Amnesia

Amnesia 

Definition

Amnesia refers to the loss of memory. Memory loss may result from two-sided (bilateral) damage to parts of the brain vital for memory storage, processing, or recall (the limbic system, including the hippocampus in the medial temporal lobe).

Description

Amnesia can be a symptom of several neurodegenerative diseases; however, people whose primary symptom is memory loss (amnesiacs), typically remain lucid and retain their sense of self. They may even be aware that they suffer from a memory disorder.

People who experience amnesia have been instrumental in helping brain researchers determine how the brain processes memory. Until the early 1970s, researchers viewed memory as a single entity. Memory of new experiences, motor skills, past events, and previous conditioning were grouped together in one system that relied on a specific area of the brain.

If all memory were stored in the same way, it would be reasonable to deduce that damage to the specific brain area would cause complete memory loss. However, studies of amnesiacs counter that theory. Such research demonstrates that the brain has multiple systems for processing, storing, and drawing on memory.

Causes and symptoms

Amnesia has several root causes. Most are traceable to brain injury related to physical trauma, disease, infection, drug and alcohol abuse, or reduced blood flow to the brain (vascular insufficiency). In Wernicke-Korsakoff syndrome, for example, damage to the memory centers of the brain results from the use of alcohol or malnutrition. Infections that damage brain tissue, including encephalitis and herpes, can also cause amnesia. If the amnesia is thought to be of psychological origin, it is termed psychogenic.

Memory loss may result from bilateral damage to the limbic system of the brain responsible for memory storage, processing, and recall.

(Illustration by Electronic Illustrators Group).

There are at least three general types of amnesia:

Diagnosis

In diagnosing amnesia and its cause, doctors look at several factors. During a physical examination, the doctor inquires about recent traumas or illnesses, drug and medication history, and checks the patient's general health. Psychological exams may be ordered to determine the extent of amnesia and the memory system affected. The doctor may also order imaging tests such as magnetic resonance imaging (MRI) to reveal whether the brain has been damaged, and blood work to exclude treatable metabolic causes or chemical imbalances.

Treatment

Treatment depends on the root cause of amnesia and is handled on an individual basis. Regardless of cause, cognitive rehabilitation may be helpful in learning strategies to cope with memory impairment.

Prognosis

Some types of amnesia, such as transient global amnesia, are completely resolved and there is no permanent loss of memory. Others, such as Korsakoff syndrome, associated with prolonged alcohol abuse or amnesias caused by severe brain injury, may be permanent. Depending on the degree of amnesia and its cause, victims may be able to lead relatively normal lives. Amnesiacs can learn through therapy to rely on other memory systems to compensate for what is lost.

Prevention

Amnesia is only preventable in so far as brain injury can be prevented or minimized. Common sense approaches include wearing a helmet when bicycling or participating in potentially dangerous sports, using automobile seat belts, and avoiding excessive alcohol or drug use. Brain infections should be treated swiftly and aggressively to minimize the damage due to swelling. Victims of strokes, brain aneurysms, and transient ischemic attacks should seek immediate medical treatment.

Resources

Periodicals

Squire, Larry R., and Stuart M. Zola. "Amnesia, Memory and Brain Systems." Philosophical Transactions of the Royal Society of London, Series B 352 (1997): 1663.

Key terms

Classical conditioning — The memory system that links perceptual information to the proper motor response. For example, Ivan Pavlov conditioned a dog to salivate when a bell was rung.

Emotional conditioning — The memory system that links perceptual information to an emotional response. For example, spotting a friend in a crowd causes a person to feel happy.

Explicit memory — Conscious recall of facts and events that is classified into episodic memory (involves time and place) and semantic memory (does not involve time and place). For example, an amnesiac may remember he has a wife (semantic memory), but cannot recall his last conversation with her (episodic memory).

Limbic system — The brain structures involved in memory.

Magnetic resonance imaging (MRI) — MRI uses a large circular magnet and radio waves to generate signals from atoms in the body. These signals are used to construct images of internal structures.

Motor skill learning — This memory system is associated with physical movement and activity. For example, learning to swim is initially difficult, but once an efficient stroke is learned, it requires little conscious effort.

Neurodegenerative disease — A disease in which the nervous system progressively and irreversibly deteriorates.

Priming memory — The memory system that joins perceptual and conceptual representations.

Transient ischemic attack — A sudden and brief blockage of blood flow in the brain.

Working memory — The memory system that relates to the task at hand and coordinates recall of memories necessary to complete it.

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amnesia /am·ne·sia/ (am-ne´zhah) pathologic impairment of memory.

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anterograde amnesia  amnesia for events occurring subsequent to the episode precipitating the disorder.

dissociative amnesia  a dissociative disorder characterized by a sudden loss of memory for important personal information and which is not due to the direct effects of a psychogenic substance or a general medical condition.

psychogenic amnesia  dissociative a.

retrograde amnesia  amnesia for events occurring prior to the episode precipitating the disorder.

transient global amnesia  a temporary episode of short-term memory loss without other neurological impairment.

visual amnesia  alexia.

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am·ne·sia (m-nzh)

n.

The loss or impairment of memory.

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amnesia,

n memory loss; may be due to brain trauma, acute emotional distress, stroke, or other causes.

amnesia, sensorimotor,

n concept explored in the Feldenkrais method in which students lie on the floor and scan their own bodies, discovering disconnections in terms of kinesthetic linking. See also method, Feldenkrais.

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amnesia (amnē´zē, -zh),

n the lack or loss of memory.

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amnesia Neurology A pathologic impairment or lack of memory, which is often temporally linked to a traumatic event Types Anterograde–no memory for that occurring after the event; retrograde–no memory for that occurring before the event; amnesia may be organic, emotional, mixed origin, or time-limited. See Anterograde amnesia, Hysterical amnesia, Retrograde amnesia, Selective amnesia, Sensorimotor amnesia, Source amnesia.