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Psychogenic Amnesia or Dissociative amnesia is defined by DSM-IV as an inability to recall important personal information, usually of a traumatic or stressful nature, that is too extensive to be explained by ordinary forgetfulness. No structural or brain damage is evident and the memory deficits are precipitated by psychological stressors. Despite the fact that no damage to the brain is evident there are some hypothesis that psychogenic amnesia is related to how emotional processes influence brain activity.

DIFFERENT TERMS
Many different terms have been used in order to describe this controversial type of amnesia. The term "Psychogenic amnesia" answers questions such as when and in what circumstances a psychological stress is sufficient to cause memory impairment. DSM-IV uses the term "Dissociative amnesia", as a part of dissociative disorders in which the functions of memory, identity, perception and consciousness are separated (dissociated). "Dissociative amnesia" is also a more accepted psychiatric term. The term "Functional amnesia" is also used in order to show that there is no damage or injury to the brain and to distinguish functional amnesia from organic amnesia and from ordinary forgetting. The term "Hysterical amnesia" has a functional psychodynamic origin, it is referred to the past literature and makes assumes about the degree to which memory loss results from unconscious processes.

CATEGORIES AND TYPES
Psychogenic amnesia includes two main categories. The first one is called Global Psychogenic Amnesia which is generalized and refers to an inability to recall events after a specific time and up to the present. The second one is the Amnesia for Specific Situations which is circumscribed or selective. Circumscribed or selective amnesia is a failure to recall some aspects during a certain period of time. The Global Psychogenic Amnesia includes the Psychogenic Fugue and the Psychogenic Retrograde Amnesia. The Amnesia for Specific Situations includes the Amnesia of Offences and the Amnesia after Post-Traumatic Stress Disorder (PTSD). The distinguish between complete (no memory for the event) and partial (less memory of a certain event) psychogenic amnesia is helpful for the understanding of the different types of psychogenic amnesia.

Psychogenic (or dissociative) Fugue/Symptoms
The Psychogenic Fugue, from the Latin word "fugere" which means "to flee", is characterized by the sudden loss of all past autobiographical memory and of the sense of personal identity, usually associated with a period of wandering which lasts a few hours or days. The factors predisposing to fugue state can be: a precipitating stress (e.g. marital or emotional discord, financial problems, bereavement etc), depressed mood, suicide attempts, past history of alcohol abuse or past history of transient organic amnesia caused by head injury, epilepsy, hypoglycemia or some other causes. Furthermore, the psychogenic fugue can also be considered as a specific symptom which characterizes the dissociative identity disorder known as multiple personality disorder.

Psychogenic (or functional) Focal Retrograde Amnesia/Symptoms
Focal Retrograde Amnesia may occur with or without manifest organic brain damage. In Psychogenic Focal Retrograde Amnesia the patient loses memories of events that occurred prior to onset or stressful event. Moreover, the subject loses memories for the entirety of his/her previous life but there is not necessarily loss of the personal identity or a wandering period as in psychogenic fugue. Patients sometimes refer that they cannot recognize familiar faces and surroundings. Some researchers propose that focal retrograde amnesia deserve to be classified separately from organic and psychogenic forms under the label of functional retrograde amnesia.

Amnesia of Offences/Symptoms
Amnesia of Offences is most common in cases of homicide and the offenders imply that they don't remember their crime. This type of amnesia appears to occur in three types of circumstances such as crimes of passion, alcohol abuse or intoxication or if there is an accompanying diagnosis of a psychosis, such as schizophrenia. Amnesia of Offences has to be differentiated from the Simulated or Malingered Amnesia where the offenders pretend that they are amnesics in order to avoid responsibility for their acts or obstruct police investigation. Whereas Interviews don't seem to be helpful in that specific case there are some tests that have been used in order to investigate if someone is amnesic or not, such as the Symptom Validity Test (SVT) or the Structured Inventory of Malingered Symptomatology (SIMS) and both of them give encouraging results. During SVT the defendant is asked a series of dichotomous (true-false) questions about the crime and the circumstances under which it took place. The defendant is instructed to guess in case he does not know the right answers. The test has to do with the fact that purely random responding will result in about 50% of the answers being correctly answered. Individuals who perform significantly below chance avoid correct alternatives and this implies that they know the correct answers and feign memory impairment. The SIMS consists of dichotomous (true-false) items grouped into five subscales which correspond to symptoms domains that are sensitive to malingering. The items of the subscales refer to bizarre experiences or to unrealistic symptoms. The idea is that malingerers will exaggerate and so will endorse unrealistic symptoms.

Amnesia after PTSD/Symptoms
The relationship between memory and PTSD, which can be caused by exposure to a traumatic event such as physical or sexual abuse, violence, combat, natural disaster or accident, is remarkable. On the one hand, patients often have difficulty in retrieving a complete memory of a traumatic event. Their recall is fragmented and poorly organized and they have difficulty in recalling the exact temporal order of the events. On the other hand, patients report a high frequency of intrusive memories involving re-experiencing aspects of the event in a very vivid and emotional way. The interaction between emotional processing and cognitive memorizing is for patients with PTSD of special interest.

Organic Amnesia and Psychogenic Amnesia
Psychogenic and Organic Amnesia, even if they sometimes coexist, are different. Organic Amnesia is a neurological disorder that is based on brain damage and affects the mechanisms of memory and learning. There is usually a damage in the medial temporal region and also in the diencephalic midline (thalamus-hypothalamus). In organic disorders anterograde amnesia can be presented as well as the retrograde amnesia. Patients ask constantly questions ("Where am I?", "What I am doing here?") but they rarely suffer identity loss. In conclusion, as far as concerns the organic aetiology, it includes cognitive impairments during or after organic damage, neurological symptoms like hemiplegia, no evidence of second gains like malingering amnesia (see also "Amnesia of Offences"), recent memory (temporarily storing and managing information) is more affected than remote memory (long past information) and there is likely partial recovery. The anterograde and procedural memory usually remain intact but not always. In Psychogenic Amnesia, patients lose their identity. Sometimes, Psychogenic Amnesia is the result of a severe organic background and sometimes people who are susceptible to Psychogenic Amnesia have previous psychiatric history. Psychogenic Amnesia influences the episodic autobiographical memory whereas the semantic memory is unaffected. To summarize, in psychogenic aetiology emotional stress comes before any cognitive impairment; patients are emotionally distressed and usually have psychiatric background and there is evidence that suggests that psychogenic amnesia correlates with malingering amnesia when patients want to gain something, e.g. avoid criminal accusations. Finally, patients' behavior is inconsistent and unusual and they often give "don't know" answers. So, it is difficult to distinguish the borders of those two types of amnesia and that is why their difference is controversial. It is suggested that the criteria used in clinical practice to separate functional and organic factors are limited. This may be because, either organic or psychogenic factors could be involved in the aetiology of amnesia, as they have similar memory impairments, such as difficulty in retrieval. Future research, conducted by functional brain imaging, is needed to explore the nature of retrieval deficits.

Brain Abnormalities
In Psychogenic Amnesia, the focus is not on brain damages but on diffused brain abnormalities. The debate about where the memory is localised is a long-lasting one and the consensus now is that there is not a singular locus and the memory mechanism is a complex system. Even more when psychological reasons cause brain disturbance it is more difficult to define the affected area.

What causes imbalance in the brain and leads to Psychogenic Amnesia
Psychogenic Amnesia is associated with a stress stimulus, and it differs from person to person. Previous research suggests that there are some common characteristics that give an overall view of the brain activity when a stressor stimulates it. The stressful events can be provoked by recent events or can be revealed from repression memories that instantly appear and activate the brain. The latter memories, don't always cause dissociative amnesia. When a stressful event happens the autobiographical memory blocks and causes an imbalance in hormones and there is a release of glucocorticoid and mineralcorticoid.

Where is this imbalance localised
Previous studies have found that when there is an autobiographical episodic memory loss the hippocampal region becomes deactivated and the prefrontal cortex becomes active instead. However, when there is a sort of memory recovery the prefrontal cortex begins to deactivate and hippocampus to activate. In some case studies during memory retrieval tasks, there is a deactivation of medial-temporal structures and hippocampus but an activation in anterior medial-temporal lobe and amygdala. There is not an obvious causality between psychological stimulus and brain activation but, in the presence of a stressor, activation or deactivation can always take place in specific regions of the brain.

Other Brain regions associated with Psychogenic amnesia
Amygdala that is responsible for emotional regulation is related with the prefrontal section and especially the orbitofrontal cortex and those areas are involved in Psychogenic Amnesia. The orbitofrontal cortex is strongly associated with autobiographical memory retrieval. Other memory systems that are connected with psychogenic amnesia are the neocortical structures, the basal ganglia and the motor-premotor regions. To summarize, using PET, FMRI, EEG brain metabolism can be detected in patients with psychogenic amnesia. The FMRI finds activity in medial temporal and dorso-lateral frontal regions. Moreover, EEG scans can investigate if there is any disease that accompanies 'psychogenic forgetting'. However, we should also be aware that there are no group studies available that examine potential functional brain abnormalities and the external validity is weak. There is also a difficulty in developing a proper design applicable to all patients. Finally, patients are not examined and assessed with exactly the same tasks and the results need further exploration.

ASSESSMENT
Although the general rule is that an assessment of a memory disorder is more or less straight forward, since psychogenic amnesia covers a big range of different terminologies it is important when assessing psychogenic amnesia to keep in mind the comorbidity of disorders which may be present.

There are standard tests specially constructed to answer specific questions. The interpretation of scores on these specially constructed tests depends on comparing patient scores with those of matched control subjects. If such standardized tests are to be useful, then they should be reliable, cover a range of performance levels and be reasonably quick for both the patient to complete and the clinician to invigilate and score. Apart from the standard self or clinician rating scales, there are cases where relative and family member structured interviews or assessments are important. The assessment of a close relative could provide better validation because in cases of psychogenic amnesia, patients might be impaired in recollecting certain memories or even not being able to recognize their inability to recollect those memories. This of course leaves the possibility open that patients might perform normally on a memory test or rating scale, and nevertheless, relatives still claim that the patients show memory problems in their life. As when assessing other memory disorders, in pychogenic amnesia the importance of cross validation of new memory tests against others that are already established is important, especially ecological validity if the tests are used for clinical purposes. This type of validity is best tested either by getting relatives reports on how bad the memory is in the patients everyday lives, or by directly observing the frequency of failures of memory in everyday life as for example with the Rivermead Behavioral Test (RBT).

In persistent memory impairment disorders such as in psychogenic amnesia, it is suggested that there is an entailment of transient or discrete episodes of memory loss, where in the transient amnesia case it is often accompanied by the loss of personal identity such as occurring in a psychogenic fugue state. In this state, there is a sudden loss of all autobiographical memories and the sense of a self or personal identity associated with a period of wandering. It is therefore very important to develop tests that are sensitive to autobiographical memories that were acquired premorbidly. The Autobiographical Memory Interview (AMI) by Kopelman and colleagues comprises of two subtests, the first one being the ‘Personal Semantic Memory Schedule’ taping memory for personal facts such as background information, childhood, adulthood and recent past. The second subtest is called the ‘Autobiographical Incidents Schedule’ where patients are asked to recall past episodes in their lives that are specifically and directly associated with their childhood, young adulthood and recent past.

As psychogenic amnesia shares a dissociative identity component, it is very important to include tests which are more of comprehensive assessments of the construction of the dissociation. There are two types of assessment instruments for dissociative disorders, these being the self report rating scales and the clinician rating scales. The Dissociative Experience Scale (DES) helps the understanding of the frequency of the dissociative experiences through their everyday life activities. As a self report scale, the DES is used as a screening test and not a diagnostic scale. The Clinician Administered Dissociative States Scale (CADSS) is a clinician administered measure which is much more comprehensive in its dissociative nature and as it is more time consuming, it can be used to asses patients with high DES scores as a proper diagnostic tool.

TREATMENT
Historical developments have altered the treatment of functional memory problems as psychogenic amnesia, as these types of disorders were among the most prominent presented to practitioners of the nineteenth century. Such therapies initiated many early therapeutic interventions such as the clinical application of hypnosis as well as Freud’s inaugural psychoanalytic techniques. Other forms of therapy and treatment are hypnotherapy, barbiturates and medication in specific circumstances, which are outlined below in more detail.

The most dominant view of a functional memory disturbance is based on the notion of repression. The concept of repression is that experiences are stored in memory in a fully intact form and because of the powerful troubling effects associated with the memory, the mechanism of repression is believed to keep these contents from reaching the conscious awareness. Treatment in the context of the repression model requires the patient to re experience the distressing event and accept its occurrence. This is achieved through hypnotic induction and other techniques of the classical psychoanalytic approach.

The approach most widely used in the treatment of dissociative disorders is the psychodynamic therapy which considers that behavior is influenced by the unconscious and suggests that there is a major importance on the functions of the ego, the self and the social relationships. According to this theory, it is believed that the development of an integrated self begins in childhood, and a fragmented sense of self develops as a result of our needs not being met in early childhood. The child then learns to ‘split off’ the unacceptable parts of themselves. The concept of psychodynamic theory is important for people who dissociate because the process of dissociation is about banishing the unacceptable from consciousness. Mirroring back the experiences of the patient by the psychotherapist and listening to their story is the way the psychodynamic process of psychoanalysis is made. Both hypnotherapy and psychoanalysis are somehow conjoined in the sense that they both focus on the communication process of the conscious and unconscious and are used for therapeutic interventions in dissociative symptoms ever since the nineteenth century. When in psychotherapy, it is important for the therapist to name the dissociation and talk about defenses in a way that would help normalize the behavior.

Apart from the treatment theories, there is also another distinct phase of therapy required, the one of barbiturates and of medications. The barbiturates are drugs that act as central nervous system depressants, and can produce a wide spectrum of effects, from mild sedation to total anesthesia. A well-known drug used in these situations is sodium pentothal also called the truth serum which was named after its effects. It is a psychoactive medication used to obtain information from subjects who are unable to provide it otherwise because of stress or bad effects of events, such as in the case of psychogenic amnesia. It is an intravenous injection which releases anxiety making recollection more detailed. As far as proper medication is concerned, there are no specific therapeutic agents that cure dissociative amnesia itself. However, since comorbidity is present, disorders such as depression and anxiety accompany the disorder of dissociation. In that case, psychoactive drugs such as benzodiazepines and Serzone can be used to treat accompanying disorders.