As U.S. Sen. Edward Kennedy recovers from what his office has identified as a seizure, questions linger about his overall health -- and what these reported seizures may indicate.
Below are some of the more frequently asked questions about seizures.
What Is a Seizure?
The National Institutes of Health defines a seizure as a sudden change in behavior due to excessive electrical activity in the brain.
The nature of this change in behavior may vary widely depending on what parts of the brain are affected. While some seizures may lead to loss of consciousness, often accompanied by convulsions, less noticeable seizures may bring about little more than a prolonged staring spell. On occasion, seizures can cause visual disturbances and abnormal sensations.
Doctors classify a seizure in which the sufferer maintains consciousness as a "simple" seizure, while those that result in loss of consciousness are called "complex" seizures.
Seizures can also be categorized in terms of how much of the body is affected; "generalized" seizures affect the entire body, while "focal" seizures affect only one side of the body.
What Causes Seizures?
Seizures in general are brought about by an abnormal surge of activity within the brain's cerebral neurons. Some doctors have likened the condition to an "electrical storm" within the brain.
It may be a fitting analogy, since in the same way that electrical storms can overwhelm the circuitry of electronics and household appliances, a seizure can interfere with the brain's sensitive circuitry, albeit temporarily.
There are many possible causes for seizures. While they are most often associated with the neurological condition epilepsy, even those who do not have epilepsy may experience them.
Injury or trauma to the head can lead to an increased risk of seizure -- a fact that may be relevant with regard to Kennedy, who sustained serious injuries in a plane crash in 1964. Seizures are also known to accompany alcohol withdrawal, low blood sugar, certain infections, brain tumors and other medical conditions. Likewise, some seizures are also known to be linked to stroke.
Are There Warning Signs for Seizure?
Occasionally, people who are about to have a seizure experience warning signs leading up to the event. Hours, or even days, before a person experiences a full-blown seizure, he or she may experience a prodrome, commonly referred to as an "aura." This phase often involves anxiety, irritability, difficulty concentrating or sleep disturbances.
However, in many cases seizures strike without warning. Most seizures are self-limiting; they eventually run their course. The danger lies in the fact that an individuals having seizures are often in situations that put them at risk of injuring themselves.
What Comes Next for Kennedy?
Kennedy's office reports that he will be undergoing a series of medical tests.
Dr. Mike Walker, former director of the Division of Stroke, Trauma, Neurodegenerative Disease at the National Institutes of Health, told ABC News that doctors will likely conduct brain imaging tests, such as computerized tomography (CT) and magnetic resonance imaging (MRI) to rule out a tumor as the cause of the seizures and determine if there is good blood flow to Kennedy's brain.
Walker adds that an electroencephalogram (EEG) will be performed to measure the senator's brain activity and determine whether there are any abnormalities. Kennedy will also likely undergo blood tests, brain scans and tests to determine whether his heart is functioning normally.