Amnesia is a condition in which memory is disturbed or lost. The causes of amnesia have traditionally been divided into categories. 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.
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. Anterograde amnesia and retrograde amnesia, where memories created prior to the event are lost, can occur together in the same patient. To a large degree, anterograde amnesia remains a mysterious ailment because the precise mechanism of storing memories is not yet well understood, although it is known that the regions involved are certain sites in the temporal cortex, especially in the hippocampus and nearby subcortical regions.
Retrograde amnesia
Retrograde amnesia (RA) is a loss of access to events and information of the past after the onset of disease or injury . RA is often temporally graded, consistent with Ribot's Law: more recent memories closer to the traumatic incident are more likely to be forgotten than more remote memories.
However, there are different types of memory, for example procedural memory (i.e. automated skills) and declarative memory (personal episodes or abstract facts), 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). 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: the medial temporal lobes and especially the hippocampus.
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 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.
There are two types of amnesia: retrograde amnesia (loss of memories that were formed shortly before the injury) and anterograde amnesia (problems with creating new memories after the injury has taken place). Both retrograde and anterograde forms may be referred to as PTA, or the term may be used to refer only to anterograde amnesia.
Frequently the last symptom to ameliorate after a loss of consciousness, anterograde amnesia may not develop until hours after the injury. A common example in sports concussion is the quarterback who was able to conduct the complicated mental tasks of leading a football team after a concussion, but has no recollection the next day of the part of the game that took place after the injury. Retrograde amnesia sufferers may partially regain memory later, but memories are not regained with anterograde amnesia because they were not encoded properly.
The term "posttraumatic amnesia" was first used in 1928 in a paper by Symonds to refer to the period between the injury and the return of full, continuous memory, including any time during which the patient was unconscious.
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. Psychogenic amnesia is defined by (a) the presence of retrograde amnesia (the inability to retrieve stored memories leading up to the onset of amnesia), and (b) an absence of anterograde amnesia (the inability to form new long term memories). Dissociative amnesia is due to psychological rather than physiological causes and can sometimes be helped by therapy.
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, and is typically preceded by severe stress and/or depressed mood. Fugue state is very rare, and usually resolves over time, often helped by therapy. 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. Situation-specific amnesia occurs as a result of a severely stressful event, as in post-traumatic stress disorder, child sex abuse, military combat or witnessing a family member's murder or suicide, and is somewhat common in cases of severe and/or repeated trauma.
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. This is not the same as amnesia, which is a term for any instance in which memories are either not stored in the first place (such as with traumatic head injuries when short term memory does not transfer to long term memory) or forgotten.
The term is used to describe memories that have been dissociated from awareness as well as those that have been repressed without dissociation. Repressed memory syndrome, the clinical term used to describe repressed memories, is often compared to psychogenic amnesia, and some sources compare the two as equivalent.
According to proponents of the hypothesis, repressed memories may sometimes be recovered years or decades after the event, most often spontaneously, triggered by a particular smell, taste, or other identifier related to the lost memory, or via suggestion during psychotherapy.
The existence of repressed memories is a controversial topic in psychology; some studies have concluded that it can occur in victims of trauma, while others dispute it. According to the American Psychological Association, it is not currently possible to distinguish a true repressed memory from a false one without corroborating evidence.
A fugue state, formally dissociative fugue or psychogenic fugue (DSM-IV Dissociative Disorders 300.13), is a rare psychiatric disorder characterized by reversible amnesia for personal identity, including the memories, personality and other identifying characteristics of individuality. The state is usually short-lived (hours to days), but can last months or longer. Dissociative fugue usually involves unplanned travel or wandering, and is sometimes accompanied by the establishment of a new identity. After recovery from fugue, previous memories usually return intact, but there is complete amnesia for the fugue episode. Additionally, an episode is not characterized as a fugue if it can be related to the ingestion of psychotropic substances, to physical trauma, to a general medical condition, or to psychiatric conditions such as delirium, dementia, bipolar disorder or depression. Fugues are usually precipitated by a stressful episode, and upon recovery there may be amnesia for the original stressor (Dissociative Amnesia).
Lacunar amnesia is the loss of memory about one specific event. It is a type of amnesia that leaves a lacuna (a gap) in the record of memory.
According to Steven Johnson, (the author of Mind Wide Open: Your Brain and the Neuroscience of Everyday Life):
"Scientists believe memories are captured and stored by two separate parts of the brain, the hippocampus, the normal seat of memory, and the amygdala, one of the brain's emotional centers. People who, due to hippocampus damage, are incapable of forming long-term memories can still form subconscious memories of traumatic events if their amygdala is intact. Someone suffering from the Memento condition would likely have a feeling of general unease encountering a person who had harmed them in the past, though they wouldn't be able to put their finger on why. As the plot of Eternal Sunshine correctly suggests, the brain is designed to preserve emotionally strong memories. Even amnesiacs, under the right circumstances, can remember their past feelings."
Furthermore, according to Alex Chadwick speaking on NPR:
"Some scientists now believe that memories effectively get rewritten every time they're activated. Studies on rats suggest that if you block a crucial chemical process during the execution of a learned behavior - pushing a lever to get food, for instance - the learned behavior disappears. The rat stops remembering. Theoretically, if you could block that chemical reaction in a human brain while triggering a specific memory, you could make a targeted erasure. Think of a dreadful fight with your girlfriend while blocking that chemical reaction, and zap! The memory's gone."
Daniel Goleman, in his book Vital Lies, Simple Truths, defines a lacuna as :
"... lacuna, from the Latin for gap or hole, to refer to the sort of mental apparatus that diversionary schemas represent. A lacuna is, then, the attentional mechanism that creates a defensive gap in awareness. Lacunas, in short, create blind spots "
Childhood amnesia (also known as infantile amnesia) is the common inability to remember events from one's own childhood. Sigmund Freud notoriously attributed this to sexual repression, while modern scientific approaches generally attribute it to aspects of brain development or developmental psychology, including language development
Transient global amnesia (TGA) is "one of the most striking syndromes 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. A person in a state of TGA exhibits no other signs of impaired cognitive functioning but recalls only the last few moments of consciousness plus deeply-encoded facts of the individual’s past, such as his or her own name.
Source amnesia is a memory disorder in which someone can recall certain information, but they do not know where or how they obtained the information.
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 (non-self) sources to verify the accuracy of memories.
Memory distrust syndrome is associated with source amnesia, which prohibits full recollection of how one acquired a specific memory. Additionally, memory distrust syndrome involves confusion concerning the content or context of events, a highly attributable factor to confabulation in brain disease.
The overwhelming propensity to accept information from external sources (i.e. an interrogator) based on the influence of susceptibility has led to well documented false confessions. In addition, the credibility of a witness account who suffers from memory distrust syndrome is more questionable. In a parallel situation, amnesic individuals may have a greater propensity to have their memory manipulated and perhaps perform non-advantageous acts on the "direction" of external sources and have difficulty in differentiating imaginary and real experiences. Since the criminal law system considers source amnesia pathology to be an identified and natural occurrence, psychiatrists should increasingly take assessment and identification measures to isolate such a disorder in accused individuals and eye-witnesses.
A blackout is a phenomenon caused by the intake of alcohol or other substance in which long term memory creation is impaired or there is a complete inability to recall the past. Blackouts are frequently described as having effects similar to that of anterograde amnesia, in which the subject cannot create memories after the event that caused amnesia. 'Blacking out' is not to be confused with the mutually exclusive act of 'passing out', which means loss of consciousness. Research on alcohol blackouts was begun by E. M. Jellinek in the 1940s. Using data from a survey of Alcoholics Anonymous (AA) members, he came to believe that blackouts would be a good predictor of alcoholism. However, there are conflicting views as to whether this is true.
Korsakoff's syndrome (also called Korsakov's syndrome, Korsakoff's psychosis, or amnesic-confabulatory syndrome), is a neurological disorder caused by the lack of thiamine (vitamin B1) in the brain. The syndrome is named after Sergei Korsakoff, the neuropsychiatrist who popularized the theory.
Drug-induced amnesia 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, or likely to be particularly traumatic. Such drugs are also referred to as "premedicants." Most commonly a 2'-halogenated benzodiazepine such as midazolam or flunitrazepam is the drug of choice, although other strongly amnestic drugs such as propofol or scopolamine 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 (ECT), 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. Today, ECT is most often recommended for use as a treatment for severe depression which has not responded to other treatment, and is also used in the treatment of mania and catatonia. It was first introduced in 1938 and gained widespread use as a form of treatment in the 1940s and 1950s.
Electroconvulsive therapy can differ in its application in three ways: electrode placement, frequency of treatments, and the electrical waveform of the stimulus. These three forms of application have significant differences in both adverse side effects and positive outcomes. After treatment, drug therapy is usually continued, and some patients receive continuation/maintenance ECT. In the United Kingdom and Ireland, drug therapy is continued during ECT.
Informed consent is a standard of modern electroconvulsive therapy. According to the Surgeon General, involuntary treatment is uncommon in the United States and is typically only used in cases of great extremity, and only when all other treatment options have been exhausted and the use of ECT is believed to be a potentially life saving treatment. However, caution must be exercised in interpreting this assertion as, in an American context, there does not appear to have been any attempt to survey at national level the usage of ECT as either an elective or involuntary procedure in almost twenty years. In one of the few jurisdictions where recent statistics on ECT usage are available, a national audit of ECT by the Scottish ECT Accreditation Network indicated that 77% of patients who received the treatment in 2008 were capable of giving informed consent.
Despite the fact that the majority of psychiatric clinicians regard ECT as a safe and effective procedure, surveys of public opinion, the testimony of former patients, legal restrictions on its use and disputes as to the efficacy, ethics and adverse effects of ECT within the psychiatric and wider medical community indicate that the use of ECT remains controversial. This is reflected in the recent decision by the FDA's Neurological Devices Advisory Panel to maintain ECT devices in the Class III device category for high risk devices except for patients suffering from catatonia. This will result in the manufacturers of such devices having to do controlled trials on their safety and efficacy for the first time. In justifying their position panelists referred to the memory loss associated with ECT and the lack of long-term data.
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.
Congenital (developmental) prosopamnesia involves an inborn difficulty in remembering faces, but having intact facial recognition and perception abilities. These abilities can be tested using the Cambridge Face Perception and Cambridge Facial Memory Test, available online. A case report of congenital prosopamnesia demonstrated a subject's inability to neurologically "adapt" to images of faces using functional Magnetic Resonance Imaging (fMRI). The authors relate this deficiency to the brain's inability to maintain a stable perception of the face long enough to encode it into long-term memory.
Prosopamnesia should not be confused with the similar condition prosopagnosia, which is characterized by a difficulty perceiving faces. An inability to "see" faces in such a manner will naturally be associated with prosopamnesia, as a facial memory trace cannot be formed without an ability to initially see the face.
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. Psychogenic amnesia is defined by (a) the presence of retrograde amnesia (the inability to retrieve stored memories leading up to the onset of amnesia), and (b) an absence of anterograde amnesia (the inability to form new long term memories). Dissociative amnesia is due to psychological rather than physiological causes and can sometimes be helped by therapy.
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, and is typically preceded by severe stress and/or depressed mood. Fugue state is very rare, and usually resolves over time, often helped by therapy. 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. Situation-specific amnesia occurs as a result of a severely stressful event, as in post-traumatic stress disorder, child sex abuse, military combat or witnessing a family member's murder or suicide, and is somewhat common in cases of severe and/or repeated trauma.
