learning

MEMORY

Disorders

A loss of memory, or amnesia, can be caused by an injury to the head. A condition called traumatic automatism, in which a person functions normally but afterward remembers nothing, sometimes results from an injury. More severe injuries can produce a confused state called anterograde amnesia in which new memories cannot be stored. Retrograde amnesia may also occur in which memories prior to the injury are lost. The amnesia from electroconvulsive, or shock, therapy mimics that of head injuries. (See also Amnesia.)

Amnesia caused by organic disease is usually more severe. In a condition known as Korsakoff's syndrome, amnesia can be severe enough to produce a moment-to-moment existence in which new information never progresses beyond immediate memory. Encephalitis, or inflammation of the brain, can cause a similar type of amnesia. Memory defects after brain surgery are common. In these cases memory often returns slowly, sometimes years later.

Memory failure was once thought to be a normal process of aging, but studies of the elderly indicate that it is the result of some disease process. Severely impaired memory in the elderly is generally classified as either senile dementia (senility) or Alzheimer's disease. (See also Aging.)

Memory loss that occurs without injury or disease is termed psychogenic amnesia. It can be induced during hypnosis so that events that occur during a hypnotic trance are forgotten (see Hypnosis). Hysterical amnesia, or dissociation, is a state in which a specific memory cannot be recalled except under hypnosis or in dreams. It is frequently a neurotic reaction in which painful or frightening memories are repressed. (See also Psychology.)

The term paramnesia is used to describe memory errors. Simple memory deception occurs when dreams, fantasies, or hallucinations are remembered as real events. The sensation that a new event has occurred before is called deja vu, from the French, meaning "already seen." It is believed that deja vu originates from some partly forgotten memory.

Confabulation is the recall of false memories resulting from organic brain disease. A person suffering from confabulation will often report in great detail events that never occurred, apparently with no awareness that the memories are false.

A greatly heightened memory is termed hypermnesia. A person with photographic memory stores information in highly visual, detailed, persistent, and vivid terms. A true photographic memory is apparently rare.

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