Anterograde amnesia
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Anterograde amnesia is a form of amnesia, or memory loss, where new events are not transferred to long-term memory. After the onset of the disorder, the sufferer will not be able to remember anything that occurs after his attention is shifted away from one subject for more than a few seconds.
Those who suffer from theoretically pure anterograde amnesia will still be able to remember memories laid down before the onset of anterograde amnesia, but will exist in a transient world where anything beyond their immediate attention-span disappears permanently from their consciousness. In reality, anterograde amnesia is nearly always accompanied by some degree of retrograde amnesia.
Damage to the hippocampus, fornix, or mammillary bodies can result in anterograde amnesia, which contributes further evidence to the theory that these are the structures primarily responsible for the process of laying down long-term memories. The occurrence of anterograde amnesia can also be due to damage to the Basal Forebrain which produces acetylcholin. The final cause of anterograde amnesia is damage to a set of structures which are located deep in the brain called the diencephalon
This form of amnesia is often referred to as "short-term memory loss," such as in the movies Memento and Finding Nemo. However, in technical writing anterograde amnesia is used, since the condition is not a deficit in short-term memory but in long-term encoding.
Different types of memories (e.g., of new physical skills, of new words, of the events of the day, facts of history, etc.) can be separately affected by anterograde amnesia. Patients with anterograde memory loss often can learn and remember a new physical skill (e.g., a musician learning how to play a new tune) and yet not remember when he or she had learned it. Examples have been described where patients learned and remembered new words and facts of history ("semantic" memory) but could not remember any events of their previous day ("episodic" memory).
A temporary form of anterograde amnesia, sometimes referred to as traveler's amnesia, is also induced by some medications. Benzodiazepines and imidazopyridines all have varying degrees of anterograde amnesic effects. This is utilised in the use of benzodiazepines such as temazepam and lorazepam as premedicatants. A more sinister, criminal abuse is in date rape (chemical submission), in which the drugs flunitrazepam, GHB, zolpidem, and other common substances are used, unbeknownst to the victim, to produce an uninhibited state, the hallmark of which is anterograde amnesia. Also, unplanned effects of this drug effect are seen in cases of amnesia automatism induced by prescription drugs, often 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. In some cases, victims realise they have changed planes during their memory gap or discover that they rented a car. 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., the man whose lesions accidentally started the inquiry into the neurobiology of learning and memory.Clive Wearing was featured in the documentary, The Man with the 7 Second Memory. Wearing fell ill with a herpes simplex virus which attacked his brain. The affected area was the hippocampus, which has a major role in handling memory.
Oliver Sacks characterizes two individuals with anterograde amnesia in his book The Man Who Mistook His Wife for a Hat. Both suffer from Korsakoff's Syndrome, which causes irreversible anterograde amnesia. The story of one patient is called "The Lost Mariner": he began forgetting everything from the end of WWII and felt certain that the date was constantly 1945. He does not even know that he suffers from amnesia and believes himself to be decades younger than he is. The other story is called "A Matter of Identity". Rather than having a consistent false belief about his situation, this patient dealt with his amnesia by constantly re-evaluating and re-explaining his situation. He would greet whoever was in the room over and over again, each time with a different name. Much like "The Lost Mariner", he was unaware of his condition.
Steve Wozniak suffered from anterograde amnesia for approximately five weeks in 1981 following the crash of an ultralight plane he piloted.
Anterograde amnesia in fiction
Anterograde amnesia has also been featured in fiction:
- The 1985 short story A Clean Escape by John Kessel, in which a psychiatrist torments a man suffering from Korsakov's syndrome. It was adapted into an audio drama for Sci Fi Channel's Seeing Ear Theatre. [link]
- 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 film Memento, presented in short reverse-chronological scenes, gives viewers some feeling for the confusion of its amnesiac protagonist.
- The November 5, 2003 episode "Twilight" of science fiction TV series 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.
- The 1940 satire The Great Dictator starred 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 2003 animated comedy Finding Nemo features the voice of Ellen DeGeneres as Dory, a regal blue-tang fish with short-term memory loss (for example, she calls Nemo by various names -- Chico, Bingo, Harpo, Fabio -- but when she actually meets Nemo she doesn't remember that's who she's been seeking).
- 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 World War 2 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
- 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 did he kidnap him despite being ordered by Maleficent to do so.
See also
External links
- http://www.memorylossonline.com/glossary/anterogradeamnesia.html
- http://neurology.health-cares.net/anterograde-amnesia.php
- http://www.thebrain.mcgill.ca/flash/d/d_07/d_07_p/d_07_p_oub/d_07_p_oub.htm
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