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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 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.
This form of amnesia is often referred to as "short-term memory loss," such as in the movies Memento, 50 First Dates, 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 is also induced by some medications. Benzodiazepines 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). 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 Edit
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.
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.
References & BibliographyEdit
- Jaffe, P.G. and Katz, A.N. (1975) Attenuating anterograde amnesia in Korsakoff's psychosis, Journal of Abnormal Psychology 84: 559-62.
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