Amnesia refers to the loss of memory. Memory loss may result from damage to parts of the brain vital for memory storage, processing, or recall (the limbicsystem, including the hippocampus in the medial temporal lobe). Amnesia canalso be a symptom of neurodegenerative diseases. People whose primary symptomis memory loss (amnesiacs), typically retain their sense of self. They may even be aware that they suffer from a memory disorder.

Amnesia has several root causes. Most are traceable to brain injury related to physical trauma, disease, infection, drug and alcohol abuse, or reduced blood flow to the brain. In Wernicke-Korsakoff syndrome, for example, damage tothe memory centers of the brain results from the use of alcohol or malnutrition. Infections that damage brain tissue, including encephalitis and herpes, can also cause amnesia. If the amnesia is thought to be of psychological origin, it is termed psychogenic. There are at least three general types of amnesia.

Anterograde amnesia follows brain trauma and is characterized by the inability to remember new information. Recent experiences and short-term memory disappear, but victims can easily recall events prior to the trauma. Retrograde amnesia is the opposite of anterograde amnesia: the victim can recall events that occurred after a trauma, but cannot remember previously familiar information from before the trauma. Transient global amnesia hasno consistently identifiable cause, but researchers have suggested that migraines or transient ischemic attacks may be the trigger. (A transient ischemicattack is sometimes called a small stroke.) A victim experiences sudden confusion and forgetfulness. Attacks can be as brief as 30-60 minutes or can lastup to 24 hours. In severe attacks, a person is completely disoriented and mayexperience retrograde amnesia that extends back several years.

In diagnosing amnesia, doctors look at several factors. During a physical examination, the doctor inquires about recent traumas or illnesses, drug and medication history, and checks the patient's general health. Psychological examsmay be ordered to determine the extent of amnesia and the memory system affected. The doctor may also order imaging tests such as magnetic resonance imaging (MRI) to reveal whether the brain has been damaged, and blood work to exclude treatable metabolic causes or chemical imbalances.

Treatment depends on the root cause of amnesia and is handled on an individual basis. Regardless of cause, cognitive rehabilitation may be helpful in learning strategies to cope with memory impairment.

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.

Amnesia is only preventable in so far as brain injury can be prevented or minimized. Common sense approaches include wearing a helmet when bicycling or participating in potentially dangerous sports, using automobile seat belts, andavoiding excessive alcohol or drug use. Brain infections should be treated swiftly and aggressively to minimize the damage due to swelling. Victims of strokes, brain aneurysms, and transient ischemic attacks should seek immediatemedical treatment.

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