Hollywood has a love affair with amnesia. Since the 1930s, this memory disorder has had a major or minor role in nearly 80 films. One of the most notable recent examples of a film showcasing amnesia is Memento (2001). It tells the story of a former insurance investigator, Leonard Shelby, and his attempts to track down the man who attacked him and his wife-killing her and leaving him with a brain injury that has destroyed his ability to form new memories.

In important ways, Memento depicts amnesia more accurately than any major film release to date. But it also contains a few notable errors, offering an opportunity to set the record straight on a much-misunderstood memory impairment.

Who am I?

Especially in comedies, characters often suffer from "amnesia" after being bopped on the head. Typically, the person regains consciousness with a puzzled expression and asks, "Who am I? Where am I? How did I get there?"

Memento perpetuates the myth that amnesia is marked by a loss of identity. In his travels, Shelby encounters a number of people to whom he must explain his "condition." He tells one of them, "I don't have amnesia. I know who I am. I just can't form new memories." Although people with amnesia do lose the ability to form memories-technically known as anterograde amnesia-they do not forget who they are.

There is, however, a rare psychological phenomenon associated with a loss of one's identity-so rare that some experts doubt that it even exists. It's called fugue state, defined in the textbooks as an "inability to recall one's past and assumption of a new identity, which may be partial or complete." Amnesia is about memory, not identity.

What is anterograde amnesia?

Leonard Shelby suffers from profound anterograde amnesia, which is depicted accurately in the film. The disorder is marked by an inability to create memories of facts and events. This is often referred to as declarative memory, consisting of what happened to you yesterday, the name of someone you met on the street, the town you just arrived in the previous day.

These are all examples of information that you recall and describe (declare). To make up for his loss of declarative memory, Shelby has facts essential to his investigation tattooed on his chest and snaps numerous Polaroid photos of important places he's been, people he has met, and things he has seen.

The memory bins

In explaining his condition, Shelby says he has "no short-term memory." That's true: Short-term memory is the bin in which we store recent experiences and perceptions for minutes to hours while they are "consolidated" into more enduring "long-term" memories.

But what Shelby does have is working memory: the bin that holds experiences for moments to seconds. That means he can hold a conversation-as long as the other person doesn't go on speaking for too long. In that case, Shelby might forget where the conversation started, and become confused. But like other people with anterograde amnesia, Shelby maintains his intelligence, his ability to reason, make logical arguments, express his thoughts, read a map, or keep a telephone number "in mind" long enough to dial it.

The ghost of Patient HM

Shelby's predicament is familiar to anyone acquainted with the famous case of "Patient HM." This man-his name is kept confidential to protect his privacy-lost his ability to form new memories in 1959. HM suffered from intractable epileptic seizures in a region of the brain called the medial-temporal lobes. To stop the dangerous electrical storms in HM's brain, surgeons removed part of his medial-temporal lobes where the storms originated.

In the process, HM lost two-thirds of his hippocampus, a pair of pinkie-sized structures that are critical to the formation of new memories. Like Leonard Shelby, patient HM wakes every day with no memory of what took place the day before. He has, however, maintained his older memories, those dating back to before his operation.

Injured memories

Unlike patient HM, Shelby acquired his anterograde amnesia through an accidental brain injury. This does happen, but it's much more common for people to develop anterograde amnesia from a stroke, viral encephalitis, chronic epilepsy, or the interruption of the brain's oxygen supply due to near-drowning or strangulation (hypoxia or anoxia). These all may result in damage to the hippocampus, which appears to be especially vulnerable to damage from oxygen starvation. While it is conceivable that a blow to the head could completely disable the hippocampus, it's not the way it usually happens in real life.

Losing the past: retrograde amnesia

Another plot point in Memento that doesn't quite ring true is his vivid memory of the physical attack in which he was injured. People with anterograde amnesia often cannot remember the trauma that caused their memory loss as well as some memories of events just before the trauma. Scientists theorize that this loss of past memories, or retrograde amnesia, occurs because harm to the hippocampus has disrupted the process of consolidation, by which recent memories are gradually transformed into enduring long-term memories. The combination of anterograde amnesia plus partial retrograde amnesia is quite common. Collectively, it's often known as simply "amnesia."

Following procedure

One form of memory left intact in both Patient HM and the fictional Shelby is the ability to learn skills. Called procedural memory, it's what allows us to learn how to ride a bike, play the piano, or swing a golf club properly. By performing sets of actions (procedures), the brain forms a kind of unconscious memory of the skills that you "just know how to do." Areas of the brain outside the medial-temporal lobes are involved in procedural memory, which is why an injury that results in anterograde amnesia doesn't affect procedural memory.

Procedural memory is central to a subplot in Memento in which Shelby flashes back to an insurance investigation he carried out before his injury on a man claiming amnesia. Shelby wanted to make sure the man wasn't "faking" his memory disorder. The man, Sammy, undergoes a test in which he receives a small electrical shock when he picks up a block of a certain shape. In the film, Sammy repeatedly picks up the electrified block, suggesting that his mind does not respond to what Shelby calls "conditioning."

Even if he had amnesia, Sammy would typically associate something negative with the shock block and avoid touching it, even though he might not have been able to articulate exactly why. But Sammy does not appear to have procedural memory. Shelby concluded that Sammy's memory loss must have been psychological in nature, not the result of a physical brain injury.

There is such a thing as psychological, or "psychogenic," memory loss. In response to a traumatic event-witnessing the death of a loved one, being attacked-some people may "block out" memory of the event as a coping mechanism. This usually resolves with time and perhaps psychotherapy.

Faking it

Real psychologists use a test for procedural memory to distinguish between people with real amnesia and people who may be pretending to have it. Fortunately it doesn't involve electric shocks-understandably, a practice not allowed in real scientific research. The test subject is given a list of words to read. Then after a short delay, the tester asks the subject to recall the words. A person with amnesia (or pretending to have amnesia) would naturally be unable to remember the words accurately.

Then, the person is shown another list-one in which some of the words from the previous list are intermixed with new words-and asked if he recognizes any of them. A person with anterograde amnesia will have poor word recall but will have near-normal recognition of words seen previously.

Hollywood vs. Reality

To be fair, amnesia is often no more than a secondary plot device in films, used to set up a mystery and draw the viewer in. But in the real world, it's a rare and fascinating disorder that has taught scientists much about the workings of human memory. For all its minor technical mistakes, Memento is a high point in the history of amnesia in film-if for no other reason that it shows so dramatically the devastating effect of losing one's ability to remember even the most mundane events of daily life.

FURTHER READING:

Coping with Mild Traumatic Brain Injury, by Diane Roberts Stoler and Barbara Albers Hill. (Avery Penguin Putnam, 1998 (paperback), 284 pp., $14.95).

This manual explains the diagnosis, treatment, and rehabilitation of brain-injured people and offers practical suggestions for coping with physical and emotional consequences of brain injuries.

Brain Injury Association
105 N. Alfred Street
Alexandria VA 22314
800-444-6443
www.biausa.org
See the BIA's series of seven brochures, "The Road to Rehabilitation,"
available free by request or on the organization's website.