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Psychogenic amnesia, also known as functional or dissociative amnesia, is a disorder characterized by abnormal memory functioning in the absence of structural brain damage or a known neurobiological cause; severe cases are very rare. It is defined by the presence of retrograde amnesia or the inability to retrieve stored memories and events leading up to the onset of amnesia and an absence of anterograde amnesia or the inability to form new long term memories. In most cases, patients lose their autobiographical memory and personal identity even though they are able to learn new information and perform everyday functions normally. Other times, there may be a loss of basic semantic knowledge and procedural skills such as reading and writing.
There are two types of psychogenic amnesia, global and situation-specific. Global amnesia, also known as fugue state, refers to a sudden loss of personal identity that lasts a few hours to days. This is preceded by severe stress and/or depressed mood. Fugue state is very rare, and usually resolves over time, often helped by therapy. Situation-specific amnesia is a type of dissociative amnesia occurs as a result of a severely stressful event, as in post-traumatic stress disorder. Dissociative amnesia is due to psychological rather than physiological causes and can sometimes be helped by therapy.
Additional recommended knowledge
Memory and the brain
There are three types of memory – ultra-short-term, short-term, and long-term memory. Ultra-short-term memory lasts up to hundreds of milliseconds and short-term memory lasts from seconds to minutes while anything else longer than short-term memory is considered to be a long-term memory.
The information obtained from the peripheral nervous system (PNS) is processed in four stages - encoding, consolidating, storage, and retrieval. During encoding, the limbic system is responsible for bottlenecking or filtering information obtained from the PNS. According to the type of information given, the duration of consolidating stage varies drastically. Majority of consolidated information gets stored in the cerebral cortical networks where the limbic system record episodic-autobiographical events. These stored episodic and semantic memories can be obtained by triggering the uncinate fascicle that interconnects the regions of the temporofrontal junction area.
Emotion seems to play an important role in memory processing in structures like the cingulated gyrus, the septal nuclei, and the amygdale that is primarily involved in emotional memories. Functional imaging of normal patients reveal that right-hemisperic amygdala and ventral prefrontal regions are activated when they were retrieving autobiographical information and events. Additionally, hippocampal region is known to be linked to recognizing faces. Researchers have found that emotional memories can be suppressed via two time-differentiated neural mechanisms. 
Psychogenic and organic amnesia
Clinically, psychogenic amnesia is characterized by the loss of the ability to retrieve stored memory without having damages to the brain while organic amnesia is characterized by damages to the medial or anterior temporal and/or prefrontal regions caused by stroke, traumatic brain injury, ischemia, and encephalitis. Some characteristics that define organic amnesia is the maintenance of personal identity, basic semantic knowledge and procedural skills as well as neuroradiological images showing cerebral damage to the cortical and/or subcortical areas known to be associated with long-term memory while some characteristics that define psychogenic amnesia is the loss of personal identity, semantic knowledge, and procedural abilities at least in the early phase of amnesia as well as damage directly affecting cerebral areas critical for memory functioning that cannot be detected in clinical history or neuroradiological exams.
Imaging of psychogenic amnesia
Psychogenic amnesia is defined by the lack of structural damage to the brain, but upon functional imaging, an abnormal brain activity can be seen. Tests using functional magnetic resonance imaging suggest that patients with psychogenic amnesia are unable to retrieve emotional memories normally during the amnesic period, suggesting that changes in the limbic functions are related to the symptoms of psychogenic amnesia. By performing a positron emission tomography activation study on psychogenic amnesic patients with face recognition, it was found that activation of the right anterior medial temporal region including the amygdala was increased in the patient whereas bilateral hippocampal regions increased only in the control subjects, demonstrating again that limbic and limbic-cortical functions are related to the symptoms of psychogenic amnesia.
Patients exposed to physically or emotionally traumatic events and are at a higher risk for developing psychogenic amnesia because they seem to damage the neurons in toto in the brain. Examples of individuals at greater risk of psychogenic amnesia due to traumatic events include soldiers who have experienced combat, individuals sexually and physically abused during childhood and individuals who have been experienced domestic violence, natural disasters, or terrorist acts; essentially any sufficiently severe psychological stress, internal conflicts, or intolerable life situation.
Psychogenic amnesia is far from being completely understood and while several explanations have been proposed, none of them have been verified as the mechanism that fits all types of psychogenic amnesia. Different theories include:
Currently, various treatments are available for patients with psychogenic amnesia although no well-controlled studies on the effectiveness of different treatments exist.
Pyschogenic amnesia is a common plot device in many films and books. Notable examples include the character of Jason Bourne, Jackie Chan in Who Am I? and Goldie Hawn in Overboard.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Psychogenic_amnesia". A list of authors is available in Wikipedia.|