Amnesia refers to loss of memories, usually subsequent to some type of neurological event. The loss can be in terms of recent or distant past memories or may involve the loss of ability to form new memories.
The condition called amnesia may have either functional or organic etiology. Functional amnesia is typically caused by extreme emotional or psychological trauma. The event(s) are so overwhelming or threatening to recall that the individual pushes memories out of consciousness and renders them inaccessible. This form of amnesia is relatively uncommon. Some of the most often-cited causes of functional amnesia are: being the victim or witness to a violent crime; combat experiences; being witness or victim to terrorist acts; experiencing a natural disaster such as a tornado or tsunami; and being the victim or witness to domestic violence, child abuse, or sexual crime.
There are numerous causes of functional organic amnesia, having to do with injuries to the portions of the brain most critical for memory formation. These causes include stroke, injury to the brain, central nervous system (CNS) disease, tumors of the brain or CNS, surgery, alcoholism, long-term substance abuse, encephalitis, and electroconvulsive therapy. Contrary to the popular notion of amnesia in which a person experiences a severe head trauma and is unable to recall who or where he is or anything about the circumstances of his life, the primary symptoms of amnesia are the loss of specific types of memories and/or an inability to learn new information or to form new memories, starting from the onset of the amnesia. Amnesia can be transient (temporary) or permanent.
There are two types of amnesia: retrograde and anterograde. Retrograde amnesia refers to significantly impaired memory of past events or previously highly familiar information. Anterograde amnesia refers to a significantly impaired ability to learn and retain new information, beginning with the onset of the amnestic event. In many types of head trauma, memories of recent events are lost, either temporarily or permanently.
Amnesia, also called amnestic syndrome, does not affect cognitive efficiency. There is typically no loss of innate intelligence or reasoning ability, although there may be significant deficits in ability to recall current events. There is rarely loss of skills involved in activities important for daily life, such as reading, numerical understanding, ability to operate a motor vehicle, and performing occupational or household activities. Amnesia does not generally affect attention span, intelligence, reasoning ability, sense of humor, sense of self, or personality. Most people with amnestic syndrome have awareness of their memory deficit. Research studies on amnesia lend support to the scientific belief that multiple brain areas are involved in memory creation and storage.
Most individuals cannot readily access memories of events occurring in infancy or very early childhood. Anna Freud referred to this as infantile amnesia. The most common explanations for this phenomenon have to do with ability to encode, organize, and later access information stored before the development and acquisition of language, as well as the rapid degree of brain maturation during the first few years of life. The scientific community does not consider this a true form of amnesia.
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American Academy of Clinical Neuropsychiatry, Department of Psychiatry (F6248, MCHC-6), University of Michigan Health System, 1500 E. Medical Center Dr., SPC 5295, Ann Arbor, MI, 48109-5295, (734) 936-8269, Fax: (734) 936-9761, https://www.theaacn.org .