Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

The brain's nerve cells (neurons) communicate by firing tiny electric signals. During a seizure (convulsion), the firing pattern of these electric signals suddenly changes. It becomes unusually intense and abnormal.

A seizure can affect a small area of the brain. Or it can affect the entire brain. If the whole brain is involved, it is called a generalized seizure.

The two most common forms of generalized seizures are:

  • Generalized seizures (grand mal seizures)

  • Absence seizures (petit mal seizures)

Both forms of generalized seizures cause a temporary loss of consciousness.

An absence seizure causes a loss of consciousness for 30 seconds or less. It is barely noticeable, if at all. The person simply stops moving or speaking. He or she stares straight ahead blankly, and does not respond to questions. The seizure is short and hard to notice. A person can have 50 or 100 absence seizures a day, without them being detected.

When the absence seizure ends, the person goes back to his or her normal activities. He or she does not realize that anything has happened.

Epilepsy is a brain disorder that causes recurrent seizures if it is not treated. A child with repeated absence seizures is said to have childhood absence epilepsy or petit mal epilepsy.

Absence epilepsy can begin at any time during childhood. Most often it starts between the ages of 4 and 15 years.

In most cases, the reason for the seizures is unknown. Genetic (inherited) factors may play some role in the development of absence 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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