Amnesia is a condition in which one's memory

Memory

In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....

 is lost. The causes of amnesia have traditionally been divided into categories. Memory appears to be stored in several parts of the limbic system of the brain, and any condition that interferes with the function of this system can cause amnesia. 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

Transient global amnesia

Transient global amnesia is a syndrome in clinical neurology whose key defining characteristic is temporary but almost total disruption of short-term memory with a range of problems accessing older memories...

.

• Anterograde amnesia
  Anterograde amnesia
  Anterograde amnesia is a loss of the ability to create new memories after the event that caused the amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories...
  
  , is the loss of short-term memory, the loss or impairment of the ability to form new memories through memorization. People may find themselves constantly forgetting a piece of information, people or events after a few seconds or minutes, because the data does not transfer successfully from their conscious short-term memory
  Short-term memory
  Short-term memory is the capacity for holding a small amount of information in mind in an active, readily available state for a short period of time. The duration of short-term memory is believed to be in the order of seconds. A commonly cited capacity is 7 ± 2 elements...
  
   into permanent long-term memory
  Long-term memory
  Long-term memory is memory in which associations among items are stored, as part of the theory of a dual-store memory model. According to the theory, long term memory differs structurally and functionally from working memory or short-term memory, which ostensibly stores items for only around 20–30...
  
  . Primarily in older men, transient global amnesia causes severe loss of memory for minutes or hours.
• Retrograde amnesia
  Retrograde amnesia
  Retrograde amnesia is a loss of access to events that occurred, or information that was learned, before an injury or the onset of a disease....
  
  , the loss of pre-existing memories to conscious recollection, beyond an ordinary degree of forgetfulness. The person may be able to memorize
  Memorization
  Memorization is the process of committing something to memory. The act of memorization is often a deliberate mental process undertaken in order to store in memory for later recall items such as experiences, names, appointments, addresses, telephone numbers, lists, stories, poems, pictures, maps,...
  
   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. The affects of retrograde amnesia (RA) occurs on fact memory on a lower degree than its affects on autobiographical memory, which can be affected over the whole lifespan of the patient by RA. There have also been some cases where retrograde amnesia is a result of hypoglycemia in insulin-dependent diabetic patients.(The Lancet, May 1995)

However, there are different types of memory, for example procedural memory

Procedural memory

Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...

 (i.e. automated skills) and declarative memory

Declarative memory

Declarative memory is one of two types of long term human memory. It refers to memories which can be consciously recalled such as facts and knowledge. Its counterpart is known as non-declarative or Procedural memory, which refers to unconscious memories such as skills...

 (personal episodes

Episodic memory

Episodic memory is the memory of autobiographical events that can be explicitly stated. Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions in memory...

 or abstract facts

Semantic memory

Semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...

), and often only one type is impaired. For example, a person may forget the details of personal identity, but still retain a learned skill such as the ability to play the piano.

In addition, the terms are used to categorize patterns of symptoms rather than to indicate a particular cause (etiology

Etiology

Etiology is the study of causation, or origination. The word is derived from the Greek , aitiologia, "giving a reason for" ....

). 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

Episodic memory

Episodic memory is the memory of autobiographical events that can be explicitly stated. Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions in memory...

: the medial temporal lobe

Temporal lobe

The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....

s and especially the hippocampus

Hippocampus

The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

.

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

Hippocampus

The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

 lacked spatial coherence, and the authors speculated that the hippocampus may bind different elements of experience together in the process of re-experiencing the past or imagining the future.

Types and causes of amnesia

• Post-traumatic amnesia
  Post-traumatic amnesia
  Post-traumatic amnesia is a state of confusion that occurs immediately following a traumatic brain injury in which the injured person is disoriented and unable to remember events that occur after the injury. The person may be unable to state his or her name, where he or she is, and what time it...
  
  is generally due to a head injury
  Traumatic brain injury
  Traumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...
  
   (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.
• Dissociative amnesia
  Psychogenic amnesia
  Psychogenic amnesia, also known as functional amnesia or dissociative amnesia, is a memory disorder characterized by extreme memory loss that is caused by extensive psychological stress and that cannot be attributed to a known neurobiological cause...
  
  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
    Repressed memory
    Repressed memory is a hypothetical concept used to describe a significant memory, usually of a traumatic nature, that has become unavailable for recall; also called motivated forgetting in which a subject blocks out painful or traumatic times in one's life...
    
    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
    Fugue state
    A fugue state, formally dissociative fugue or psychogenic fugue , is a rare psychiatric disorder characterized by reversible amnesia for personal identity, including the memories, personality and other identifying characteristics of individuality...
    
    (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." While popular in fiction, it is extremely rare.
  • Posthypnotic amnesia is where events during hypnosis
    Hypnosis
    Hypnosis is "a trance state characterized by extreme suggestibility, relaxation and heightened imagination."It is a mental state or imaginative role-enactment . It is usually induced by a procedure known as a hypnotic induction, which is commonly composed of a long series of preliminary...
    
     are forgotten, or where past memories are unable to be recalled.
• Lacunar amnesia
  Lacunar amnesia
  Lacunar amnesia is the loss of memory about one specific event. It is a type of amnesia that leaves a lacuna in the record of memory.According to Steven Johnson, :...
  
  is the loss of memory about one specific event.
• Childhood amnesia
  Childhood amnesia
  Childhood amnesia refers to the inability of adults to retrieve episodic memories before the age of 2-4 years, as well as the period before age 10 of which adults remember fewer memories than accounted for by the passage of time...
  
  (also known as infantile amnesia) is the common inability to remember events from one's own childhood. Sigmund Freud
  Sigmund Freud
  Sigmund Freud , born Sigismund Schlomo Freud , was an Austrian neurologist who founded the discipline of psychoanalysis...
  
   notoriously attributed this to sexual repression, while modern scientific approaches generally attribute it to aspects of brain development or developmental psychology
  Developmental psychology
  Developmental psychology, also known as human development, is the scientific study of systematic psychological changes, emotional changes, and perception changes that occur in human beings over the course of their life span. Originally concerned with infants and children, the field has expanded to...
  
  , including language development
  Language development
  Language development is a process starting early in human life, when a person begins to acquire language by learning it as it is spoken and by mimicry. Children's language development moves from simple to complex. Infants start without language. Yet by four months of age, babies can read lips and...
  
  
• Transient global amnesia
  Transient global amnesia
  Transient global amnesia is a syndrome in clinical neurology whose key defining characteristic is temporary but almost total disruption of short-term memory with a range of problems accessing older memories...
  
  is a well-described medical and clinical phenomenon. This form of amnesia is distinct in that abnormalities in the hippocampus
  Hippocampus
  The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
  
   can sometimes be visualized using a special form of magnetic resonance imaging
  Magnetic resonance imaging
  Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
  
   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
  Source amnesia
  Source amnesia is an explicit memory disorder in which someone can recall certain information, but not where or how it was obtained.-Process and experimentation:...
  
  is a memory disorder
  Memory disorder
  Memory can be defined as an organism's ability to encode, retain, and recall information. Disorders of memory can range from mild to severe, yet are all a result of damage to neuroanatomical structures; either in part or in full. This damage hinders the storage, retention and recollection of memories...
  
  in which someone can recall certain information, but they do not know where or how they obtained the information.
• Memory distrust syndrome
  Memory distrust syndrome
  Memory distrust syndrome is a term coined by Gísli Guðjónsson and James MacKeith in 1982, to describe those who distrust their own memories and are motivated to rely on external sources to verify the accuracy of memories....
  
  is a term invented by the psychologist Gisli Gudjonsson
  Gisli Gudjonsson
  Gísli Hannes Guðjónsson, CBE is a Professor of Forensic Psychology at the Institute of Psychiatry of King's College London. He is an internationally renowned authority on suggestibility and false confessions whose expert testimony was the basis for the convictions of the Birmingham Six and...
  
   to describe a situation where someone is unable to trust their own memory.
• Blackout phenomenon can be caused by excessive short-term alcohol consumption, with the amnesia being of the anterograde type.
• Korsakoff's syndrome
  Korsakoff's syndrome
  Korsakoff's syndrome is a neurological disorder caused by the lack of thiamine in the brain. Its onset is linked to chronic alcohol abuse and/or severe malnutrition...
  
  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
  Confabulation
  Confabulation is the process in which a memory is remembered falsely. Confabulations are indicative of a complicated and intricate process that can be led astray at any given point during encoding, storage, or recall of a memory. Two distinct types of confabulation are often distinguished...
  
  .
• Drug-induced amnesia
  Drug-induced amnesia
  Drug-induced amnesia is amnesia caused by drugs. It may occur due to the use of recreational drugs such as alcohol, and it is used in surgery in order to make a patient forget painful or otherwise traumatic procedures.-Medical usage:...
  
  is intentionally caused by injection of an amnesiac drug to help a patient forget surgery or medical procedures, particularly those not performed under full anesthesia
  General anaesthesia
  General anaesthesia is a state of unconsciousness and loss of protective reflexes resulting from the administration of one or more general anaesthetic agents...
  
  , or likely to be particularly traumatic. Such drugs are also referred to as "premedicants." Most commonly a 2'-halogenated benzodiazepine
  Benzodiazepine
  A benzodiazepine is a psychoactive drug whose core chemical structure is the fusion of a benzene ring and a diazepine ring...
  
   such as midazolam
  Midazolam
  Midazolam is a short-acting drug in the benzodiazepine class developed by Hoffmann-La Roche in the 1970s. The drug is used for treatment of acute seizures, moderate to severe insomnia, and for inducing sedation and amnesia before medical procedures. It possesses profoundly potent anxiolytic,...
  
   or flunitrazepam
  Flunitrazepam
  Flunitrazepam is marketed as a potent hypnotic, sedative, anticonvulsant, anxiolytic, amnestic, and skeletal muscle relaxant drug most commonly known as Rohypnol...
  
   is the drug of choice, although other strongly amnestic drugs such as propofol
  Propofol
  Propofol is a short-acting, intravenously administered hypnotic agent. Its uses include the induction and maintenance of general anesthesia, sedation for mechanically ventilated adults, and procedural sedation. Propofol is also commonly used in veterinary medicine...
  
   or scopolamine
  Scopolamine
  Scopolamine, also known as levo-duboisine, and hyoscine, is a tropane alkaloid drug with muscarinic antagonist effects. It is among the secondary metabolites of plants from Solanaceae family of plants, such as henbane, jimson weed and Angel's Trumpets , and corkwood...
  
   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.
• Electroconvulsive therapy
  Electroconvulsive therapy
  Electroconvulsive therapy , formerly known as electroshock, is a psychiatric treatment in which seizures are electrically induced in anesthetized patients for therapeutic effect. Its mode of action is unknown...
  
  in which seizures are electrically induced in patients for therapeutic effect can have acute effects including both retrograde and anterograde amnesia.
• Prosopamnesia
  Prosopamnesia
  Prosopamnesia is a rare neuropsychological deficit defined by an inability to remember faces. It can be subdivided into two different types, including a 'congenital' and 'acquired' version....
  
  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
  Psychogenic amnesia
  Psychogenic amnesia, also known as functional amnesia or dissociative amnesia, is a memory disorder characterized by extreme memory loss that is caused by extensive psychological stress and that cannot be attributed to a known neurobiological cause...
  
  can arise in a variety of circumstances (e.g., committing an offence, child sexual abuse
  Child sexual abuse
  Child sexual abuse is a form of child abuse in which an adult or older adolescent uses a child for sexual stimulation. Forms of child sexual abuse include asking or pressuring a child to engage in sexual activities , indecent exposure with intent to gratify their own sexual desires or to...
  
  ) 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.
• Anterograde amnesia
  Anterograde amnesia
  Anterograde amnesia is a loss of the ability to create new memories after the event that caused the amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories...
  
  refers to the inability to create new memories due to head trauma. That is not the only cause,it is also caused by Wernicke-Korsakoff Syndrome, serebrovascular events, anoxia and other substances. The two brain regions related with this condition are medial temporal lobe and medial diencephalon. Anterograde amnesia cannot be treated with pharmacological methods due to neuronal loss.

See also

• Betrayal trauma
• Doug Bruce
  Doug Bruce
  Doug Bruce is the subject of Rupert Murray's 2005 documentary film Unknown White Male.Bruce claims to suffer from an extremely rare, and possibly purely psychological, form of retrograde amnesia. It is alleged that this has left his episodic memory blank for his entire life prior to the onset of...
  
  
• Emotion and memory
  Emotion and memory
  Emotion can have a powerful impact on memory. Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events....
  
   
• False memory
  False memory
  False memory syndrome describes a condition in which a person's identity and relationships are affected by memories which are factually incorrect but are strongly believed. Peter J...
  
  
• HM (patient)
  HM (patient)
  Henry Gustav Molaison , famously known as HM or H.M., was an American memory disorder patient who was widely studied from late 1957 until his death...
  
  
• KC (patient)
  KC (patient)
  Patient KC is a widely studied Canadian memory disorder patient who has been used as a case study in over 20 neuropsychology papers over the span of the past 25 years. In 1981, KC was involved in a motorcycle accident that left him with severe anterograde amnesia, as well as temporally graded...
  
  

• Benjaman Kyle
  Benjaman Kyle
  Benjaman Kyle is the pseudonym adopted by a man who has retrograde amnesia, or possibly dissociative fugue. He was discovered unconscious on August 31, 2004, in Richmond Hill, Georgia and is believed to be about 60 years old...
  
  
• Repressed memories
• Mr. Nobody
• Transient epileptic amnesia
  Transient epileptic amnesia
  Transient epileptic amnesia is a rare but probably underdiagnosed neurological condition which manifests as relatively brief and generally recurring episodes of amnesia caused by underlying temporal lobe epilepsy...
  
   (TEA)
• Clive Wearing
  Clive Wearing
  Clive Wearing is a British musicologist, conductor, and keyboardist suffering from an acute and long-lasting case of anterograde and retrograde amnesia, meaning that he lacks the ability to form new memories.-Musical career:...
  
  
• List of films featuring mental illness