amnesia

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amnesia

(ămnē`zhə), [Gr.,=forgetfulness], condition characterized by loss of memorymemory,
in psychology, the storing of learned information, and the ability to recall that which has been stored. It has been hypothesized that three processes occur in remembering: perception and registering of a stimulus; temporary maintenance of the perception, or short-term
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 for long or short intervals of time. It may be caused by injury, shock, senility, severe illness, or mental disease. Some cases of amnesia involve the unconscious suppression of a painful experience and everything remindful of it including the individual's identity (see defense mechanismdefense mechanism,
in psychoanalysis, any of a variety of unconscious personality reactions which the ego uses to protect the conscious mind from threatening feelings and perceptions.
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). Retrograde amnesia is loss of memory of events just preceding temporary loss of consciousness, as from head injury; it is evidence that memory proceeds in two stages, short term and long term. One form of the condition known as tropic amnesia, or coast memory, affecting white men in the tropics, is probably a variety of hysteriahysteria
, in psychology, a disorder commonly known today as conversion disorder, in which a psychological conflict is converted into a bodily disturbance. It is distinguished from hypochondria by the fact that its sufferers do not generally confuse their condition with real,
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. Aphasiaaphasia
, language disturbance caused by a lesion of the brain, making an individual partially or totally impaired in his ability to speak, write, or comprehend the meaning of spoken or written words.
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 of the amnesic variety is caused by an organic brain condition and is not to be confused with other forms of amnesia. To cure amnesia, attempts are made to establish associationsassociation,
in psychology, a connection between different sensations, feelings, or ideas by virtue of their previous occurrence together in experience. The concept of association entered contemporary psychology through the empiricist philosophers John Locke, George Berkeley,
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 with the past by suggestion, and hypnotismhypnotism
[Gr.,=putting to sleep], to induce an altered state of consciousness characterized by deep relaxation and heightened suggestibility. The term was originally coined by James Braid in 1842 to describe a phenomenon previously known as animal magnetism or mesmerism (see
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 is sometimes employed.

Amnesia

A significant but relatively selective inability to remember. Amnesia can be characterized along two dimensions with respect to its onset: an inability to remember events that occurred after the onset of amnesia is referred to as anterograde amnesia, and a deficit in remembering events that occurred prior to the onset of amnesia is referred to as retrograde amnesia. Amnesia can be due to a variety of causes and can be classified according to whether the cause is primarily neurological or psychological in origin. Neurological amnesias are the result of brain dysfunction and can be transient or permanent. They are usually characterized by a severe anterograde amnesia and a relatively less severe retrograde amnesia. Transient amnesias are temporary memory disturbances and can range in duration from hours to months, depending on the cause and severity. They can be caused by epilepsy, head injury, and electroconvulsive therapy (most frequently used for the treatment of depression). In cases of transient global amnesia, an extensive amnesia that is usually sudden in onset and resolves within a day, the cause is still not known, although many believe that it is vascular in origin.

Permanent amnesia usually occurs following brain damage to either the diencephalons or the medial temporal lobe. Amnesia resulting from impairment to the medial temporal lobe can occur following anoxia, cerebrovascular accidents, head injury, and viral infections to the brain. The primary structures involved in the processing of memory within the medial temporal lobe are the hippocampus and the amygdala. One of the most common causes of diencephalic amnesia is Wernicke-Korsakoff syndrome, a disorder caused by a thiamine deficiency, usually related to chronic alcoholism.

Memory impairment that is not associated with brain damage is referred to as functional amnesia. Functional amnesia can be classified according to whether the amnesia is nonpathological or pathological. Nonpathological functional amnesia is a normal memory loss for events occurring during infancy and early childhood, sleep, hypnosis, and anesthesia. Pathological functional amnesia is an abnormal memory loss found in cases of functional retrograde amnesia and multiple personality. In contrast to neurological amnesia, pathological functional amnesia is usually associated with more severe retrograde than anterograde amnesia. See Brain, Memory

amnesia

[am′nēzh·ə]
(medicine)
The pathological loss or impairment of memory brought about by psychogenic or physiological disturbances.

amnesia

a defect in memory, esp one resulting from pathological cause, such as brain damage or hysteria