There have been many movies in Hollywood that focus on instances of amnesia. Some movies, in fact, use amnesia as the main plot device, such as the movie Memento, 50 First Dates, and Clean Slate. But amnesia can be defined in a few different ways.
The typical, or more well-known, form of amnesia is called retrograde amnesia. This is when after a specific event, someone has difficulty remembering past memories. For example, after a horrible car accident that causes a head injury, someone may have difficulty recalling memories from their childhood, or perhaps anything at all that happened before the accident. This means that their long-term memory has been altered. However, if they have problems remembering things that happen after the fact, and have difficulty with forgetfulness and bad short-term memory recollections, then they deal with what’s called anterograde amnesia.
Retrograde amnesia can be caused by a variety of reasons, but typically it is from an injury to the head. Some sort of trauma to the area of the brain that deals with storing long-term memories will cause retrograde amnesia. This form of amnesia can be either permanent or temporary. If caused by an injury, it can sometimes be temporarily caused by swelling around the brain due to the trauma. After the swelling goes down, memory begins to return back to the patient. This is not always the case, though, and there have been numerous cases where the damage is permanent and the information that was stored is lost forever with no chance of being recalled in the future.