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:
Retrograde: Amnesia for the events before the event that caused the amnesia
Anterograde: Amnesia for the events after the event that caused the amnesia
Sense-specific: Amnesia for events processed by one sense, such as hearing
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:
Taking in new information (registration)
Linking new information with memories already stored in the brain, with mental pictures, or with other things that can help with retrieval (encoding)
Recalling the memory (retrieval)
The brain’s mechanisms for storing information and recalling it from memory are located primarily in the temporal lobe Temporal lobe damage Because different areas of the brain control specific functions, the location of brain damage determines the type of dysfunction that results. Which side of the brain is affected is also important... read more and frontal lobe Frontal lobe damage Because different areas of the brain control specific functions, the location of brain damage determines the type of dysfunction that results. Which side of the brain is affected is also important... read more , 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 Limbic Lobe Because different areas of the brain control specific functions, the location of brain damage determines the type of dysfunction that results. Which side of the brain is affected is also important... read more , 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 parts 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.
Causes of Amnesia
How amnesia is caused is only partly understood. It may result from
A nutritional disorder, particularly thiamin deficiency Thiamin Deficiency Thiamin deficiency (causing beriberi and other problems) is most common among people whose diet mainly consists of white rice or highly processed carbohydrates in developing countries and among... read more , which can cause Wernicke-Korsakoff syndrome Wernicke-Korsakoff Syndrome Wernicke-Korsakoff syndrome is an unusual form of amnesia that combines two disorders: an acute confusional state (Wernicke encephalopathy) and a type of long-term amnesia called Korsakoff syndrome... read more
Disorders that reduce the supply of blood or nutrients to the brain (including strokes Ischemic Stroke An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke... read more
and cardiac arrest Cardiac Arrest and CPR Cardiac arrest is when the heart stops pumping blood and oxygen to the brain and other organs and tissues. Sometimes a person can be revived after cardiac arrest, particularly if treatment is... read more 
)Use of certain drugs (such as some antidepressants, muscle relaxants, or opioids, as well as amphotericin B or lithium Lithium In bipolar disorder (formerly called manic-depressive illness), episodes of depression alternate with episodes of mania or a less severe form of mania called hypomania. Mania is characterized... read more )
Depending on the cause, amnesia may be
Temporary, as occurs after head injury
Permanent and unchanging (as occurs after a serious disorder such as encephalitis or a stroke that affects a large part of the brain)
Progressive (as occurs with disorders that cause progressive degeneration of the brain, such as Alzheimer disease)
Symptoms of Amnesia
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 Transient Global Amnesia Transient global amnesia is a sudden, temporary loss of memory for events during, after, and sometimes before the event that caused the amnesia. What causes transient global amnesia is not known... read more ).
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.
Diagnosis of Amnesia
A doctor's evaluation
Formal tests of memory
Doctors evaluate memory loss by asking simple questions (such as repeating a list of three items) and by doing formal tests of memory What the doctor does Memory loss can be a symptom of brain malfunction. It is one of the most common reasons that people, particularly older people, visit a doctor. Sometimes family members notice and report the... read more . Results of this evaluation and the person's symptoms often suggest a cause and other tests that may need to be done.
Treatment of Amnesia
Treatment of the cause if possible
If a cause of amnesia is identified, it is treated if possible. Such treatment may or may not lessen the amnesia.
