In general, amnestic disorders are caused by structural or chemical damage to parts of the brain. Problems remembering previously learned information vary widely according to the location and the severity of brain damage. The ability to learn and remember new information, however, is always affected in an amnestic disorder.
Amnestic disorder due to a general medical condition can be caused by head trauma, tumors, stroke, or cerebrovascular disease (disease affecting the blood vessels in the brain). Substance-induced amnestic disorder can be caused by alcoholism, long-term heavy drug use, or exposure to such toxins as lead, mercury, carbon monoxide, and certain insecticides. In cases of amnestic disorder caused by alcoholism, it is thought that the root of the disorder is a vitamin deficiency that is commonly associated with alcoholism, known as Korsakoff's syndrome. The causes of transient global amnesia, or TGA, are unclear.
In addition to problems with information recall and the formation of new memories, people with amnestic disorders are often disoriented with respect to time and space, which means that they are unable to tell an examiner where they are or what day of the week it is. Most patients with amnestic disorders lack insight into their loss of memory, which means that they will deny that there is anything wrong with their memory in spite of evidence to the contrary. Others will admit that they have a memory problem but have no apparent emotional reaction to their condition. Some persons with amnestic disorders undergo a personality change; they may appear apathetic or bland, as if the distinctive features of their personality have been washed out of them.
Some people experiencing amnestic disorders confabulate, which means that they fill in memory gaps with false information that they believe to be true. Confabulation should not be confused with intentional lying. It is much more common in patients with temporary amnestic disorders than it is in people with long-term amnestic disorders.
Transient global amnesia (TGA) is characterized by episodes during which the patient is unable to create new memories or learn new information, and sometimes is unable to recall past memories. The episodes occur suddenly and are generally short. Patients with TGA often appear confused or bewildered.
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