Christopher Nolan's screenplay was based on his brother Jonathan Nolan's story "Memento Mori." However, the screenplay is still considered original (rather than adapted), because Jonathan's story wasn't published until after the film was completed.
EASTER EGG: The Limited Edition DVD (and the standard Region 2 edition) allows the movie to be watched in the exact chronological order of the events in the film. The first couple of scenes of the regular cut of the movie appear normal in this version, meaning they are not reversed. However, this version of the movie on Disc 2 is quite difficult to reach (the user must answer several questions and solve a puzzle), and forward, reverse, and chapter skip capabilities are disabled.
During Teddy's line, "You don't have a clue, you freak!" Director Christopher Nolan felt that Joe Pantoliano (Teddy) did not quite nail the end of the line, so he decided to re-record the last two words to his liking, delivering them himself. Therefore, in the final film, the words, "you freak", as we hear them, are actually being said not by Pantoliano, but by Nolan impersonating Pantoliano's voice. Pantoliano was unaware of the dubbing, until an interview for Anatomy of a Scene: Memento (2001).
The medical condition experienced by Leonard in this film is a real condition called Anterograde Amnesia, the inability to form new memories after damage to the hippocampus. During the 1950s, doctors treated some forms of epilepsy by removing parts of the temporal lobe, resulting in the same memory problems.
Stephen Tobolowsky has stated that during his audition for Sammy, he had mentioned to Christopher Nolan that he had experienced amnesia personally. A few years earlier, he was given an experimental pain killer that induced amnesia for a surgery he had undergone. Tobolowsky said it may have helped him get the part, because no other actor would likely have had his first-hand experience.
The test given to Sammy Jankis (Stephen Tobolowsky), involving the electrified objects, is based on a real-life case study of a patient, commonly referred to as HM, who suffered from the same form of amnesia following surgery to treat severe epilepsy. A doctor repeatedly shook HM's hand with a joy buzzer, shocking him every time. After a few trials, HM refused to shake hands. The test, shown in the movie, is an illustration that Sammy's condition was not identical to a real-life case study, but would not have excluded him from insurance coverage.
"Paranoid Android" by Radiohead was originally going to be used in the closing credits, but Christopher Nolan decided that the royalties needed to use this song (owned by Capitol Records) would be too great for this low-budget film.
The address on Teddy's Driver's License has a non-existent zip code (94181) transposed from an actual San Francisco zip code 94118. The address number on Pine Street (an actual street in San Francisco) shown does not lie inside zip code 94118.
When we first see Leonard's map of the area, we can see two streets that have commonality with Blue Velvet (1986). There is a "Booth Street", the primary antagonist in Blue Velvet (1986) is Frank Booth. A second street, worthy of note, is "Lincoln Street", which Jeffrey is explicitly told to avoid, and where the apartment of Dorothy Vallens resides in Blue Velvet (1986). These are the only roads that are not nominally numerical, for example "Seventh Street".
The film's subject matter was conceived of when Christopher Nolan was joined by his brother Jonathan on a late summer cross-country road trip, as Christopher was moving to Los Angeles and Jonathan had time before returning to his studies at Georgetown to spend time with his brother and help with with the move. By the time they arrived in L.A., the entire screenplay had been stated out loud between the brothers.
Carrie-Anne Moss personally recommended Joe Pantoliano for the role of Teddy, having become good friends with him while they were working on "The Matrix". Christopher Nolan and his producers had reservations about this because they weren't sure Pantoliano's screen persona (often overtly villainous) was the right match for Teddy, but they met with him and decided his talent made him the right person for the part. Nolan later praised Pantoliano for having brought the right amount of subtlety to his performance as Teddy.
After Brad Pitt expressed interest in signing up to play Leonard but ultimately had to pass on the project due to other commitments, Christopher Nolan did not consider any other "A-list actors" because he realized that having a talented but lesser-known lead actor would allow for the film's budget to be more evenly distributed. That process led to Nolan nearly casting Aaron Eckhart in the role, and eventually giving the part to Guy Pearce.
The trivia items below may give away important plot points.
After his wife's death, Sammy (Stephen Tobolowsky) is shown sitting in a mental institution. Briefly, just after someone walks in front of him, and before the scene cuts back to Leonard (Guy Pearce) on the phone, Sammy is actually replaced by Leonard sitting in the same chair. This supports the conclusion, that the tragic end of Sammy's story, is actually an event from Leonard's own past, just as Teddy (Joe Pantoliano) later tries to convince him.
The picture of Leonard that he finds in the envelope under his motel door, shows him pointing at a bare spot on his chest. He tells Natalie that this spot is reserved for when he finds John G. Later, when Leonard is driving to the tattoo parlor, he thinks about his wife, and a flashback is shown in which he is lying in bed with his wife. The bare spot in this shot now contains, "I've done it."
While Leonard is watching television at Natalie's, a picture of a needle with a person wearing a white v-neck shirt in the background can be seen. In the story of Sammy Jankis, Sammy injects his wife with insulin while he watches television. This alludes to the possibility that Sammy Jankis' story is really Leonard's own. Moreover, the white v-neck in the background, is the same shirt that Leonard's wife wears in another scene.
During Leonard's third and final conversation with the anonymous caller, his fingers hover over the numbers 555-0134. This is Teddy's phone number, which is on the bottom of his photograph, thus hinting that Leonard is actually talking to Teddy.
Chronology: When numbering the scenes chronologically, then sorting them how they appear in the film, the pattern becomes more clear. The letters A-V will represent the color scenes (with A happening chronologically first, and V chronologically last), and the numbers 1-22 represent the black and white scenes chronologically. The scenes appear in the film like this: 1, V, 2, U, 3, T, 4, S, 5, R, 6, Q...20, C, 21, B, 22/A The two types of scenes alternate. The black and white scenes (numbers) start from the beginning, and work forward to the climax at 22/A, while the color scenes (letters) work backward from the climax at 22/A. The climax scene (22/A) changes to color halfway through, showing the convergence of the two story lines.
Jimmy G. is the name used by Dr. Oliver Sacks to refer to one of his patients in the book "The Man Who Mistook His Wife for a Hat." Jimmy G. suffers from retrograde and anterograde amnesia, and is incapable of forming new memories, just as Leonard is. Throughout the movie, Leonard is in search of a man whose name could be John or James G., and in fact, one of his victims is one such "Jimmy G."
The narrative jumps one hundred thirteen times, from one time period in the story to another. The first scene of the movie is the end of the story, and the story begins in the middle of the movie (when Leonard meets Sammy Jenkis).