Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Normally, the brain's nerve cells (neurons) communicate with one another by firing tiny electric signals that pass from cell to cell. The firing pattern of these electric signals reflects how busy the brain is. The location of these signals indicates what the brain is doing, such as thinking, seeing, feeling, hearing, controlling the movement of muscles, etc. A seizure occurs when the firing pattern of the brain's electric signals suddenly becomes very abnormal and unusually intense, either in an isolated area of the brain or throughout the brain.

If the whole brain is involved, the electrical disturbance is called a generalized seizure. This type of seizure used to be called a grand mal seizure. The most easily recognizable symptom of a generalized seizure is the body stiffness and jerking limbs known as tonic-clonic motor activity.

Epilepsy is the condition of being prone to repeated seizures, but this can be any kind of seizures, not just generalized seizures. A person can have a seizure without having epilepsy. Today, seizure disorder is the term used more commonly than epilepsy.

A seizure can be provoked by any situation that seriously disturbs the physical or chemical environment of the brain. Some common triggers include:

  • A severe chemical imbalance in the blood Abnormal levels of blood acids, sodium, calcium or blood sugar (especially in diabetics)

  • Drug reactions Reactions to illegal drugs (crack cocaine, amphetamines and others), anesthetics or prescription medications (penicillin, anti-asthma drugs, anticancer drugs and many others)

  • Drug withdrawal Withdrawal from alcohol or sedatives

  • Medical illnesses Extreme high blood pressure (hypertension), eclampsia (a complication of pregnancy), liver failure, kidney failure, sickle-cell disease, systemic lupus erythematosus (lupus or SLE), and many others

  • A local problem involving the brain Head trauma, developmental brain disorders, stroke, brain tumors, and infections in or near the brain (brain abscess, encephalitis, meningitis)

  • Other causes High fever, sleep deprivation, starvation, flashing lights (even from video games), intermittent noise and, rarely, menstruation

If doctors can successfully treat the physical or chemical disturbance in the brain, the seizure problem often goes away. If not, seizures may return again and again, whenever the underlying problem flares up.

Sometimes, a person will experience an unprovoked generalized seizure, one that occurs for no apparent reason. In some people, this type of seizure may be related to a genetic (inherited) vulnerability that makes the brain cells unusually sensitive to minor changes in the environment. In other cases, seizures may be related to scarring caused by prior head trauma or by a previous stroke, brain tumor or brain infection.

Many people who have one unprovoked seizure never experience a second one. However, if a second seizure occurs, the risk of having a third or even more is about 80 percent. For this reason, doctors often regard the second seizure as a sign of epilepsy.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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