Amnesia

Amnesia 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.

Amnesia can be temporary. As someone recovers, older memories will generally return first. The memories of the event that caused the amnesia are often never recalled.

Treatment varies according to the type of amnesia and the cause of the problem. Sufferers of amnesia should seek medical attention.

Types of amnesia

• In anterograde amnesia, new events are not transferred to long-term memory, so the sufferer will not be able to remember anything that occurs after the onset of this type of amnesia for more than a few moments. The complement of this is retrograde amnesia, where someone will be unable to recall events that occurred before the onset of amnesia. The terms are used to categorise 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 damage to the brain regions most closely associated with episodic/declarative memory: the medial temporal lobes and especially the hippocampus.

• Traumatic amnesia is generally due to a head injury (fall, knock on the head). Traumatic amnesia is often transient, the duration of the amnesia is related to the degree of injury and may give an indication of the prognosis for recovery of other functions.

• Memory loss caused by alcoholism is known as the Korsakoff's syndrome. This is caused by brain damage due to a Vitamin B1 deficiency and will be progressive if alcohol intake and nutrition pattern are not modified. It will usually improve little over time even if they are. Other neurological problems are likely to be present.

• Lacunar amnesia is the loss of memory about one specific event.

• Fugue state is also known as dissociative fugue. It is caused by psychological trauma and is usually temporary. 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" [1] (http://www.merck.com/mrkshared/mmanual/section15/chapter188/188c.jsp).

• Childhood amnesia (also known as Infantile amnesia) is the common inability to remember events from your 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.

• Global amnesia is total memory loss. This may be a defence mechanism which occurs after a traumatic event. Post-traumatic stress disorder can also involve the spontaneous, vivid retrieval of unwanted traumatic memories. It is believed that Mauritania's Silent Flute Man suffered from this condition.

• Posthypnotic amnesia is where events during hypnosis are forgotten, or where past memories are unable to be recalled.

See also

• Source amnesia is a memory disorder in which someone can recall certain information, but they do not know where or how they obtained it.
• 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.

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