Loss of memory due to brain damage caused by either injury or the degeneration of brain cells as a result of dementia or infection.  It is subdivided into three categories, each differing in cause and symptoms.  Anteriograde amnesia is often caused by brain trauma and presents itself as the inability to lay down new memories acquired after the trauma.  Recall of recent events and short term memory are poor, but events prior to the trauma are recalled with clarity.  Conversely, retrograde amnesia is inability to recall events that occurred prior to the trauma.  Retrograde and anteriograde amnesia can occur in the same patient.  Transient global amnesia is assumed to be caused by ischemia, a temporary loss of blood supply to the brain.  It can last anywhere from an hour to a day, and patients lose all memory of recent events, and have difficulty remembering new information. 

Depending on the cause of amnesia, the brain may be able to recover many of its previously lost functions, or may get worse.  Amnesia associated with neuronal death is likely to be irreversible.  Amnesia caused by brain injury may see some improvement over time, as the brain attempts to heal itself.  However, when amnesia is caused by a neurodegenerative disorder such as Alzheimer’s, improvement is unlikely.

Treatment varies with the type of amnesia, and is often very case specific.  Cognitive rehabilitation helps patients learn strategies to cope with their memory loss, such as keeping a memory notebook or putting reminder notes around the house, and relearning to concentrate.