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Amnesia am-ˈnē-zhə

By Juebin Huang, MD, PhD

Amnesia is total or partial loss of the ability to recall experiences or events that happened in the preceding few seconds, in the preceding few days, or further back in time.

Memory loss may involve events that occurred just before the cause of the amnesia (retrograde amnesia) or just after (anterograde amnesia). How far back in time memories are lost varies from a few seconds before the amnesia occurred to a few days, to further back in time, affecting more distant past (remote, or long-term) memories.

The brain’s mechanisms for storing information and recalling it from memory are located primarily in the temporal and frontal lobes, but many areas of the brain are involved in memory. Emotions originating from the limbic system can influence the storing of memories and their retrieval. The limbic system includes part of the cerebrum and some structures deep within the brain. Areas that are responsible for alertness and awareness in the brain stem also contribute to memory. Because memory involves many interwoven brain functions, virtually any type of brain damage can result in amnesia.

How amnesia is caused is only partly understood. It may result from

  • A nutritional disorder, particularly thiamin deficiency

  • A head injury

  • Disorders that reduce the supply of blood or nutrients to the brain (including strokes, seizures, and migraines)

  • A brain infection (encephalitis)

  • Dementia

  • Chronic alcohol abuse

  • A brain tumor

  • Severe mental stress

  • Use of certain drugs (such as amphotericin B or lithium)

Depending on the severity of the damage, most amnesias last for only minutes or hours. Sometimes memory is lost suddenly but temporarily (called transient global amnesia—see Transient Global Amnesia). Some people recover their memory without treatment. However, if brain damage is severe, the ability to form new memories may be lost. Affected people are more likely to remember things from the distant past. For example, people may remember their spouse from their first marriage but not the current marriage.

Doctors evaluate memory loss by asking simple questions (such as repeating a list of three items) and by doing formal tests of memory (see What the doctor does). Results of this evaluation and the person's symptoms often suggest a cause and other tests that may need to be done.

If a cause is identified, it is treated if possible. Such treatment may or may not lessen the amnesia.

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