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.
Because many areas of the brain are involved in memory, damage almost anywhere in the brain can cause amnesia.
How amnesia is caused is only partly understood.
How long memory loss lasts depends on the severity of the damage that caused it.
Doctors evaluate memory loss by asking simple questions and doing formal tests of memory.
The cause of memory loss is treated if possible.
Memory loss can be classified as follows:
Memory loss involves facts more commonly than learned skills.
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.
Processing of memories involves the following:
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. For example, the hippocampus, located deep within the brain, is involved in the formation of new memories and retrieval of stored memories. The hippocampus is part of the limbic system, which controls the experience and expression of emotions. Thus, the hippocampus helps connect memories to the emotions experienced when the memories form.
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, damage almost anywhere in the brain can result in amnesia.
How amnesia is caused is only partly understood. It may result from
Depending on the cause, amnesia may be
Depending on the severity of the damage, amnesias can last for minutes, hours, or longer. Sometimes memory is lost suddenly but temporarily (called 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. Results of this evaluation and the person's symptoms often suggest a cause and other tests that may need to be done.