Classification and external resources
Amnesia is a medical condition involving the loss of memory. While memory loss can be attributable to a number of illnesses or factors including Alzheimer's disease and dementia, amnesia is often caused by head injury, brain trauma, or brain surgery. Certain states of amnesia can also be precipitated by alcohol consumption, drug use, or the effects of a stroke.
The type of memory loss involved in amnesia does not affect a person's intelligence, general knowledge, awareness, attention span, judgment, personality, or identity. People with amnestic syndrome usually can understand written and spoken words and can learn skills such as bike riding or piano playing. They do well on tests of attention and reasoning and often understand that they have a memory disorder. Unlike dementia, amnesia does not necessarily affect a person's ability to perform daily tasks or other cognitive functions; however, the memory loss caused by amnesia can be more severe.
Amnesia varies in severity and scope, but even mild amnesia can affect quality of life. Techniques for enhancing day-to-day memory and social and psychological support can help people with amnesia and their families cope.
Amnesia refers to the loss of memory responsible for knowing facts, events, information and experiences. Also called amnestic syndrome, this memory loss cannot be accounted for by problems with attention, perception, language, reasoning, or motivation. People with amnesia typically are lucid and maintain a sense of self, but they face severe difficulties in learning new information and forming new memories. They may not be able to recall memories of past experiences and information.
Though a common plot device in movies and television, amnesia occurs quite rarely in real life. It can result from damage to parts of the brain that are vital for memory processing and learning.
In order to diagnose amnesia other possible causes of memory loss, such as Alzheimer's disease, dementia, depression, brain tumor, or epilepsy must first be ruled out by a physician. This is done through taking a person's medical history, interviewing family members, and through the use of diagnostic imaging tests such as magnetic resonance imaging (MRI) a computerized tomography (CT), or electroencephalogram (EEG)—which may identify damage to or abnormalities in the brain.
Other tests might include a lumbar puncture, a cerebral angiography, and various cognitive (psychometrics) tests. A Transient Ischemic Attack(TIA)—a mini or mild stroke—should also be investigated as a possible cause.
In addition to investigating the patient's family history, triggering factors, (drug or alcohol use) and/or injury, a physician will perform a neurological exam which includes checking reflexes, sensory function, balance, and other physiological aspects of the brain and nervous system.
One effect of amnesia is the inability to imagine the future. A recent study published online in the Proceedings of the National Academy of Sciences shows that amnesiacs with a damaged hippocampus cannot imagine the future. When an otherwise healthy human being imagines the future, he or she uses their past experiences to construct a possible scenario. For example, a person who would try to imagine what would happen at a party that would occur in the near future would use his or her past experience at parties to help construct the event in the future.
Some cases of amnesia have been known to occur when a person suffering from diabetes or hypoglycemia, blacks out or loses awareness due to a lack of glucose to the brain. A medic alert bracelet can be an important life saving device for those with this risk factor. The amnesia, usually temporary, might contribute to a person's wandering from home and getting lost or disoriented.
Memory impairment that is not associated with brain damage is referred to as functional amnesia. Functional amnesia can be classified according to whether the amnesia is nonpathological or pathological. Nonpathological functional amnesia is a normal memory loss for events occurring during infancy and early childhood, sleep, hypnosis, and anesthesia. Pathological functional amnesia is an abnormal memory loss found in cases of functional retrograde amnesia and multiple personality. In contrast to neurological amnesia, pathological functional amnesia is usually associated with more severe retrograde than anterograde amnesia.
Both terms are used to categorize patterns of symptoms, rather than to indicate a particular cause or 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/declarative 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 for the few days following the accident (anterograde amnesia).
Discrete damage to the brain, especially to parts of the interior surface of the temporal lobes of the cerebral hemispheres, can also cause profound anterograde amnesia. The classical example of this devastating condition is the patient known by his initials, H. M., who underwent surgery to remove the inner parts of the temporal lobe on both sides, to relieve intractable epilepsy, and has subsequently suffered deep amnesia for decades. This part of the brain includes specialized regions of cerebral cortex called the hippocampus and the amygdala, which are thought to be involved in the laying down of memories. Unfortunately, this vital part of the brain seems to be particularly vulnerable: It is relatively easily damaged by hypoxia (for instance during surgical operations in which blood supply to the brain is compromised), by the degenerative changes that occur in Alzheimer's disease, and by infection in herpes simplex encephalitis. All of these conditions can produce pronounced amnesia.
This form of amnesia is distinct in that abnormalities in the hippocampus can sometimes be visualized using a special form of magnetic resonance imaging of the brain known as diffusion-weighted imaging (DWI). Symptoms typically last for less than a day and there is often no clear precipitating factor nor any other neurological deficits. The cause of this syndrome is not clear, hypotheses include transient reduced blood flow, possible seizure or an atypical type of migraine. Patients are typically amnestic of events more than a few minutes in the past, though immediate recall is usually preserved.
The vast majority of amnesic patients are chronic alcoholics, suffering from Korsakoff's syndrome.
Dissociative amnesia is a type of amnesia that is classified as a dissociative disorder. A dissociative disorder is a type of mental illness that involves a breakdown or disruption in the memory process. Dissociative amnesia occurs when a person blocks out certain information, usually associated with a stressful or traumatic event, leaving him or her unable to remember important personal information. With this disorder, the degree of memory loss goes beyond normal forgetfulness and includes gaps in memory for long periods of time or of memories involving the traumatic event.
Dissociative amnesia is not the same as simple amnesia, which involves a loss of information from the memory, usually as the result of disease or injury to the brain. With dissociative amnesia, the memories still exist but are deeply buried within the person’s mind and cannot be recalled. However, the memories might resurface on their own or after being triggered by something in the person’s surroundings.
Dissociative amnesia has been linked to overwhelming stress, which might be the result of traumatic events. Its frequency in the general population can be seen during periods of war or or at the time of natural disasters. While it cannot be treated with medication it can be treated in the same way that other mental illness are: Through psychotherapy, cognitive therapy, or family therapy.
Some types of amnesia, such as transient global amnesia, are completely resolved and there is no permanent loss of memory. Others, such as Korsakoff syndrome, associated with prolonged alcohol abuse or amnesias caused by severe brain injury, may be permanent.
Depending on the degree of amnesia and its cause, victims may be able to lead relatively normal lives. Amnesiacs can learn through therapy to rely on other memory systems to compensate for what is lost. Medications or other medical treatment cannot restore memory loss in amnesia. In severe cases, a person with amnesia needs to live in a supervised setting.
Eye Movement Desensitization and Reprocessing (EMDR) is a tool used in certain forms of psychotherapy in order to relieve the symptoms of post-traumatic stress disorder (PTSD). Repressed memories can resurface through this kind of work and should only be undertaken by a skilled therapist.
The root cause of most cases of amnesia is brain injury which is often times preventable through the avoidance of excessive alcohol use; the wearing of a helmet when bicycling or skateboarding, and by wearing a seat belt when driving. Brain infections should be treated quickly and aggressively and immediate medical treatment should be administered in the case of stroke or brain aneurysm.
Clive Wearing, a British musician and musicologist reportedly has the worst case of amnesia ever recorded. His memory span lasts a few seconds before it washes away in the blink of an eye and starts anew. It was triggered by a case of herpes encephalitis, which infects the brain and causes it to swell.
The encephalitis eroded Wearing's ability to make new memories, severing any recollection of the recent past. According to a The New Yorker magazine profile on him, something as simple as eating an apple would seem almost like a magic trick in Wearing's mind. One moment, he holds a whole apple in his hand. The next, there's nothing left but the core.
Unlike most amnesia cases in which older memories are preserved, much of Wearing's long-term episodic memory of specific facts and events disappeared. His motor skills and general intelligence remain intact; it's the memory of using them that's disconnected. For instance, Wearing still plays the piano proficiently, but he wouldn't remember doing so, much less what song he played.
Amnesia is prevalent in many works of fiction, such as in author Robert Ludlum's Bourne series, in which the main character, Jason Bourne, suffers from retrograde amnesia. Other modern films dealing with the subject include Eternal Sunshine of the Spotless Mind, Mulholland Dr., Memento, Vanilla Sky, and 50 First Dates.
Global amnesia is a common motif in fiction despite being extraordinarily rare in reality.
In movies and television, particularly sitcoms, it is often depicted that a second hit to the head (similar to the first one) cures the amnesia. In reality, however, repetitive concussions may cause cumulative deficits including cognitive problems, and in extremely rare cases may even cause deadly swelling of the brain associated with second-impact syndrome.
Recent research of fictional works from the 20th century shows that, though hardly anyone gets Amnesia in reality, over two percent of all fictional characters in movies, books, short stories and television shows (particularly soap operas) have had Amnesic effects at some point in their lives.
Famed mystery novelist Agatha Christie's disappearance due to purported amnesia caused an international stir in 1926. The author, who refused to comment on her supposed amnesia, claimed it was precipitated by traumatic events in her personal life. Her reticence about the matter created endless speculation in the press that it was merely a hoax.
While the incidence of amnesia affects only a small percent of the world's population, it's study is becoming increasingly important with the rising numbers of people with Alzheimer's Disease. Alzheimer's is expected to strike 34 million people globally by 2025 and 14 million in the U.S. alone over the next 40 years. Half of all people who reach age 85 will exhibit symptoms of the disease.
Early signs of amnesia can act as a precursor to Alzheimer's Disease or mild cognitive impairment. Both are forms of dementia, which produces memory loss along with the loss of cognitive skills. The hippocampus begins to malfunction early in Alzheimer's disease. Imaging studies have shown that people with Alzheimer's typically have smaller than average hippocampi.
New research suggests people with amnesia are marooned in the present, as helpless at imagining future experiences as they are at retrieving old ones.
The new study, reported in the January 2007 The Proceedings of the National Academy of Sciences, is the first rigorous test of how brain-injured people with amnesia mentally inhabit imaginary scenes. The results suggest that to the brain, remembered experience and imagined experience are reflections from the same mirror, rich inner worlds animated by almost identical neural networks.
The findings provide a glimpse into what it might mean to truly live in the moment. And they feed a continuing debate about memory. Some researchers say that the brain region central to forming new memories—the hippocampus, a sliver of tissue deep in the brain where the day’s memories are registered—is not necessary for retrieving those experiences, once they have been consolidated elsewhere in the brain.
Others, including the authors of the new study, contend that the hippocampus in fact provides the stage on which inner mental dramas are set. Without its help only the props remain—loose facts, people’s names, snippets from favorite songs: The players without the play.
"The study suggests that these patients have fragments, the brick and mortar to create new scenarios, but their descriptions lack coherence because they don’t have the scaffolding the hippocampus provides,” said Morris Moscovitch, a neuroscientist at the University of Toronto.
"We think that what the hippocampus provides is a scaffold for experience and imagination, and that scaffold is spatial," said Dr. Eleanor Maguire of University College London. The brain’s record of physical space, she said, appears to be necessary to infuse a scene with rich personal dimension.
In an essay also published in January 2007, in the journal, Nature, two Harvard researchers, Daniel L. Schacter and Donna Rose Addis, contend that this ability to richly imagine scenes, whether entirely dependent on the hippocampus or not, is perhaps the most promising frontier for memory research.
"For almost 100 years, memory has been the object of experimental studies that have focused almost exclusively on its role in preserving and recovering the past," they wrote. "We think it’s time to try to understand some of memory’s errors by looking to the future."
All links retrieved September 29, 2012.
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