Amnesia refers to the loss or injury of memory. It usually results from damage to parts of the brain vital for memory storage, processing, or recall (specifically, the limbic system, including the hippocampus in the medial temporal lobe). However, it can also be caused by serious psychological trauma. Amnesia can also be a symptom of neurodegenerative diseases. When the primary symptom of a patient is memory loss, the amnesiac (the person with amnesia) typically retains their sense of self. They may even be aware that they suffer from a memory disorder.
Various degrees of amnesia can occur. A mild concussion often only causes a patient to forget recent events in their lives, and that forgetfulness may only last a couple of hours. However, a patient who has suffered a serious head injury, for instance in an automobile accident, may have permanent memory loss and may be unable to learn new information. In most cases, the severe amnesiac will regain the memory of former capabilities such as the ability to use language and perform mathematical calculations.
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 the Wernicke-Korsakoff syndrome, for example, damage to the 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 has no consistently identifiable cause, but researchers have suggested that migraines or transient ischemic attacks may be the trigger. (A transient ischemic attack is sometimes called a small stroke.) In this third type of amnesia, a victim experiences sudden confusion and forgetfulness. Attacks can be as brief as 30 to 60 minutes or can last up to 24 hours. In severe attacks, a person is completely disoriented and may experience 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 exams may 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, and avoiding 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 immediate medical treatment.