Amnesia is a loss of memory that most commonly results from a medical condition (e.g., a blow to the head) or the use of certain substances (e.g., drugs, alcohol). Less frequently it may be related to severe emotional trauma. People who have amnesia are unable to recall certain past events or information they previously have learned or have trouble forming new memories.

Memory is a process that occurs when the brain records and stores recollections of important information, events and people. Memory is divided into immediate memory (events that happened in the previous few seconds), intermediate memory (events that happened in the preceding few seconds to the last few days) and long-term memory (events that happened further back in time).

Despite this process of recording information, most people forget things from time to time. Amnesia is a more serious form of memory loss that causes significant impairment to a person’s ability to interact socially or to perform job-related tasks. A person with amnesia may lose the ability to recall large portions of memory.

In most cases, amnesia is temporary and lasts from only a few minutes to several hours before disappearing on its own. However, some forms of damage to the brain can result in amnesia that is permanent.