Amnesia (from Greek Ἀμνησία) (see spelling differences) is a condition in which memory is disturbed. 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 recent study published online in the Proceedings of the National Academy of Sciences shows that amnesiacs with damaged hippocampi cannot imagine the future. 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.
In anterograde amnesia, new events contained in the immediate memory are not transferred to the permanent as long-term memory. The sufferer will not be able to remember anything that occurs after the onset of this type of amnesia for more than a brief period following the event.
Retrograde amnesia is the 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).
Traumatic amnesia is generally due to a head injury (fall, 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 could result 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.
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. 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 hippocampi can sometimes be visualized using a special form of MRI 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. Global amnesia is a common motif in fiction despite being extraordinarily rare in reality.
In the 1966 motion picture Mr. Buddwing, the protagonist enters a fugue state in response to distress in his marital relationship.
In the 2004 film The Forgotten, adults struggle with memory loss about the existence of their children, who have been abducted for alien/government experiments.
In the Marvel Comics series X-Men, Wolverine, one of the main characters, has retrograde amenesia due to brainwashing.
In Season 4 of Smallville, Clark Kent has his memory wiped by a Summerholt patient.
In Destination Moon, a part of Adventures of Tintin, Professor Calculus, for a brief period of time suffers from total amnesia, putting the project in trouble since only he knows how to make moon-rocket.
In Century Fox's animated film, Anastasia (1997), Anya suffers from amnesia as a result of having her head hit when trying to climb on train to escape to Paris with her grandmother as a young girl, and cannot recall the first eight years of her life.
The American sitcom Samantha Who? (2007- ) begins with the main character having suffered retrograde amnesia as the result of an auto accident and the show revolves around events that made her remember her life before the accident.
Dissociative Amnesia plays a critical role in the novel Mysterious Skin and movie of the same name.
Author Gene Wolfe addresses amnesia in the series Soldier of the Mist, where the main character Latro is injured during battle, causing relatively long term (24 hour) anterograde amnesia.
In Japanese anime, amnesia is a common theme:
The Big O is largely based on the premise of an entire city having lost their memory forty years prior.
In both Noir and Madlax , the main characters Kirika Yuumura, Madlax and Margaret Burton lose their memory because the memories they had were too traumatic for them.
In Sukisyo, the main characters experienced amnesia because their pasts involve betraying someone dear to them.
In Loveless, the main character has no memories of the first ten or so years of his life and never regains them.
In Utawarerumono the main character has no memory before the series begins. He does not exactly get them back, save for in short bursts, showing several past homicides. These endeavors, with time, become accepted.
In Spirited Away, the character Haku forgot everything about his life as a river spirit, along with his name, which restricted his freedom.
In the award-winning RPG Knights of the Old Republic global amnesia fits prominently into a midgame plot twist.
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, a second concussion would have catastrophic consequences, a phenomenon known as Second Impact Syndrome.