Amnesia is a popular theme for many movies and television shows. Characters often appear with no identity and no memories of the past. They are essentially starting over, but they, for the most part, are fully equipped mentally to do so. However, this cinematic portrayal has little in common with the reality of amnesia.

In the movies: The amnesia may be unrelated to any abnormality or injury of the brain. People just forget. The reason may be unclear. Sometimes sleep seems to wipe the memory clean of the previous day’s events—an improbable scenario but full of comic possibility. Or the cause may be a blow to the head, a head injury in a crash of some sort, or a psychologic trauma, such as witnessing a murder or being raped. Or memories may be removed by a special erasing device, as used in Men in Black or Eternal Sunshine of the Spotless Mind.

In reality: Amnesia usually has less glamorous causes, such as a brain infection, alcoholism, a stroke, drugs, a brain tumor, or an injury due to brain surgery. Psychologic trauma occasionally causes amnesia—a disorder called dissociative amnesia. However, psychologic trauma often has the opposite effect on memory loss. People cannot forget what happened to them. They frequently replay and relive the traumatic event, even though they would rather forget it.

In the movies: People with amnesia have few if any problems with everyday activities. They may readily get a new job and make new (or new-old) friends.

In reality: Most people have great difficulty learning and retaining new information (because the brain has been damaged). As a result, they struggle with everyday activities. People have difficulty remembering names and where they are going and why. These problems cause frustration, and people with amnesia often feel very confused and get lost.

In the movies: People often go through a complete personality change. Values and behaviors are transformed. Bad people become good.

In reality: Amnesia affects personality or identity only rarely, when the specific areas of the brain that controls these functions malfunction.

In the movies: People with amnesia due to trauma have stored memories of the trauma, intact and accurate, deep in their unconscious. With the right trigger, they can replay the memories of the trauma like a video camera.

In reality: The way the brain recalls memories is dynamic. When people remember an event, they reconstruct it, pulling bits from different places in the brain. No memory, traumatic or otherwise, is ever frozen and immune from reconstruction over time.

In the movies: Amnesia can be cured mechanically. That is, amnesia caused by a blow to the head can often be reversed by another blow. Or amnesia, regardless of its cause, can be cured by looking at a familiar object or by being hypnotized.

In reality: Most of these cures are dubious. A second blow to the head is more likely to cause further damage. Hypnosis is useful only when the cause of amnesia is a disturbing event. Then, when done gently and carefully, it is often successful. Treatment and its chances of success depend on the cause.

In the movies: Memories are not really lost, just temporarily inaccessible.

In reality: Whether memories can be recovered depends on the severity and cause of the damage. Often, the damage is not severe, or the cause is temporary. In such cases, the amnesia often lasts for only minutes or hours, and most people recover their memory without treatment. However, when damage is substantial, memory often cannot be recovered.