What are you doing running through the streets in your underpants?” asks Tyler Durden in the movie Fight Club. “We both use that body.” He is addressing his unnamed doppelganger (German for “double walker”), whose life he has gradually usurped. The movie, a smash hit grossing $100 million, is just one recent example of our long-standing fascination with the idea of double selves, which stretches from ancient Egyptian and Norse mythology, through German folklore (in which it was considered a harbinger of death), into the hands of Edgar Allan Poe, Groucho Marx, and Brad Pitt.

Freud was one of the first to attempt to treat doppelgangers scientifically, calling them the “return of the repressed.” He argued that they are an aspect of the psyche that is out of control, and will persist until directly confronted and defeated. Modern science has taught us that, in one sense, he was right: Doppelgangers are the result of a fracture in the process by which we construct our identity.

In the fall of 2011, a 15-year-old girl came to the Department of Neurology at the University of Geneva suffering from seizures. She told Olaf Blanke, a neurology professor at the university, that during her seizures she saw her own double. Her visions happened during the aura stage—the initial stage of a seizure when patients are still conscious but their vision and senses begin to blur. First, the girl would feel nauseous and extremely warm, and then she would see a transparent body rising from her stomach. The body would shape itself into a mirror image of her own self and look back at her, giving her the impression that this was her “soul” leaving her body. As her seizure wound down, it would re-enter her body.

The girl was diagnosed with a lesion in her insular cortex, the part of the brain involved in perception, self-awareness, and regulating the body’s homeostasis. The brain generates our experience of self by merging information about our body from external sources such as the eyes, the ears, and the skin, and internal sources such as the heart and the stomach. Blanke and his colleague Lukas Heydrich, who examined her, say that such a lesion in the insular cortex prevents the brain from integrating the body’s external and internal perceptions, resulting in a corrupted sense of self. “We found that the system representing the internal and external bodily states is no longer in sync,” explains Heydrich. “The brain tries to solve this conflict by coming up by the most plausible explanation: a second self in the form of a doppelganger.”

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In a study1 in the journal Brain, Heydrich and Blanke noted that all of the epileptic patients they saw who reported seeing doubles also had a lesion in the insular cortex. Heydrich and Blanke’s research suggests that when lesions are surgically removed, doppelganger visions disappear. Other causes of doppelganger visions, however, are less understood. Schizophrenics, for example, also report seeing doubles, but the reasons behind these visions are not clear, in part due to lack of research. Such symptoms are usually treated with medication.

Blanke and his colleagues found that doppelgangers can also be induced. Blanke was able to evoke a vision of a double by stimulating patients’ temporoparietal junction, which integrates and processes inputs from the external environment and from within the body. “To a certain degree, we can induce something that resembles a doppelganger, e.g. a full body illusion,” Blanke says, although it wouldn’t be as strong of an experience as a full-blown hallucination.

Blanke’s colleagues Jane Aspell and Heydrich were able to make subjects identify with virtual avatars.2 The researchers flashed images of subjects’ bodies to them (which represented an external input) in synchrony with their heartbeats (which represented an internal input). After a few minutes, the subjects said they felt a stronger identification with their virtual body than their corporeal ones, and thought they were physically located where their avatars were—despite being 2 meters away from their avatars.

The coping aspect of doppelgangers could be used for therapy.

Seeing a vision of yourself might not just be a symptom of a disease, but potentially also an aspect—even if an extreme one—of the psychology of a healthy person. Polar explorer Ernest Shackleton spoke about seeing a doppelganger during a 36-hour march through the mountains and glaciers of the islands of South Georgia, referring to it as a “divine companion” who helped him cope with the journey’s hardships. When explorer Ann Bancroft was injured during her 1,900-mile journey through Antarctica, she found comfort in the presence of a doppelganger that was stronger than her, uninjured and walking alongside her with ease. “It was a good medicine, it was what I needed,” Bancroft later wrote.

The late psychologist Julian Jaynes echoed the view that doppelgangers are a coping mechanism when he said that their calming effects could be seen on “shipwrecked sailors who have conversations with an audible God for hours in the water until they were saved.” “From a medical point of view it makes sense,” Heydrich says. “Dissociation and depersonalization have always been a coping mechanism.”

The coping aspect of doppelgangers could be used for therapy. Blanke, for example, used a robotic device to stroke the backs of 30 volunteers. “As the robot strikes, the subject watches a virtual body receiving the same stroking pattern on its back,” Blanke explains. “The stronger they identified with their avatars, the more pain reduction they reported.” The technique could have applications for chronic pain sufferers.

“You could propose that because you identify with the virtual image, and dissociate from the physical body to a certain degree, the perception and the neural representation of the pain is diminished,” Heydrich says. “I am sure that one day people will be able to evoke ‘positive hallucinations’ to feel less pain or other unpleasant feelings…in a similar manner that people can be taught to meditate or use cognitive behavioral techniques to overcome fear.”

Fight Club ends with a battle to the death between Durden and his double, suggesting that only one can survive. But the reality of doppelgangers is more complex. Blanke decided to hold off on surgery on his 15-year-old patient until her brain was more fully developed. In the meantime, she said she was relieved that there was a medical explanation for her symptoms. What’s more, she had developed a strong affinity with her double. “It meant something special to her—a connection with a part of herself that was familiar and somewhat reassuring,” Blanke says.





David Levine (@Dlloydlevine) has written for Scientific American, the Los Angeles Times, Good Housekeeping, BioTechniques, and Robotic Trends. He is co-chairman of Science Writers in New York (SWINY).





References

1. Heydrich, L. & Blanke, O. Distinct illusory own-body perceptions casued by damage to posterior insula and extrastriate cortex. Brain 136, 790-803 (2013).

2. Aspell, J.E., Heydrich, L., Marillier, G., Lavanchy, T., Herbelin, B., & Blanke, O. Turning body and self inside out: visualized heartbeats alter bodily self-consciousness and tactile perception. Psychological Science 24, 2445-2453 (2013).