Amnesia is a disease with symptoms of lack of memory or incomplete memories of the events. It can be spontaneous and often temporary. Memories come back in chronological order, starting with the oldest. The memories of the last events preceding the amnesia often do not come back.
Causes of amnesia
Organic (in particular, head trauma, organic brain disease, alcoholism, drugs or other substances poisoning)

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Psychological (e.g., displacing memories about the trauma). Such amnesia is called psychogenic.

Types of amnesia
Retrograde amnesia— the patient does not remember events that occurred before the amnesia.

Anterograde amnesia— the patient loses the ability to remember events after the onset of illness (caused, for example, by injury or stress). He can remember everything that happened before. Patient may suffer from both retrograde and anterograde amnesia due to damage to middle temporal areas and especially in the hippocampus (Lezak, 1995).

Amnesia of fixation — memory disorders on current (more than a few minutes) events. It is a component of Korsakoff’s syndrome.

Traumatic amnesia is the result of a head injury (a hit, a fall on the head). Traumatic amnesia is often temporary.

Korsakoff’s syndrome is a severe anterograde and retrograde amnesia caused by lack of vitamin B1 in the brain, in combination with other symptoms. The reason is often alcoholism, although other causes, such as severe malnutrition, can lead to the same syndrome (Kolb & Whishaw, 1990).

Dissociative amnesia is when the facts of personal life are forgotten, but there is memory for generic knowledge. Dissociative amnesia is usually the result of trauma.

Localized amnesia— the patient forgets everything that happened in a limited period of time.

Selective amnesia— the patient forgets some of the events that occurred during a limited period of time.

Generalized amnesia— the patient forgets everything that happened in a limited period of time and some events before.

Continuous amnesia— patient doesn’t remember new events, but also forgets some of old. It can occur extremely rare during dissociative amnesia.

Dissociative Fugue is a more severe disease than dissociative amnesia. Patients with dissociative Fugue suddenly leave to another place and completely forget their biography and personal details up to name. Sometimes, they take a new name and a new job. Fugue state can last from several hours to several months, occasionally longer, after which patients also suddenly remember their past. They can forget everything that happened during the Fugue state.

Childhood amnesia is the inability of all people to remember what happened to them in infancy and early childhood. The reason for this is probably the lack of development of relevant areas of the brain.
Post-hypnotic amnesia— inability to remember what happened during hypnosis.

Psychogenic amnesia
It has no organic basis and arise as a result of defense mechanisms.
Hysterical amnesia— the development of the concept of hysterical amnesia is associated with the names of Jean-Martin Charcot, Pierre Janet, Josef Breuer and Sigmund Freud. It must be distinguished from the hysteria of traumatic origin (caused by psychological trauma or experiences of extreme stress and hysteria as a neurosis of transfer, associated, according to early psychoanalytical concepts, internal structural conflict, and regression of libido to the objects of the Oedipal phase of development. The hysterical amnesia of the traumatic nature is caused by the action of the protective mechanism of dissociation (Turkington & Turkington, 2002).

According to the concept of Charcot and Breuer, while experiencing a traumatic situation, some people have so-called hypnotic state — the state of self-hypnosis (Dell & O’Neil, 2009). In this altered state of consciousness is going on encoding of the memory elements corresponding to the experience of this situation. In some cases, these memories, forming independent structure, which lacks associative connection with the rest of the system of autobiographical memories, cannot be played arbitrarily. Access to them is possible only in an altered state of consciousness, which is achieved by using hypnotic trance techniques. According to psychoanalytic concepts, amnesia, caused by the action of displacement can be overcome by understanding the displaced material. The latter is achieved through the application of the method of free associations in analysis.

Fugue amnesia is an amnesia with dissociative nature. This type of psychogenic amnesia occurs during dissociative Fugue— flight response in situations of trauma or extreme stress. The main feature of dissociative Fugue is sudden, unplanned departure. Dynamics of dissociative Fugue is characterized by the double passage through the barrier of amnesia. First barrier occurs immediately after the start of the Fugue. The barrier takes important personal information and memories related to the past life of the individual. First amnestic barrier corresponds to a change of personal identity of the individual. Second amnestic barrier occurs after the termination of the Fugue state, when the memories taken by the first amnestic barrier are back. With the passage of the second amnestic barrier is lost “Fugue” personal identity and returns the same identity of the individual.

Multiple personality is a dissociative disorder, the main etiological factor of which is the chronic trauma of childhood in the context of a relationship with a significant adult (usually parents or persons substituting them). The affliction of multiple personality disorder, (or dissociated identity disorder in the DSM-IV) is sometimes mistakenly diagnosed as schizophrenia. MPD is characterized by multiple episodes of amnesia referred to the number of traumatic situations of childhood and the events that took place during the so-called switching. That is when one alter personality has lost control over the behavior of the individual to another alter-personality. As in dissociative Fugue, amnesia at MPD, tend to have a dissociative nature. Dissociative amnesia in the majority of cases (if they are not accompanied by impaired functioning of the relevant departments of the brain) is invertible. Recovery of dissociated material is usually complete and occurs either spontaneously or with the use of hypnotic and trance techniques.

    References
  • Dell, P. & O’Neil, J. (2009). Dissociation and the dissociative disorders. New York: Routledge.
  • Kolb, B. & Whishaw, I. (1990). Fundamentals of human neuropsychology. New York: Freeman.
  • Lezak, M. (1995). Neuropsychological assessment. New York: Oxford University Press.
  • Turkington, C. & Turkington, C. (2002). The encyclopedia of the brain and brain disorders. New York, NY: Facts on File.