Amnesia is the condition in which a loss of mem­ory occurs and extended periods of time are for­gotten. People afflicted with amnesia experience difficulty accurately estimating time, sometimes even after a recovery in which they fully regain their lost memories. Symptomatically, amnesic patients typically underestimate the time they spend engrossed in any particular activity. They also overestimate time that has passed after a cer­tain activity ended. Even though they are coherent in their thought processes, amnesic and postamne­sic patients maintain difficulties in dating past events and in constructing frameworks of time.

These amnesic memory losses may result from many organic occurrences, or medical issues like brain injury or trauma, shock, fatigue, disease, infection, or illness. They may also be triggered by addictions to drugs or alcohol. Amnesias that are not organic or associated with a detectable injury or illness are usually called psychogenic amnesias. These memory losses can be caused by suggestion under hypnosis, or they may arise spontaneously as a result of psychological conflict or stress. This may also be a defense mechanism in which a vic­tim of amnesia represses unpleasant memories. Psychogenic memory losses are often reversible.

Organic memory disorders are the most fre­quently observed category of memory loss. These losses may be transitory, such as the loss of time and memory during or after binge drinking alcohol or experiencing an epileptic seizure. Memory losses that are more enduring are most often asso­ciated with brain disease or head injuries. There are three main types of organic amnesias: antero­grade, retrograde, and transient global. Anterograde amnesia is the loss of memory of events or time occurring after a trauma. A patient is unable to maintain and store memories of current events or new experiences after an organic episode. Retrograde amnesia occurs when the memories occurring immediately before a trauma or disease are forgotten. Posttraumatic or traumatic amnesia are posttraumatic confusional states that can last for several hours, days, or weeks after regaining consciousness or recovering from such traumas as a blow to the head. With severe or extensive retro­grade amnesia, a person afflicted can lose up to 20 years of memories prior to the trauma.

Alternately, psychogenic amnesias are not caused by physical injury or disease. The loss of personal memories, such as one’s identity or past personal experiences, is a psychogenic memory loss and is most often linked to a substantial emo­tional occurrence, acute conflict, or significantly stressful experience.

Hysterical amnesia is sometimes motivated by a patient’s need or desire to escape a traumatic or frightening event or series of events that had caused great conflict or anxiety. It is not linked to a phys­ical condition or medical disorder. This loss is also commonly referred to as repression or motivated forgetting. Although hysterical amnesia sometimes extends to forgetting school-based knowledge, such as reading, spelling, or arithmetic, this type of memory loss is most often related to dementia or organic conditions or injuries. Repressed memories can often be recovered through psychotherapy. Memories can also be lost if a hypnotist suggests to the hypnotized patient that he or she should not remember anything from the session. Hysterical amnesia has two main types: One involves a failure to recall particular past events, and the other type involves failure to register current events.

Some amnesic episodes last for extended peri­ods of time, during which people may begin new life patterns. They may wander away from home or work, leaving their life behind for hours, days, or weeks. When people recover from such periods, also called fugue states, they usually remember only the time previous to and occurring after this fugue state. The time and the events that occurred during the amnesic period or fugue state are entirely forgotten.

See also Consciousness; Diseases, Degenerative; Medicine,

History of; Memory

Further Readings

McGaugh, J. (2003). Memory and emotion. New York: Columbia University Press.

Ribot, R. (1882). Diseases of memory. New York: Appleton-Century-Crofts.

Schacter, D. (1996). Searching for memory: The brain, the mind and the past. New York: Basic Books.

Terr, L. (1994). Unchained memories: True stories of traumatic memories, lost and found. New York: Basic Books.

Thompson, R., & Madigan, S. (2005). Memory: The key to consciousness. Washington, DC: Joseph Henry Press.

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