Amnesia

For other uses, see Amnesia (disambiguation).

Amnesia Classification and external resources
ICD-10	R41.3
ICD-9	780.9, 780.93
MeSH	D000647

Amnesia is a medical condition involving the loss of memory. Organic causes include damage to the brain, through trauma or disease, or use of certain (generally sedative) drugs. Functional causes are psychological factors, such as defense mechanisms, an example being Hysterical post-traumatic amnesia. Amnesia may also be spontaneous, in the case of transient global amnesia a condition more common in middle-aged to elderly people, particularly males, that lasts usually less than 24 hours.

Another effect of amnesia is the inability to imagine the future. A recent study published online in the Proceedings of the National Academy of Sciences shows that amnesiacs with a damaged hippocampus cannot imagine the future[1]. This is because when a normal human being imagines the future, they use their past experiences to construct a possible scenario. For example, a person who would try to imagine what would happen at a party that would occur in the near future would use their past experience at parties to help construct the event in the future.

Forms of amnesia

• In anterograde amnesia, new events contained in the immediate memory are not converted into long-term memory. The sufferer will not be able to remember anything of a recently past event.

• Retrograde amnesia is the inability to recall some memory or memories of the past, beyond ordinary forgetfulness.

Both terms are used to categorize patterns of symptoms, rather than to indicate a particular cause or etiology. Both categories of amnesia can occur together in the same patient, and commonly result from drug effects or damage to the brain regions most closely associated with episodic/declarative memory: the medial temporal lobes and especially the hippocampus.

An example of mixed retrograde and anterograde amnesia may be a motorcyclist unable to recall driving his motorbike prior to his head injury (retrograde amnesia), nor can he recall the hospital ward where he is told he had conversations with family for the few days following the accident (anterograde amnesia).

Subclasses/Causes of amnesia

• Post-traumatic amnesia is generally due to a head injury (e.g. a fall, a knock on the head) that is often transient, but may be permanent of either anterograde, retrograde, or mixed type. The extent of memory loss increases with severity of injury and may give an indication of the prognosis for recovery of other functions. Mild trauma, such as a car accident that results in no more than mild whiplash, might cause the occupant of a car to have no memory of the moments just before the accident due to a brief interruption in the short/long-term memory transfer mechanism. The sufferer may also remember events, but will forget who people are and memories of their faces.

• Dissociative Amnesia results from a psychological cause as opposed to direct brain damage, physical trauma, or disease, making it known as an organic form of the condition. Dissociative Amnesia may include several types:

• Repressed memory refers to the inability to recall information, usually about stressful or traumatic events in persons' lives, such as a violent attack or rape. The memory is stored in long term memory, but access to it is impaired because of psychological defense mechanisms. Persons retain the capacity to learn new information and there may be some later partial or complete recovery of memory. This contrasts with anterograde amnesia for example, which is caused by amnestics such as benzodiazepines or alcohol and involves the inability of an experience from being transferred from temporary to permanent memory storage.

• Dissociative Fugue (formerly Psychogenic Fugue) is also known as fugue state. It is caused by psychological trauma and is usually temporary, unresolved and therefore may return. The Merck Manual defines it as "one or more episodes of amnesia in which the inability to recall some or all of one's past and either the loss of one's identity or the formation of a new identity occur with sudden, unexpected, purposeful travel away from home" [2]. While popular in fiction, it is extremely rare.

• Posthypnotic amnesia is where events during hypnosis are forgotten, or where past memories are unable to be recalled.

• Lacunar amnesia is the loss of memory about one specific event.

• Childhood amnesia (also known as infantile amnesia) is the common inability to remember events from one's own childhood. Whilst Sigmund Freud attributed this to sexual repression, others have theorised that this may be due to language development or immature parts of the brain.

• Transient global amnesia is a well-described medical and clinical phenomenon. This form of amnesia is distinct in that abnormalities in the hippocampus can sometimes be visualized using a special form of magnetic resonance imaging of the brain known as diffusion-weighted imaging (DWI). Symptoms typically last for less than a day and there is often no clear precipitating factor nor any other neurological deficits. The cause of this syndrome is not clear, hypotheses include transient reduced blood flow, possible seizure or an atypical type of migraine. Patients are typically amnestic of events more than a few minutes in the past, though immediate recall is usually preserved.

• Source amnesia is a memory disorder in which someone can recall certain information, but they do not know where or how they obtained the information.

• Memory distrust syndrome is a term invented by the psychologist Gisli Gudjonsson to describe a situation where someone is unable to trust their own memory.

• Blackout phenomenon can be caused by excessive short-term alcohol consumption, with the amnesia being of the anterograde type.

• Korsakoff's syndrome can result from long-term alcoholism or malnutrition. It is caused by brain damage due to a Vitamin B1 deficiency and will be progressive if alcohol intake and nutrition pattern are not modified. Other neurological problems are likely to be present in combination with this type of Amnesia. Korsakoff's syndrome is also known to be connected with confabulation.

Amnesia in fiction

Amnesia is prevalent in many works of fiction, such as in author Robert Ludlum's Bourne series, in which the main character Jason Bourne suffers from retrograde amnesia.

Global amnesia is a common motif in fiction despite being extraordinarily rare in reality. In movies and television, particularly sitcoms, it is often depicted that a second hit to the head (similar to the first one) cures the amnesia. In reality, however, repeat concussions may cause cumulative deficits including cognitive problems, and in extremely rare cases may even cause deadly swelling of the brain associated with second-impact syndrome.

Recent research of fictional works from the 20th century shows that, though hardly anyone gets Amnesia in reality, over 2% of all characters in movies, books, short stories and television shows (particularly soap operas) have had Amnesic effects at some point in their lives.^{[citation needed]}

See also

• Betrayal Trauma
• Clive Wearing
• Emotion and memory
• False memory
• HM (patient)
• Mr. Nobody
• Doug Bruce
• KC (patient)

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