Forget What You Heard About Amnesia - Medical Myths - Harvard Commentaries

Sometimes you hear or see something so many times, you think it must be true. But while watching a movie, "The Majestic," I was reminded how wrong that can be. In the movie, the main character, played by Jim Carey, survives a terrible automobile accident and loses all memory. He's otherwise fine, but as a result of his trauma, he can't recall his name, his job, his relationships — it's all gone.

It's a remarkably common device for fictional plots in books, television and movies — "Desperately Seeking Susan" also comes to mind — and in many cases, the character with amnesia has a second injury that prompts his or her recovery. It may make for good entertainment, but it's unlikely you have ever known someone to experience this sort of problem because it rarely (if ever) happens that way. Certainly amnesia doesn't require another blow to the head to resolve.

The word “amnesia” means loss of memory. But, because memory formation and brain function are complex, there are many types of amnesia. For example, memory can be divided into:

Immediate — Recalling information a few seconds after learning it
Short-term — Recalling recently learned information minutes or more after presentation
Long-term — Memory of remote events occurring months or years ago

A distinction also can be made between procedural memory (recalling how to do something, such as riding a bicycle), and declarative memory (recalling past information or experiences). Finally, researchers recognize additional types of memory including semantic (information that is independent of time, such as vocabulary), episodic (information tied to a particular time, such as recalling one's wedding day), and prospective(remembering that an event in the future will occur, such as bringing change for the bus fare).

One's identity is among the most durable long-term memories — forgetting who you are is rare, especially without other significant neurological and/or psychiatric illness. In “The Majestic,” the amnesiac can't recall anything about himself or recent events and struggles to play the piano, illustrating that he'd lost not only all remote long-term memory, but procedural memory as well. Remarkably, his immediate recall seems normal, as he's able to remember the names and faces of people he meets after his accident without difficulty. This situation is highly unusual in real life.

Researchers have discovered that different parts of the brain are important for forming and storing different types of memory. For example, several areas of the brain called the limbic system are important in memory storage. Injury to both the right and left sides of the limbic system is usually necessary to cause amnesia, but if injury is greater on the right, visual memories may be lost while the left side of the brain is more involved with verbal information.

Anterograde amnesia — The most common type of amnesia, it is characterized by difficulty forming new memories, a particular problem in dementing illnesses such as Alzheimer's disease.

Retrograde amnesia — This involves loss of past memories, involving those from a few seconds to a few months ago; it most commonly follows head injury and tends to improve over time.

Transient global amnesia — A temporary loss of all memory, but it particularly affects the ability to form new memories (severe anterograde amnesia), with milder loss of past memories (retrograde amnesia) going back a few hours. It's rare and most common among older persons with vascular disease. A study published in June 2004 shed light on why brain scans are often normal in people with this type of amnesia: Abnormalities may not show up right away. Researchers found that it can take a day or two for abnormalities in the memory-forming portions of the brain to show up. These findings suggest that impaired blood supply, as may occur with a stroke, is to blame. This form of memory loss typically goes away entirely within hours.

Almost any disease or injury to the brain can affect memory. The most common are Alzheimer's disease and other dementias, stroke, trauma or seizures. Amnesia is a common, initial symptom of Alzheimer's disease or related disorders. Some people with amnesia suffer from psychiatric illness — so-called psychogenic amnesia; in those circumstances, loss of past memories and identity may be prominent despite normal ability to learn and remember new information.

Although head injuries are common and may be serious, head trauma leading to complete and persistent loss of memory of past events, including one’s identity, is extremely rare. When amnesia follows head trauma, it most often follows a concussion or more severe injury and typically affects past memories (that is, the amnesia is retrograde). A host of other problems may be caused by head injuries that cause amnesia, ranging in seriousness from life-threatening skull fractures, bleeding around or into the brain, or swelling of the brain, to self-limited symptoms such as headache, fatigue or dizziness. When amnesia is prominent, many of these other symptoms are often present. Recovery of memory usually parallels resolution of these other problems.

Many, perhaps most, head injuries can be prevented by wearing protective headgear (for example, during athletic activities, or while riding a bicycle or motorcycle), not driving after drinking alcoholic beverages, and taking appropriate precautions when working in high places.

The Bottom Line

The movies are often not the best place to get medically accurate information. Recognize that head injury is a common problem, but sudden, complete and persistent memory loss is not. Enjoy the movies, but take the medical events you see on the screen with a grain of salt (and popcorn).

Robert H. Shmerling, M.D., is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.