From Wikipedia, the free encyclopedia
Amnesia (from Greek Ἀμνησία) is a memory condition in which memory is disturbed. In simple terms, it is the loss of memory. The causes of amnesia are organic or functional. 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. Hysterical post-traumatic amnesia is an example of this. Amnesia may also be spontaneous, in the case of transient global amnesia. This global type of amnesia is more common in middle-aged to elderly people, particularly males, and usually lasts less than 24 hours.
Another effect of amnesia is the inability to imagine the future. A 2006 study published online in the Proceedings of the National Academy of Sciences shows that amnesiacs with damaged hippocampus cannot imagine the future. This is because a normal human being, imagining the future, uses past experiences to construct a possible scenario. For example, a person trying to imagine what would happen at a party set to occur in the near future would use past experience at parties to help construct the event.
Forms of amnesia
- In anterograde amnesia, new events contained in the immediate memory are not transferred to the permanent as long-term memory.
- Retrograde amnesia is the distinct inability to recall some memory or memories of the past, beyond ordinary forgetfulness.
The 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 over the next two days (anterograde amnesia).
The effects of amnesia can last long after the condition has passed; many sufferers claim that amnesia changes from a neurological condition to a psychological condition, whereby the patient loses confidence and faith in their own memory and accounts of past events.
Types and causes of amnesia
Post-traumatic amnesia is generally due to a head injury (e.g. a fall, a knock on the head). Traumatic amnesia is often transient, but may be permanent of either anterograde, retrograde, or mixed type. The extent of the period covered by the amnesia is related to the degree 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 lose knowledge of who people are, they may remember events, but will not remember faces of them.
- Dissociative amnesia results from a psychological cause as opposed to direct damage to the brain caused by head injury, physical trauma or disease, which is known as organic amnesia. Dissociative amnesia can include:
- 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 e.g. anterograde amnesia caused by amnestics such as benzodiazepines or alcohol, where an experience was prevented from being transferred from temporary to permanent memory storage: it will never be recovered, because it was never stored in the first place. Formerly known as "Psychogenic Amnesia".
- 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."  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.
- Childhood amnesia (also known as infantile amnesia) is the common inability to remember events from one's own childhood. Sigmund Freud attributed this to sexual repression, while 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.
- 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.
- Drug-induced amnesia is intentionally caused by injection of an amnesiac drug to help a patient forget surgery or medical procedures, particularly those which are not performed under full anesthesia, or which are likely to be particularly traumatic. Such drugs are also referred to as "premedicants". Most commonly a 2'-halogenated benzodiazepine such as midazolam or flunitrazepam is the drug of choice, although other strongly amnestic drugs such as propofol or scopolamine may also be used for this application. Memories of the short time frame in which the procedure was performed are permanently lost or at least substantially reduced, but once the drug wears off, memory is no longer affected.
- Prosopamnesia is the inability to remember faces, even in the presence of intact facial recognition capabilities. Both acquired and inborn cases have been documented.
- Situation-Specific amnesia can arise in a variety of circumstances (e.g., committing an offence, child sexual abuse) resulting in PTSD. It has been claimed that it involves a narrowing of consciousness with attention focused on central perceptual details and/or that the emotional or traumatic events are processed differently from ordinary memories.
In popular culture
Global amnesia is a common motif in fiction despite being extraordinarily rare in reality. In the introduction to his anthology The Vintage Book of Amnesia, Jonathan Lethem writes:
Real, diagnosable amnesia – people getting knocked on the head and forgetting their names – is mostly just a rumor in the world. It's a rare condition, and usually a brief one. In books and movie, though, versions of amnesia lurk everywhere, from episodes of Mission Impossible to metafictional and absurdist masterpieces, with dozens of stops in between. Amnesiacs might not much exist, but amnesiac characters stumble everywhere through comic books, movies, and our dreams. We've all met them and been them.
Lethem traces the roots of literary amnesia to Franz Kafka and Samuel Beckett, among others, fueled in large part by the seeping into popular culture of the work of Sigmund Freud, which also strongly influenced genre films such as film noir. Amnesia is so often used as a plot device in films, that a widely-recognized stereotypical dialogue has even developed around it, with the victim melodramatically asking "Where am I? Who am I? What am I?", or sometimes inquiring of his own name, "Bill? Who's Bill?"
In movies and television, particularly sitcoms and soap operas, it is often depicted that a second blow to the head, similar to the first one which caused the amnesia, will then cure it. 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.
Amnesia has also been useful as a plot device in many video games, to help explain why the main character, and therefore the player, knows very little about the world he is in. "Amnesia" has also been used as the title for a number of songs, including those by Britney Spears and the progressive death metal band In Mourning.
|Mental and behavioral disorders (F · 290–319)|
(acute alcohol intoxication
, alcohol dependence
, alcoholic hallucinosis
, Alcohol withdrawal
, delirium tremens
, Korsakoff's syndrome
, alcohol abuse
) · opioids
, opioid dependency
) · sedative/hypnotic
, benzodiazepine dependence
, benzodiazepine withdrawal
) · cocaine
, cocaine dependence
) · general
, Physical dependence
, Rebound effect
diagnosed in childhood
|psychology navs: mental processes, disorders, symptoms/signs, speech/voice, psychotherapy|
|Symptoms and signs: cognition, perception, emotional state and behaviour (R40-R46, 780.0-780.5,781.1)|
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