Amnesia

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Amnesia

Definition

Amnesia is a partial or total loss of memory.

There are numerous causes of amnesia, including stroke, injury to the brain, surgery, alcoholism, encephalitis (inflammation of the brain), and electroconvulsive therapy. (Electroconvulsive therapy, or ECT, is a treatment for various mental disorders in which electricity is sent to the brain through electrodes.)

Contrary to the popular notion of amnesia—in which a person suffers a severe blow to the head, for example, and cannot recall his or her past life and experiences—the principal symptom of amnesia is the inability to retain new information, beginning at the point at which the amnesia began. The capacity to recall past experiences may vary, depending on the severity of the amnesia.

There are two types of amnesia: retrograde and anterograde. Retrograde amnesia refers to the loss of memory of one’s past and can vary from person to person. Some sufferers retain virtually full recall of things that happened prior to the onset of amnesia; others forget only their recent past, and still others lose all memory of their past lives. Anterograde amnesia refers to the inability to recall events or facts introduced since the amnesia began.

The diagnostic manual used by clinicians, called the Diagnostic and Statistical Manual of Mental Disorders (DSM), lists three classifications of amnestic disorders , described below.

Amnestic disorder due to a general medical condition

The memory loss of amnestic disorder due to a general medical condition can be transient or chronic. This disorder can manifest as retrograde or anterograde loss. For diagnosis, the person must experience impairment of social or occupational functioning that differs from their normal levels, and the memory loss cannot occur as part of dementia or delirium. The medical condition responsible must be confirmed by patient history or by physical exam or lab results.

Substance-induced persisting amnestic disorder

Substance-induced persisting amnestic disorder can occur with use of alcohol, sedatives, hypnotics, or anxiolytics. Methotrexate, a chemotherapy drug, can induce it, as can some toxins, including lead, mercury, carbon monoxide, insecticides, or industrial solvents. There are subtypes, including alcohol-induced persisting amnestic disorder. In the alcohol-induced form, the symptoms of Wernicke-Korsakoff syndrome may manifest as a result of the thiamine deficiency. Full recovery is not the norm with alcohol-induced amnestic disorder but is possible when caused by other drugs. The diagnostic criteria for the substance-induced form of amnestic disorder are similar to those for that induced by a general medical condition, except that the history should show exposure to the substance involved.

Amnestic disorder not otherwise specified

If the characteristics of the amnesia do not fit either of the above categories, the disorder is then classified as amnestic disorder not otherwise specified, generally because the causative agent/event is not known.

Dissociative amnesia

Dissociative amnesia is part of a different group of disorders, the dissociative disorders. It manifests as an inability to remember information that is personally important, but possibly traumatic or stressful. It was previously called Psychogenic amnesia. The memory impairment in this disorder is reversible, and memory loss can be of several types. It can be localized, in which the missing memory covers a defined period of time, or it can be selective, so that only bits and pieces of a situation are recalled. There are also three less common types: generalized (memories covering a lifetime are missing); continuous (memories are missing from a specific time period up to the present); and systematized (only memories from specific categories of information are missing, such as the names of family members). This disorder can arise in a person of any age.

Amnesia is not always obvious to the casual observer—motor skills such as tying shoelaces and bike riding are retained, as is the ability to read and comprehend the meaning of words. Because of this phenomenon, researchers have suggested that there is more than one area of the brain used to store memory. General knowledge and perceptual skills may be stored in a memory separate from the one used to store personal facts.

Childhood amnesia, a term coined by Anna Freud in the late 1940s, refers to the fact that most people cannot recall childhood experiences during the first three to five years of life. It has been suggested that this type of amnesia occurs because children and adults organize memories in different ways. The differences are based on the brain’s physical development and communication among the different areas of the brain involved in developing memory. Others believe children begin remembering facts and events once they have accumulated enough experience to be able to relate experiences to each other.

Resources

BOOKS

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 4th ed., Text rev. Washington, D.C.: American Psychiatric Association, 2000.

OTHER

Martin, Peter R., Charles, K. Singleton, and Susanne Hiller-Sturmhoefel. National Institute of Alcohol Abuse and Alcoholism. “The Role of Thiamine Deficiency in Alcoholic Brain Disease.” <http://pubs.niaaa.nih.gov/publications/arh27-2/134-142.htm> (2006).

National Institute on Alcohol Abuse and Alcoholism. “Alcohol’s Damaging Effects on the Brain.” <http://pubs.niaaa.nih.gov/publications/aa63/aa63.htm>.

National Institute of Neurological Disorders and Stroke. “Wernicke-Korsakoff Syndrome Information Page.” <http://www.ninds.nih.gov/disorders/wernicke_korsakoff/wernicke-korsakoff.htm>.

Emily Jane Willingham, PhD

The Gale Encyclopedia of Mental Health