Interpreting the Film Memento
Part 1: Neuroscience Background
There appears to be a sizable cult following of Christopher Nolan’s 2000 neo-noir psychological thriller film, Memento, and rightly so. However, even though the film has many enthusiastic fans, few have completely unwrapped its intricate plotline. That is due in part to the fact that technical background information derived from Behavioral Neuroscience and Clinical Psychology are required to fully understand what is going on in the film. I have prepared a series of four articles, of which this is the first, that will discuss, and place in context, some of that necessary background information.
Short-Term and Long-Term Memory
The main character in Memento, Leonard, states numerous times that he has a memory problem. At one point in the film, he makes a more specific claim, that his problem involves short-term memory. Leonard is clearly wrong when he makes that specific assertion. (I will discuss the reasons he makes false claims such as this one in a later article in this series.). In actual fact, all of Leonard’s symptoms revealed in the film are ones that are related to long-term memory.
Memory refers to our capacity to retain and later retrieve information about our prior experiences. As we go about our daily lives, detailed information is being picked up and processed by our sense organs. However, we do not store all of these details in our memories. Only a tiny fraction of what we experience gets stored.
Scientific theories of memory sometimes make reference to a three-box model of memory systems. The basic idea is that memories are stored in three distinct neural systems (boxes) that operate sequentially. The first box is a sensory-memory system involved in the immediate storage of the vast amount of information flowing into the brain from our sense organs (what we see, hear, touch, taste, and smell). Most of this information is typically lost within a second or two.
However, a few items of information that were initially stored in sensory memory are transferred into a second box, short-term memory, where they can be held for about 30 seconds, after which they fade away unless they are rehearsed. An example would be when you look up someone’s telephone number and have to remember it long enough to dial the number. If the time from when you look it up until you actually dial the number is more than about 30 seconds, then the only way to retain this number in your short-term memory is to repeat it to yourself over and over.
Most short-term memories fade and are lost, but a few get transferred into a third box, the long-term memory system, where they can be stored (semi)permanently. These stored, long-term memories constitute what you remember about your past.
The memory problem exhibited by the character Leonard in Memento is not related to problems with the operation of his sensory or short-term memory systems. Instead, the problem has to do with his inability to form new long-term memories.
Types of Long-Term Memory
There are two qualitatively different kinds of long-term memories stored in the brain, sometimes referred to by the technical terms declarative memories and procedural memories.
Declarative memories are what we are usually referring to when we use the term memories. They reflect explicit facts that we can remember based on our past experiences. Declarative memories come in two types, called semantic and episodic. Semantic memories are facts we have stored, irrespective of whether or not we can remember when or where we learned those facts. An example of a semantic memory would be that I have stored the fact that a dog is a small mammal with fur. Episodic memories are autobiographical memories of the events in our own lives. For example, I remember that when I was five years old I had a dog named spot.
Procedural memories involve knowing how to do things. An example would be remembering how to ride a bike. Suppose that you had visited your grandfather’s house when you were 5 years old, and during that visit, he taught you how to ride a bike. You are now an adult, and you no longer remember having been taught to ride a bike by your grandfather (an episodic memory) or even the fact that you know how to ride a bike (a semantic memory). Nevertheless, if for some reason you find yourself sitting on a bike, you will probably be able to ride it. This is because the motor skill of knowing how to ride a bike has been stored as procedural memory.
Declarative memories and procedural memories can be dissociated in some patients with brain damage. Patients with damage to certain regions of the brain have deficits that involve declarative memories, but procedural memories are unaffected, and vice versa.
Retrograde and Anterograde Amnesia
Amnesia is a clinical condition in which a patient has abnormal gaps in memory. Two major types are called retrograde and anterograde.
Retrograde amnesia is the type best known in popular culture, and most frequently depicted in films. The onset of retrograde amnesia is typically attributed to some traumatic event, either a physical event such as a blow to the head, or psychological such as being witness to some horrific event. The deficit is in the form of an inability to retrieve memories of what happened during certain periods before the traumatic event, thus the term retrograde.
Anterograde amnesia is rarer and involves loss of the ability to form new memories about events that happen after the trauma. One of the most intensely studied subjects in the history of behavioral neuroscience is referred to in the scientific literature as subject HM. He suffered from an amnesic disorder characterized technically by the term anterograde long-term declarative memory loss. His amnesia was the result of damage that was localized to an area in and around the hippocampus in the medial temporal lobe of the brain. He could remember events that occurred prior to his brain damage but was unable to form new long-term declarative memories for events that happened after the brain damage. However, parts of his brain outside of the area near the hippocampus were unaffected so he retained some ability to form new long-term procedural memories.
The type of memory loss exhibited by the actual patient HM provides the prototype for the memory loss that is displayed by the fictional character, Leonard, in the movie Memento. (And also by a second character, Sammy. Much more about that in later postings.)
Leonard’s memory problem is that he has been unable to form new long-term declarative memories since an accident that happened to him at the same time his wife was murdered. As a result, Leonard cannot remember new facts (semantic memories) that he learns during his investigation of the circumstances that led to the murder of his wife, nor can he remember new events that happen to him during the investigation (episodic memories).
Leonard attempts to overcome these memory deficits by creating a written record of notes that can serve the function of being his “memory.” He still has a functioning short-term memory system so as long as he rehearses what he has just experienced or learned, he retains the ability to create a record of that information in his notes, some of which he later has transferred to tattoos on his own body.
And Leonard takes advantage of his intact ability to form new long-term procedural memories (Leonard refers to these as “habits”) to create a system that allows him to access the information stored in his written notes. Leonard, through repetition, established the following habit; Whenever he is in an environmental condition in which he is confused, a motor action kicks in that causes him to examine his arm for the presence of a tattoo. This habit will bring some information into his (still functioning) short-term memory. That information can now direct Leonard to do something else such as, get a note from his pocket and read it. By chaining together in his short-term memory the information in the notes, Leonard is able to bootstrap himself towards accomplishing his goals. And his system is quite powerful since one of the activities Leonard can engage in during this goal-driven activity is to write new notes and store them for use the next time his habit is elicited.
The system Leonard has worked out is a stretch in terms of real-world plausibility. It is not really feasible that someone with a total lack of ability to form new declarative memories, such as Leonard, could actually function and live on his own based on a strategy that uses only “habits.” Nevertheless, if we are willing to give the film a certain amount of poetic license, it is possible to imagine that a system along the lines of the one used by Leonard could facilitate his goal of trying to solve the mystery of who murdered his wife. That quest forms the primary plotline of the film.
In my next (upcoming) article on this same topic, I will explain how the director and screenwriter, Christopher Nolan, was able to structure the film in ways that amplify some of these basic neuroscience findings of memory loss, including an intermixing of black-and-white and color-coded scenes.
Ron Boothe
psyrgb@emory.edu
My other articles on this topic can be found here:
