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Biology 202, Spring 2005 First Web Papers On Serendip

The Impact of Epilepsy on Memory

Camilla Culler

Epilepsy is an enigma in many ways because scientists and clinicians are still searching for answers regarding causation, treatment, and how to differentiate it from other seizure disorders. Because of the unanswered questions concerning the disease, many people living with the disease are fearful of seizures, for the onset is abrupt and it can strike at any moment. My best friend from high school who was diagnosed with the disease at age 18 recently related to me an occurrence that had happened during one of her seizures. She was sitting in her room studying and all of a sudden she began to have a seizure with convulsions. Her roommate immediately called an ambulance. However, it appears that during the seizure my friend Liz got up from the floor and went to the door to greet the EMS workers. She then collapsed onto her bed. Interestingly, she had no memory of greeting the workers at the door and she only was aware that this event took place because her roommate told her later on. In fact she had no memory of the seizure at all, which is apparently the normal response for an epileptic post seizure. My friend Liz has primary generalized epilepsy, which means that when a seizure occurs the whole brain is impacted rather than a specific localized area (5). After hearing about this incident I was concerned about the affect that epilepsy has on memory. I was left wondering how the seizure itself can impact memory, which parts of the brain correspond to which types of memory, and why it is the case that Liz does not remember greeting the EMS workers?

An epileptic is defined as a person who has experienced multiple seizures and all other possible reasons for the onset of a seizure- besides origination in the brain- such as high fever or injury, have been ruled out. The seizure occurs when the chemical message being sent from the axon of a single neuron to the dendrite of a fellow neuron gets excited and the excitation overwhelms the inhibition. This chemical exchange happens on a grand scale in the epileptic brain. As we learned in class once an action potential is reached there is no turning back. Thus the neurological impulses are firing out of control with no inhibitory influences to counteract them (5). As a result of the firing the epileptic loses control, and they can experience severe convulsions, during which the person is not aware of their surroundings (1). When Liz got up to greet the workers she was in a cognitive state where her brain was unable to learn and acquire new knowledge of her surroundings. She was thus unaware, and in a temporary state of "post-ictal confusion" (1). Since the epileptic cannot describe the seizure incident clearly, because they have no memory of it, I can imagine that it is difficult for physicians to fully understand the patient's experience while the seizure is occurring. The only thing physicians can do is observe the behaviors of the patient and measure brain activity on an EEG. Thus the picture of epilepsy remains incomplete.

Besides being physically dangerous, (a person can hit their head or bang into something), seizures can also cause neurocognitive damage. An especially long series of convulsions or multiple seizures all at once are more dangerous to the brain than a single short episode, because brain damage is more likely (1). The term status epilepticus refers to repeated generalized seizures without return to consciousness between the events. Depending on which part of the brain the seizure affects, this will determine the type and extent of the damage if any that will take place. One region of the brain that has been found to be especially vulnerable to repeated seizures is the hippocampus. (6) The hippocampus is a region of the cerebral cortex located in the temporal lobe and is involved in learning and memory. The hippocampus plays a key role in allowing new information to be imputed in the brain's memory storage systems (3). The excitatory neurotransmitter, glutamate, and the excessive stimulation of glutamate receptors may be responsible for the neuronal damage in the hippocampus. This phenomenon has been referred to as excitotoxicity (6).

Liz reported problems recalling tasks that she needed to accomplish the next day that she had planned to do the day before her seizure. She had planned to go to the gym with two of her friends and when she didn't remember to show up they became alarmed. This forgetfulness of future events may have been due to slight damage sustained in the frontal lobe, which is responsible for recalling upcoming events and plans. It might also be due to the fact that she takes AEDs (anti-epileptic medications), which can affect your short-term memory. Other areas of the brain such as the temporal lobe affect learning, whereas long-term memory is distributed throughout the brain (4).

Besides her inability to remember to go to the gym, Liz described her feelings post seizure as being "foggy" and "confused". She took a lot of naps and felt like she couldn't concentrate on her homework. After a few days the feelings faded but they kept her out of commission for a while. Whether these feelings of fogginess were due to the seizure itself or the AEDs is questionable. Since AEDs can often cause you to feel tired and effect your capacity to learn (1), increasing the dosage after a seizure in order to limit the chances of another one occurring, will generally make the patient more susceptible to these side effects.

Interestingly, pre-seizure the feeling of fogginess was also present but in a more pleasant way. Described as a feeling of "Deja vu " or a "gratulant" feeling, a generalized euphoria or experience of altered consciousness can come over a person before they begin seizing (4). Experiencing an "aura" is another indicator of the onset of a seizure (2). The aura or fuzzy feeling is due to the onset of excessive firing of neurons in the brain (4). However, some people experience nothing unusual before a seizure and thus have no indication that they are going to have one.

After hearing my friend's account of her seizure and reading about the causes and effects the disease has on memory it seems that the main causes of memory disturbances are brain damage from the seizure itself, the side effects of the AEDs, the after effects of the seizure or "fogginess", and the"post-ictal" confusion experienced during the seizure. I am still left with the unanswered questions of why some patients experience the feeling of an "aura" while others don't, and how Elizabeth was physically able to get up and go to the door during a seizure. There are many aspects of epilepsy that are still not completely understood, which is the reason why more research is needed in this field. In order to pioneer a cure we must first have a more complete understanding of the disease itself.

References

1)National Society For Epilepsy, info on the disease, causation, and treatment
2)The Brain Matters, From the Serendip website list.
3) Bear, Mark F., Connors, Barry Q., and Paradiso, Michael A. Neuroscience Exploring The Brain (2nd ed.). Baltimore: Lippincott Williams & Wilkins, 2001.
4) Gellatly, Angus and Zarate, Oscar. Introducing Mind And Brain. New York: Totem Books, 1999.
5) Gumnit, Robert J. (2004). Neither Gods nor Demons But Misfiring Brains. Cerebrum, Vol 6, number 2, 27-40.
6) Jessell, Thomas M., Kandel, Eric R., and Schwartz, James H. (ed.). Principles of Neural Science (4th ed.). New York: McGraw-Hill, 2000.



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