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  A Storm in the Brain


by Daniel Pendick
Copyright 2001 Memory Loss and the Brain

To many, the word "epilepsy" calls to mind an image of a person lying prostrate on the floor with teeth clenched, jerking with involuntary muscle spasms. But epilepsy has many faces. Some types of seizures trigger convulsions, whereas others unfold with more subtle signs-a repeated arm movement or facial twitch, for example. Regardless of how epilepsy shows itself on the outside, on the inside the person is undergoing a kind of storm in the brain, one that frequently results in memory loss. Researchers are beginning to identify the range of memory impairments associated with epilepsy and link them to specific areas of the brain. That knowledge could lead to better treatments and assist in the rehabilitation of people whose memories have been impaired by seizures.



© Chad Baker
 
 

Brainstorming

Seizures are short periods of abnormal electrical activity in the brain that happens when large numbers of brain cells (neurons) begin to fire uncontrollably, like a cluster of madly blinking Christmas lights. It is thought that up to 10 percent of all people experience a seizure sometime in life. In children, for instance, seizures are frequently the result of a high fever. Seizures may also be triggered by a blow to the head or inadequate blood flow to the brain due to heart disease.

The umbrella term epilepsy, however, refers to a disorder that causes multiple seizures. Some people appear to be born with a tendency toward the disease; others acquire it later because of physical damage to the brain. For instance, about 25 percent of people who sustain brain damage during a stroke develop epilepsy. People who suffer a head injury in a car accident or who undergo brain surgery may also experience repeated seizures. The abnormal electrical activity can occur throughout the entire brain (a generalized seizure) or in one particular area (a partial, or "focal," seizure).

During a seizure, the normal functioning of the brain is disrupted. This is why people often report "blacking out," meaning they have no memory of the event. This reflects a disruption in the brain circuits that form and store memories. Neurologists even have a name for it: Transient Epileptic Amnesia (TEA).

Anticonvulsants, the drugs used to treat epilepsy, reduce the severity and frequency of seizures, but they can also impair normal brain functions and cause memory problems. The reasons why are not totally clear. It may be that at high doses, the medications slow the brain down so much that the patient has trouble learning and remembering new information. Usually doctors can solve this problem by finding just the right medication and dose for the patient.

Temporal Lobe Epilepsy

Having a single seizure, or even several seizures, will probably not cause permanent damage. The most serious and persistent memory loss happens to people who have experienced many seizures. The repeated storms of electrical activity leave brain cells scarred and disabled, like light bulbs that have burned out from excessive use. The focus of the seizures is often in a brain region important to memory: the temporal lobes.

When the temporal lobes are damaged, people often begin to have trouble forming new memories. This type of memory deficit, known as anterograde amnesia, is one of the hallmarks of temporal lobe epilepsy. A man with anterograde amnesia might, for example, fail to recognize someone he met yesterday or have trouble remembering conversations that took place a few hours ago.

The memory loss in temporal lobe epilepsy can show itself in subtle ways, explains Teresa Blaxton, Ph.D., an associate professor of psychiatry at the University of Maryland School of Medicine in Baltimore. In studies conducted at the National Institutes of Health (NIH) in Bethesda, Maryland, Blaxton and her colleagues discovered that seizures in the left temporal lobe can impair the ability to pick up on concepts hidden in certain kinds of information, such as the categories that a list of items might be sorted by.

Blaxton's studies involved people with a long history of seizures in either their left or right temporal lobes. The test subjects listened to lists of words that contained items from a number of categories-for example, "hat, coat, dog, cat, shoes, horse, chicken," and so on. Normally, people recognize the hidden categories-clothes and animals in this example-and this helps them to remember the information and recall it later.

However, in Blaxton's studies, people with left temporal lobe epilepsy had a hard time picking up on the categories, even after listening to the list several times. Even when all the words from a single category were clustered together in the list-a change that should make the categories more obvious-the people with damage to the left temporal lobe did not improve on the test. The people with damage to the right lobes did improve, as did a group of people without epilepsy who were tested for comparison.

This finding makes sense, given that the left temporal lobe is an important location for language processing. This leads to impairments in what is usually referred to as "verbal memory." Jeffrey Ojemann, MD, a neurosurgeon at the Washington University School of Medicine in St. Louis, sees this impairment in many of his patients with left-temporal lobe epilepsy. The result is difficulty with ordinary tasks such as reading a newspaper or holding a conversation. Ojemann thinks this may be because by the time the patients reach the middle of the article or conversation, they may have forgotten much of the beginning.

In contrast, people with seizures in the right temporal lobe don't usually have these verbal memory problems, Ojemann says. Instead, they show slight impairments in a skill known as spatial memory, which includes the memory for locations in space (for example, the location of a friend's house). However, Ojemann emphasizes, the spatial memory problems can be detected only during certain neuropsychological tests-not in situations we normally encounter every day. Thus, for a person with epilepsy, seizures in the right temporal lobe are often less of a problem in day-to-day life than seizures in the left temporal lobe, which affect the language comprehension skills we use in myriad ways every day.

From Theory to Therapy

Basic research on the ways that epilepsy affects different parts of the brain-in this case, left versus right temporal lobe-can actually benefit patients. It might, for example, make it possible to tailor rehabilitation programs to the particular memory impairment a person is experiencing. That might suggest strategies for overcoming the impairment, perhaps by training people to rely more on intact memory skills. And that could make the aftermath of storms in the brain just a little easier to weather.  

Further Reading:

"Memory and intelligence in lateralized temporal lobe epilepsy and schizophrenia," by J. Gold, T. Blaxton and others. Schizophrenia Research, vol 17, pp. 59-65.

"Learning impairment in epileptic patients," by P. Loiseau and others. Epilepsia, vol. 24, pp. 182-192.

"Transient epileptic amnesia: a description of the clinical and neuropsychological features in 10 cases and a review of the literature," by A. Zeman and others. Journal of Neurology, Neurosurgery and Psychiatry, vol. 64, pp. 435-443.

The Epilepsy Foundation offers a range of information and services for people with epilepsy. They can also point you to local affiliates of the foundation. Contact them at:

The Epilepsy Foundation
4351 Garden City Drive,
Landover, MD 20785
(800) 332-1000
(301) 459-3700
http://www.efa.org


 
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