Coding error can be explained as failure to engage information in your long term due to lack of concentration or failure to pay attention to the information presented. When I think about this particular theory, Leonard's photos come to mind. He has a photo of everything, from the sign of the motel he resides in to his car, instead of incorporating new memories. Decay theory is described as the process of losing memories that are not used and slowly leave our mind. Sometimes we are unable to remember something because we haven't thought about it. This theory explains why we can't remember exactly how to solve old high school math test problems years after graduating. We are not practicing these kinds of problems so we cannot remember them because they simply vanish. We also have the theory of interference. This can be caused when we are not focused on something and our attention is divided. Retroactive interference can be explained as “out with the old and in with the new”. Are you puzzled why you can't remember the old password on your computer because the new password is the one you forcefully remembered. This leads you to forget your oldest password in the process. There is an example of this type of interference found in the film when Leonard reaches for a pen trying to concentrate on writing down his argument with Natalie, but doesn't.