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  • the true identity and current whereabouts of Philip Staufen, also known as "Mr. Nobody", who wandered into a Toronto hospital in 1999 and was diagnosed with amnesia, are still unknown despite an international search?

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Amnesia
Classification and external resources
ICD-10 F04, R41.3
ICD-9 294.0, 780.9, 780.93
MeSH D000647

Amnesia (from Greek Ἀμνησία) is a condition in which memory is disturbed or lost. Memory in this context refers either to stored memories or to the process of committing something to memory. The causes of amnesia have traditionally been divided into the "organic" or the "functional". Organic causes include damage to the brain, through physical injury, neurological disease or the use of certain (generally sedative) drugs. Functional causes are psychological factors, such as mental disorder, post-traumatic stress or, in psychoanalytic terms, defense mechanisms. Amnesia may also appear as spontaneous episodes, in the case of transient global amnesia.[1]

Contents

Forms of amnesia

  • In anterograde amnesia, the ability to memorise new things is impaired or lost. A person may find themselves constantly forgetting information, people or events after a few seconds or minutes, because the data does not transfer successfully from their conscious short-term memory into permanent long-term memory (or possibly vice versa)
  • In retrograde amnesia, a person's pre-existing memories are lost to conscious recollection, beyond an ordinary degree of forgetfulness. The person may be able to memorise new things that occur after the onset of amnesia (unlike in anterograde amnesia), but is unable to recall some or all of their life or identity prior to the onset

It should be noted, however, that there are different types of memory, for example procedural memory (i.e. automated skills) and declarative memory (personal episodes or abstract facts), and often only one type is impaired. For example, a person may forget who he is, but still retain a masterful ability to play piano.

In addition, the terms are used to categorize patterns of symptoms rather than to indicate a particular cause (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 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. Some sufferers claim that their amnesia changes from a neurological condition to also being a psychological condition, whereby they lose confidence and faith in their own memory and accounts of past events.

Another effect of some forms of amnesia may be impaired ability to imagine future events. A 2006 study showed that future experiences imagined by amnesiacs with bilaterally damaged hippocampus lacked spatial coherence, and the authors speculated that the hippocampus may be responsible for binding different elements of experience together when re-experiencing the past or imagining the future.[2]

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." [3] 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.
  • 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.

See also

Notes


Simple English

Amnesia is a what doctors call a loss or disturbance of memory. In simple terms, it is a loss of memory, that is to say, a person cannot remember certain things. There are two "main types":

  • Anteretrograde amnesia: Short term memory is not transferred to long-term memory any more: This means the person is unable to create new memories.
  • Retrograde amnesia: The person can no longer recall certain events that happened in the past. This has nothing to do with simply forgetting things.

Some of the more common amnesias include:

  • Caused by a trauma, for example a head injury; called post-traumatic amnesia.
  • Dissociative amnesia: Here the cause is psychological, and usually not related to physical damage in the brain. This includes
    • Repressed memory (where it is not possible to remember a specific event) - The memory is usually still there, but the person blocks access to it; Stressful events such as being raped may lead to Dissociative amnesia
    • Childhood amnesia - the inability of adults to remember certain parts of their childhood.
  • Drug (usually alcohol)-induced blackout - anteretrograde amnesia, affecting the immediate past

Amnesia can be permanent, or it can be temporary. Damage to the brain, or the use of certain drugs can cause amnesia. Some of these drugs are sedatives. Another well known cause for amnesia can be drinking too much alcohol. Those kinds of causes are called organic, because they can been directly seen. Other causes cannot directly be seen, they are called functional. Rather they are psychological in their nature. People may want to shield off a traumatic event they witnessed, for example.








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