This one has few practical implications, but it is interesting nonetheless. Amnesia is often used as a convenient plot device in films and TV, where people suddenly lose all memory of their names or the past lives. This can happen – it’s called a fugue state, but it’s very rare. The film Memento has a more accurate portrayal of amnesia, or at least the variant known as “anterograde amnesia”. As in the film, people with this condition lose the ability to entrench new memories, losing new information and experiences after a short space of time. But even in this film, the hero loses a sense of his own identity, something that happens very rarely in real life.

People can also suffer from “retrograde amnesia”, where they lose older memories, particularly those that happened immediately before an accident or injury. It typically occurs alongside anterograde amnesia, and is rarer as a stand-alone condition.