Seeing Impostors: When Loved Ones Suddenly Aren't Two different patients. Two different stories. But a shared delusion. Each is convinced that someone they love dearly is >not that person, but an impostor. A curious disorder known as Capgras delusion involves the distinct feeling that the people around you have been replaced. And no one is certain what causes it.

Seeing Impostors: When Loved Ones Suddenly Aren't

Seeing Impostors: When Loved Ones Suddenly Aren't

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Magritte's 1964 painting The Intimate Newspaper gets us thinking: Who is this? A familiar friend or a complete stranger? Rene Magritte/Corbis hide caption

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Rene Magritte/Corbis

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In the classic 1956 film Invasion of the Body Snatchers, the residents of a fictional town in California are beset by the feeling that their friends and family have been replaced by impostors. In the movie, this apparent delusion is not delusional at all: The townspeople are in fact being replaced -- by aliens, no less.

Numerous sci-fi films since have capitalized on our fear of being surrounded by duplicates -- replicas who look just like our loved ones but are not. And while there have so far been no confirmed cases of a human being replaced by an alien or any other life-form, the feeling that your loved one has been replaced by someone else can be very real.

Consider these two true stories:

A 37-year-old woman came into the office of Carol Berman, a psychiatrist at New York University Medical Center, with a strange complaint. She had returned to her house recently to find a man sitting on her couch. He was familiar, sort of, and he was wearing her husband's clothes. But something didn't feel right to this woman. She felt a strange kind of emptiness when she looked at him. She was struck by the very deep sense that her husband had somehow been replaced by this strange man.

A student at the University of California, San Diego was severely injured in a car accident. After several weeks in a coma, he regained consciousness and seemed to be doing fine. But according to V.S. Ramachandran, a neuroscientist at the university, when the patient's mother came to see him, he exclaimed, "Who is this woman? She looks just like my mother, but she's an impostor! She's some other woman pretending to be my mother."

Rare Delusional Disorder

Both patients, it turns out, were suffering from a rare delusional disorder, called Capgras. Capgras delusion can be brought about by a variety of conditions -- changes in brain chemistry associated with different mental illnesses, or physical trauma to the brain -- but the delusion always involves the distinct feeling that the people around you have been replaced by impostors. While they may look and act just like the real person, some essence of the person is missing, almost as though "the soul of the person isn't in there," Berman says.

Capgras delusion was first identified by French psychiatrist Joseph Capgras. In a 1923 paper, he wrote about a patient, "Madame M," who for 10 years had been "transforming everyone in her entourage, even those closest to her, such as her husband and daughter, into various and numerous doubles." Courtesy of Douwe Draaisma hide caption

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Courtesy of Douwe Draaisma

Currently, no one is certain of the underlying cause of Capgras, and there are different ways of explaining what is happening to these people. According to Berman, Capgras might be caused by psychological dissonance. There are usually things about the people close to us that we don't like. Normally, we combine these things with the parts we do like and develop a general emotional response to the whole person. But in some extreme cases, a change in character or a newly noticed behavior can just be too difficult to accept, to integrate into the whole. And so, rather than reframing our sense of who that person is, our brain just says: "That must not really be him."

Ramachandran thinks that Capgras can be better explained by a structural problem in the brain. According to Ramachandran, when we see someone we know, a part of our brain called the fusiform gyrus identifies the face: "That looks like mom!" That message is then sent to the amygdala, the part of our brains that activates the emotions we associate with that person. In patients experiencing Capgras, Ramachandran says, the connection between visual recognition and emotional recognition is severed. Thus the patient is left with a convincing face -- "That looks like mom!" -- but none of the accompanying feelings about his mother.

That's Not My Mother

Ramachandran holds that we are so dependent on our emotional reactions to the world around us, that the emotional feeling "that's not my mother" wins out over the visual perception that it is. The compromise worked out by the brain is that your mother was somehow replaced, and this impostor is part of a malevolent scheme.

Ramachandran thinks there's good evidence for this explanation of Capgras, in part because of an odd quirk in his patient's behavior. When his mother calls him on the phone and he hears her voice, he instantly recognizes her. Yet if she walks in the room after that call, he is again convinced that she is an impostor.

Why? Ramachandran says that our visual system and auditory system have different connections to the amygdala, so while the auditory recognition triggers an emotional response in his patient, visual recognition does not.

Treating The Illness

Capgras is very rare, and little is known about how to treat it. Those who have been afflicted with Capgras due to physical brain trauma may eventually re-establish the connection between perception and emotion. (Ramachandran's patient, for example, eventually recovered from his delusion.) And patients who experience Capgras alongside other mental disorders may be helped by medication. But for many Capgras patients, there is no treatment, and no amount of talk or reasoning can cure them.

While the feeling that the people around you have been replaced by impostors is certainly terrifying to imagine, the effect on the supposed impostor can be devastating, too. Carol Berman's husband began suffering Capgras after the onset of a particular kind of dementia in which neural transmission between different parts of the brain decays. Some days he knows that Berman is his wife. But other days, the woman who walks through the door is an impostor.

"I hope he's recognizing me," says Berman, "but you never know what you're going to get when you get back home."

Produced by Soren Wheeler