Recovered memory is the apparent resurrection of the memory of events that had been forgotten or suppressed for a long time. Retrograde amnesia after physical or emotional trauma (i.e., traumatic amnesia), or the suppression of painful memories from any cause, is well known. However the mechanisms that lead to recovery of long forgotten memories are not well understood, and the authenticity of these recovered memories has often been challenged; in some cases recovered memories are fictitious, although in other cases they may be authentic. 
The issues surrounding recovered, or false memories have sparked one of the greatest controversies in the mental health profession of recent times. Some researchers have proposed that memories of extreme trauma are buried in the subconscious by a special process, and are later reliably recovered. Others consider that genuinely traumatic events are seldom truly forgotten, and that the scientific evidence indicates that traumatic amnesia is a myth.  However, traumatized individuals exhibit a range of memory impairments, and research on children's and adults' encoding and memory of trauma stimuli has provided some support for models of repression and traumatic amnesia.
Amnesia is partial or complete loss of memory that goes beyond mere forgetting. Often it is temporary and involves only part of a person's experience. Amnesia is often caused by an injury to the brain, for instance after a blow to the head, and sometimes by psychological trauma. Anterograde amnesia is a failure to remember new experiences that occur after damage to the brain; retrograde amnesia is the loss of memories of events that occurred before a trauma or injury. For a memory to become permanent (consolidated), there must be a persistent change in the strength of connections between particular neurons in the brain. Anterograde amnesia can occur because this consolidation process is disrupted; retrograde amnesia can result either from damage to the site of memory storage or from a disruption in the mechanisms by which memories can be retrieved from their stores. Many specific types of amnesia are recognised, including:
- Infantile (childhood) amnesia, the normal inability to recall events from early childhood. There are various theories about this; some believe that language development is important for efficient storage of long term memories, some believe that early memories do not persist because the brain is still developing.
- Hysterical amnesia (dissociative Fugue or fugue amnesia), a rare condition linked to severe psychological trauma. It is characterised by epidode(s) of "an 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." Usually, the memory returns within a few days, although memory of the trauma may remain incomplete.
The form of amnesia that is linked with recovered memories is dissociative amnesia (formerly known as psychogenic amnesia). This results from a psychological cause, not by direct damage to the brain, and is a loss of memory of significant personal information, usually about traumatic or extremely stressful events. Usually this is seen as a gap or gaps in recall for aspects of someone's life history, but with severe acute trauma, such as during wartime, there can be a sudden acute onset of symptoms 
Our memories can be accurate, but are not always accurate. For example, eyewitness testimony even of relatively recent dramatic events is notoriously unreliable.  Misremembering results from confusion between memories for perceived and imagined events, which may result from overlap between particular features of the stored information comprising memories for perceived and imagined events. Our memories are always a mix of factual traces of sensory information overlaid with emotions, mingled with interpretation and "filled in" with imaginings. Thus there is always skepticism about how valid a memory is as evidence of factual detail. Some believe that accurate memories of traumatic events are often repressed, but remain in the subconscious mind, from where they can be recovered by appropriate therapy. Others believe that truly traumatic events are never forgotten in this way, although often people may not disclose their memories to others. This is a difficult area to study, and unambiguous conclusions are hard to draw. In one study where victims of documented child abuse were reinterviewed many years later as adults, a high proportion of the women denied any memory of the abuse.
Those who doubt the existence of "traumatic amnesia" note that various manipulations can be used to implant false memories (sometimes called "pseudomemories"). These can be compelling for those who develop them, and can include details that make them credible to others. A classic experiment in memory research, conducted by Elizabeth Loftus, became widely known as "Lost in the Mall"; in this, subjects were given a booklet containing three accounts of real childhood events written by family members and a fourth account of a wholly fictitious event of being lost in a shopping mall. A quarter of the subjects reported remembering the fictitious event, and elaborated on it with extensive circumstantial detail. This experiment inspired many others, and in one of these, Porter et al. could convince about half of his subjects that they had survived a vicious animal attack in childhood.
While such studies have been criticized  in particular about whether the findings are really relevant to trauma memories and psychotherapeutic situations., they prompted public and professional concern about recovered memory therapy for past sexual abuse. When memories are 'recovered' after long periods of amnesia, particularly when extraordinary means were used to secure the recovery of memory, it is now widely (but not universally) accepted that the memories are quite likely to be false, i.e. of incidents that had not occurred. It is thus recognised by professional organizations that a risk of implanting false memories is associated with some types of therapy. The American Psychiatric Association advises that "...most leaders in the field agree that although it is a rare occurrence, a memory of early childhood abuse that has been forgotten can be remembered later. However, these leaders also agree that it is possible to construct convincing pseudomemories for events that never occurred. The mechanism(s) by which both of these phenomena happen are not well understood and, at this point it is impossible, without other corroborative evidence, to distinguish a true memory from a false one."  
Obviously, not all therapists agree that false memories are a major risk with psychotherapy.     Several studies have reported high percentages of the corroboration of recovered memories., and some authors have claimed that the 'false memory movement' has tended to conceal or ignore evidence of corroboration of recovered memories. Herman, in her theory of recovery from chronic Post-Traumatic Stress Disorder writes that one of the major recovery stages is the remembering and mourning of the repressed material of traumatic events.
Both true and false 'memories' can be recovered using memory work techniques, but there is no evidence that reliable discriminations can be made between them.  Some believe that memories "recovered" under hypnotism are particularly likely to be false.  According to The Council on Scientific Affairs for the American Medical Association, recollections obtained during hypnosis can involve confabulations and pseudomemories and appear to be less reliable than nonhypnotic recall. 
Serious issues arise when recovered but false memories result in public allegations; false complaints carry serious consequences for the accused. Many of those who make false claims sincerely believe the truth of what they report. A special type of false allegation, the false memory syndrome, arises typically within therapy, when people report the 'recovery' of childhood memories of previously unknown abuse. The influence of practitioners' beliefs and practices in the eliciting of false 'memories' and of false complaints has come under particular criticism. Sometimes these memories are used as evidence in criminal prosecutions.
It is generally accepted that people sometimes are unable to recall traumatic experiences. The current version (DSM-IV) of the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association, states that "Dissociative amnesia is characterized by an inability to recall important personal information, usually of a traumatic or stressful nature, that is too extensive to be explained by ordinary forgetfulness." The term "recovered memory", however, is not listed in DSM-IV or used by any mainstream formal psychotherapy modality.
Alan Scheflin, a law professor, explains that this satisfies courts that recovered memories are admissible into evidence in court. "Both those who argue that repressed memories are always false and those who argue that repressed memories are always true [...] appear to be mistaken. Although the science is limited on this issue, the only three relevant studies conclude that repressed memories are no more and no less accurate than continuous memories....” A U.S. District Court accepted repressed memories as admissible evidence in a specific case. Dalenberg argues that the evidence shows that recovered memory cases should be allowed to be prosecuted in court. The apparent willingness of courts to credit the recovered memories of complainants but not the absence of memories by defendents has been commented on "It seems apparent that the courts need better guidelines around the issue of dissociative amnesia in both populations."
Neurological Basis of Memory
The neuroscientist Donald Hebb (1904 - 1985) was the first to distinguish between short-term memory and long-term memory. According to current theories in neuroscience, things that we "notice" are stored in short-term memory for up to a few minutes; this memory depends on 'reverberating' electrical activity in neuronal circuits, and is very easily destroyed by interruption or interference. Memories stored for longer than this are stored in long-term memory. Whether information is put into this long-term store depends on its 'importance'; memories of traumatic events are important for avoiding similar events in the future, and hormones that are released during stress have a role in determining what memories are preserved. In humans, traumatic stress is associated with secretion of epinephrine and norepinephrine (adrenaline and noradrenaline) from the adrenal medulla and cortisol from the adrenal cortex. In the brain, the limbic system is a set of interconnected regions, including the hippocampus and amygdala, which are involved in memory storage and retrieval and in assigning emotional significance to sensory inputs, and cortisol has powerful actions at these sites.
Although memory distortion occurs in everyday life, the brain mechanisms involved are not easy to study in the laboratory, but neuroimaging techniques have recently been applied to this subject. In particular, there have been studies of false recognition, where individuals incorrectly claim to have encountered a novel object or event, and the results suggest that the hippocampus and several cortical regions may contribute to such false recognition, while the prefrontal cortex may be involved in retrieval monitoring that can limit the rate of false recognition.
Effects of trauma on memory
'Betrayal Trauma Theory' proposes that in childhood abuse, dissociative amnesia is an adaptive response; “victims may need to remain unaware of the trauma not to reduce suffering but rather to promote survival.” When stress interferes with memory, it is possible that some of the memory is kept by a system that records emotional experience, but there is no symbolic placement of it in time or space. Traumatic memories are retrieved, at least at first, in the form of dissociated mental imprints of the affective and sensory elements of the traumatic experience. Clients have reported the slow emergence of a personal narrative that can be considered explicit (conscious) memory.
Psychiatrist Bessel van der Kolk  divided the efffects of traumas on memory functions into:
- traumatic amnesia; this involves the loss of memories of traumatic experiences. The younger the subject and the longer the traumatic event is, the greater the chance of significant amnesia. Subsequent retrieval of memories after traumatic amnesia is well documented, with examples following natural disasters and accidents, in combat soldiers, in victims of kidnapping, torture and concentration camp experiences, in victims of physical and sexual abuse, and in people who have committed murder.
- global memory impairment; this makes it difficult for subjects to construct an accurate account of their present and past history. "The combination of lack of autobiographical memory, continued dissociation and of meaning schemes that include victimization, helplessness and betrayal, is likely to make these individuals vulnerable to suggestion and to the construction of explanations for their trauma-related affects that may bear little relationship to the actual realities of their lives"
- dissociative processes; this refers to memories being stored as fragments and not as unitary wholes.
- traumatic memories’ sensorimotor organization. Not being able to integrate traumatic memories seems to be linked to post traumatic stress disorder (PTSD). 
According to van der Kolk, memories of highly significant events are usually accurate and stable over time; aspects of traumatic experiences appear to get stuck in the mind, unaltered by time passing or experiences that may follow. The imprints of traumatic experiences appear to be different from those of nontraumatic events, perhaps because of alterations in attentional focusing or the fact that extreme emotional arousal interferes with memory. van der Kolk and Fisler’s hypothesis is that under extreme stress, the memory categorization system based in the hippocampus fails, but these memories to be kept as emotional and sensory states. When these traces are remembered and put into a personal narrative, they may be condensed, contaminated and embellished upon.
When there is inadequate recovery time between stressful situations, alterations may occur to the stress-response system, some of which may be irreversible, and cause pathological responses, which may memory loss, learning deficits and other maladaptive symptoms. In animal studies, high levels of cortisol can cause hippocampal damage, which may cause short-term memory deficits; in humans, MRI studies have shown reduced hippocampal volumes in combat veterans with PTSD, adults with posttraumatic symptoms and survivors of repeated childhood sexual or physical abuse. Trauma may also interfere with implicit memory, where periods of avoidance may be interrupted by intrusive emotional occurrences with no story to guide them. A difficult issue is whether those presumably abused accurately recall their experiences. 
The Working Group on Investigation of Memories of Child Abuse of the American Psychological Association presented findings mirroring those of the other professional organizations (see External Links subpage for references to various statements made independently by these organisations). The Working Group made five key conclusions:
(1) Controversies regarding adult recollections should not be allowed to obscure the fact that child sexual abuse is a complex and pervasive problem in America that has historically gone unacknowledged;
(2) Most people who were sexually abused as children remember all or part of what happened to them;
(3) It is possible for memories of abuse that have been forgotten for a long time to be remembered;
(4) It is also possible to construct convincing pseudo-memories for events that never occurred; and
(5) There are gaps in our knowledge about the processes that lead to accurate and inaccurate recollections of childhood abuse. 
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