Dramatic structure is the basic form in which a presentation is set up. It includes elements like theme, action, crisis, and climax. Basically, it is the way that the author/playwright sets up the action of the piece of theatre.
Memento is a psychological mystery about a very confused, desperate man named Leonard Shelby who has lost his short-term memory. Piece by piece he is trying to reassemble the bits and pieces of his life, to re-create the mess that his life now is. But each couple of minutes, he forgets everything again.
In this film, director, Christopher Nolan, chose two very specific dramatic forms to help tell his story. The first form was that the action of the film moved backwards in non-sequential order. The beginning is the end and the end is the beginning. The second dramatic form that he used was that he had two individual plots going at the same time. There are individual scenes in black and white that play in between the color scenes. The monochromatic scenes move forward. At the end of the film, when Leonard kills James, the black and white and the color scenes come together to form the last couple of minutes in the movie. I believe that Nolan used these specific structures for a variety of reasons.
Leonard Shelby is living a condition in this film that no one could possibly understand. In an effort to bring the audience into Leonard's world, make them feel what he feels, Nolan uses the specific dramatic structures that I mentioned earlier. At the beginning of the film, the man at the hotel says, "Your life is all backwards; you remember what you want to do but you can't remember what you did." In Memento, the action occurs in frames, which move backwards. What ends up happening is that the audience forgets what happened in one frame when the next frame begins to play. In this way Christopher Nolan thrust us into Leonard's shoes and forced us to experience what he experienced every day.