may do the following:

• Have severe muscle spasms and jerking throughout the body as muscles rapidly and repeatedly contract and relax

• Bite their tongue (often occurs)

• Drool or froth at the mouth

• Lose control of the bladder and/or bowels

The seizures usually last 1 to 2 minutes. Afterward, some people have a headache, are temporarily confused, and feel extremely tired. These symptoms may last from minutes to hours. Most people do not remember what happened during the seizure.

In generalized tonic-clonic seizures, muscles contract (the tonic part), then rapidly alternate between contracting and relaxing (the clonic part). These seizures may be

• Generalized-onset (starting in both sides of the brain)

• Focal to bilateral (starting in one side of the brain and spreading to both sides)

In both types, consciousness is temporarily lost and a convulsion occurs when the abnormal discharges spread to both sides of the brain.

Focal-to-bilateral tonic-clonic (grand mal) seizures usually begin with an abnormal electrical discharge in a small area of one side of the brain, resulting in a focal aware or focal impaired-awareness seizure. The discharge then quickly spreads to both sides of the brain, causing the entire brain to malfunction. Symptoms are similar to those of generalized-onset seizures.

Atonic seizures occur primarily in children. They are characterized by a brief but complete loss of muscle tone and consciousness. They cause children to fall to the ground, sometimes resulting in injury.

In clonic seizures, the limbs on both sides of the body and often head, neck, face, and trunk jerk rhythmically throughout the seizure. Clonic seizures usually occur in infants. They are much less common than tonic-clonic seizures.

Tonic seizures occur commonly during sleep, usually in children. Muscle tone increases abruptly or gradually, causing muscles to stiffen. The limbs and neck are often affected. Tonic seizures typically last only 10 to 15 seconds but can cause people, if standing, to fall to the ground. Most people do not lose consciousness. If seizures last longer, muscles may jerk a few times as the seizure ends.

Atypical absence seizures (see below), atonic seizures, and tonic seizures usually occur as part of a severe form of epilepsy called Lennox-Gastaut syndrome, which begins before children are 4 years old.

Myoclonic seizures are characterized by quick jerks of one or several limbs or the trunk. The seizures are brief and do not cause loss of consciousness, but they may occur repetitively and may progress to a tonic-clonic seizure with loss of consciousness.

In myoclonic-atonic seizures, the limbs or trunk jerks briefly, then goes limp (drop attack). Seizures usually begin between the ages of 6 months to 6 years. Before the first myoclonic-atonic seizure, two thirds of children have febrile seizures and generalized-onset convulsive seizures. Development and mental processes are typically normal, but during or after the seizure, development and thinking may be impaired.

Juvenile myoclonic epilepsy typically begins during adolescence. Typically, seizures begin with quick jerks of both arms. About 90% of these seizures are followed by generalized tonic-clonic seizures. Some people also have absence seizures. The seizures often occur when people awaken in the morning, especially if they are sleep-deprived. Drinking alcohol also makes these seizures more likely.

Absence seizures do not involve abnormal muscle contraction. They may be classified as

• Typical (formerly called petit mal)

Typical absence seizures usually begin in childhood, usually between the ages of 5 and 15 years, and do not continue into adulthood. However, adults occasionally have typical absence seizures. Unlike tonic-clonic seizures, absence seizures do not cause convulsions or other dramatic symptoms. People do not fall down, collapse, or move jerkily. Instead, they have episodes of staring with fluttering eyelids and sometimes twitching facial muscles. They typically lose consciousness, becoming completely unaware of their surroundings. These episodes last 10 to 30 seconds. People abruptly stop what they are doing and resume it just as abruptly. They experience no after-effects and do not know that a seizure has occurred. Without treatment, many people have several seizures a day. Seizures often occur when people are sitting quietly. Seizures rarely occur during exercise. Hyperventilation can trigger a seizure.

Atypical absence seizures differ from typical absence seizures as follows:

• Jerking and other movements are more pronounced.

• People are more aware of their surroundings.

Most people with atypical absence seizures have neurologic abnormalities or developmental delays. Atypical absence seizures usually continue into adulthood.