Anterograde amnesia

Overview
Anterograde amnesia is a form of amnesia, or memory loss, in which new events are not transferred from short-term memory to long-term memory. This may be a permanent deficit, or it may be temporary, such as is sometimes seen for a period of hours or days after head trauma or for a period of intoxication with an amnestic drug. The deficit makes its sufferers unable to recall an event which occurred only moments earlier when their attention has shifted to something else.

Symptoms
Those who have theoretically pure anterograde amnesia are still able to access memories formed before its onset, but they exist in a transient world where anything beyond their immediate attention span disappears from their consciousness permanently. However, theoretically pure anterograde amnesia rarely surfaces: in reality, long-term cases nearly always occur with some degree of retrograde amnesia.

Anterograde amnesia is often informally, but incorrectly, called "short-term memory loss", conjuring up the idea, as in the movie Memento, that it is a problem of short-term memory. For this reason, formal (correct technical or scientific) usage demands the term anterograde amnesia, since the deficit is not in short-term memory, but rather in encoding into more permanent, long-term memory.

Anterograde amnesiacs suffer differing degrees of impairment to different types of memories. Patients can often learn and remember how to do a new physical skill (e.g., playing the guitar, learning the words to a new song and then singing them, etc.) but not remember when they learned it. Such "how-to", motor skill learning (procedural memory) and its attendant behavioural conditioning and priming are collectively known as non-declarative memory, which appears to be unaffected by anterograde amnesia.

However, the condition tends to impair both episodic memory (the memory of events) and semantic memory (the memory of facts and general knowledge). For the most part, patients are unable to make new semantic or episodic memories. Yet the research at this time conflicts enough that consensus on this point has not been reached: some patients appear able to create new semantic memories, and young children with anterograde amnesia seem to have semantic learning capabilities similar to non-amnesiacs.

Causes
Anterograde amnesia can result from damage to the hippocampus, fornix, or mammillary bodies, thus lending credence to the theory that these structures are primarily responsible for laying down long-term memories. However, the condition can also arise from damage to the basal forebrain (which produces acetylcholine) or a set of brain structures called the diencephalon.

"Traveler's amnesia" is a temporary form of anterograde amnesia in which victims may, for instance, realise they have changed planes during a memory gap or discover that they rented a car. This condition is caused by some medications, notably imidazopyridines and benzodiazepines, especially when they are used as sleep aids. Although medical researchers characterize this side effect as "less common",, the benzodiazepine triazolam (Halcion) apparently has the greatest chance of inducing traveler's amnesia, whether taken exactly as directed, varying the dosage (say, when coming off the drug too quickly), drinking alcohol, or not getting enough sleep. However, benzodiazepines alprazolam (Xanax) and nitrazepam (Mogadon) are also more likely to be at fault, the former on its own and the latter when the victim is sleep-deprived or in some way changing the dose.

Criminals may use medications with anterograde amnesic effects for date rape. Unbeknownst to the victim, the perpetrator uses drugs such as flunitrazepam, temazepam, and other common substances, usually in a drink, to cause disorientation; incapacitation; unconsciousness; distortions in vision, time, sense, and identity; and an uninhibited state, the hallmark of which is anterograde amnesia.

Amnesia automatism is usually induced by prescription drugs, frequently but not necessarily in association with moderate alcohol intake. Victims have memory gaps for a period shortly after taking the drug concerned, which causes embarrassment and fear for what might have happened. Disinhibited and uncharacteristic behaviour (sometimes together with carrying out quite complex tasks - e.g. cooking and serving a nice meal, but in the nude) is sometimes witnessed during such episodes, which adds further embarrassment and distress.

Famous cases
The most famous case of anterograde amnesia is that of HM or Henry M. His brain lesions accidentally started the inquiry into the neurobiology of learning and memory.

Another notable patient is Clive Wearing, who was featured in the documentary The Man with the 7 Second Memory. Wearing fell ill with a variety of herpes simplex virus. The virus attacked his brain, doing greatest damage to the hippocampus, which is crucial for handling memory.

Oliver Sacks writes on two men with anterograde amnesia in two chapters of his book The Man Who Mistook His Wife for a Hat. Both suffer from Korsakoff's syndrome, which causes an anterograde amnesia that is irreversible. "The Lost Mariner" chronicles the life of a patient who, since he has forgotten everything that has happened since World War II, lives in complete certainty that it is 1945. Oblivious to his condition, he also believes he is decades younger. In "A Matter of Identity", Sacks profiles the other man, also unaware he suffers from amnesia. Rather than having a consistent false belief about his situation, he deals with his amnesia by constantly re-evaluating and re-explaining his situation. For instance, he greets whoever is with him in the room over and over again, each time with a different name.

Anterograde amnesia in fiction

 * The 1940 satire The Great Dictator featured a Jewish barber who suffered from anterograde amnesia, thinking it to be just after the end of WWI, though he recovered early in the film.
 * The 1985 short story A Clean Escape by John Kessel, in which a psychiatrist torments a man suffering from Korsakoff's syndrome. It was adapted into an audio drama for Sci Fi Channel's Seeing Ear Theatre. . This was adapted to TV in Masters of Science Fiction pilot-episode "A Clean Escape"
 * Several episodes of Saturday Night Live featured Tom Hanks starring in the recurring sketch "Mr. Short Term Memory", where his character would almost immediately forget what he was doing or talking about, to humorous effect.
 * In the 1994 comedy Clean Slate, Dana Carvey stars as a man whose anterograde amnesia kicks in whenever he falls asleep (typically once a day).
 * The 2000 neo-noir/psychological thriller film Memento, starring Guy Pearce, Carrie-Anne Moss, and Joe Pantoliano, featured Leonard (played by Pearce), a man who developed anterograde amnesia after suffering a severe head injury. Leonard seems to be a pure anterograde amnesiac who remembers the details of his earlier life but is unable to form new memories. However, he is aware that he suffers from anterograde amnesia because he had researched the condition before his own injury as part of his job as an insurance claim investigator. The story is told in reverse chronology divided into episodic sections. Between each section, a portion of the first chronological scene is shown. The two narrations converge in the end. This provides the viewer with a kind of 'simulation' as to what anterograde amnesia might be like, as the viewer watches each new scene without knowing what events preceded it.
 * The 2003 animated comedy Finding Nemo features the voice of Ellen DeGeneres as Dory, a regal blue-tang fish with anterograde amnesia. For example, she invites Marlin to accompany her, then forgets meeting him and becomes upset when she concludes that he is stalking her.
 * The November 5, 2003 episode "Twilight" of science fiction TV series Star Trek: Enterprise opens with Captain Archer (Scott Bakula) having unknowingly suffered from anterograde amnesia for 12 years.
 * The 2004 romantic comedy 50 First Dates casts Adam Sandler as a man who must start anew every day his wooing of anterograde sufferer Drew Barrymore. In the film the disease is called Goldfield's syndrome.
 * In the 1965 film 36 Hours starring James Garner and Eva Marie Saint, Garner stars as a military planner kidnapped on the eve of the WWII Normandy invasion, and induced to believe he has amnesia in order to reveal the invasion plan.
 * The Vintage Book of Amnesia: An Anthology of Writing on the Subject of Memory Loss, edited by Jonathan Lethem, contains a wide variety of fiction and non-fiction, some of which explores anterograde amnesia.
 * In Kingdom Hearts II, Oogie Boogie develops anterograde amnesia after being brought back from the dead by Maleficent. He forgot who brought him back to life after a few cutscenes, and forgets who Santa Claus is and why he kidnapped him despite being ordered by Maleficent to do so.
 * In the book A Fire Upon the Deep by Vernor Vinge, an entire alien species known as the Skroderiders has no short term memory. These plant-creatures depend on their Skrodes to mobilize them and to aid them in putting things into their long term memory. There are several instances where the reader is treated to scenes of Humans trying to hold conversations with them, with varying degrees of success.
 * In the novel Mona Lisa Overdrive by William Gibson, the character Slick Henry has several stress-related relapses of chemically induced Korsakoff's Syndrome, previously used on him as an institutional punishment for Grand Theft Auto.
 * In Rumbling Hearts (otherwise known as Kimi Ga Nozomu Eien) the character Haruka suffers from anterograde amnesia.