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| Illustration: Byron Eggenschwiler |
About two months after his younger brother died of complications from HIV, Chris—a friend of mine in his 50s living in California—woke up early one morning. He got off the bed, stood up, stretched, turned around and got the fright of his life.
“The shock was electric,” Chris told me last year. “Because I was still lying in the bed sleeping, and it was very clearly me lying there sleeping, my first thought was that I had died.”
Of course, Chris hadn’t died. He was having what neuropsychologists call a doppelgänger experience: He found himself inhabiting an illusory body while his real, physical body was lying in bed. He says he’s not clear how long the feeling lasted. Eventually, “there was this enormous sucking sensation,” said Chris, making a long, drawn-out slurping sound. “I felt like I was dragged, almost thrown, back into the bed, smack into myself.” He woke up screaming.
Doppelgängers are the stuff of literature, found in unsettling stories by authors from Edgar Allan Poe to Guy de Maupassant. Modern neuroscientists call the doppelgänger effect an autoscopic phenomenon (from “autoscopy”; in Greek, autos means “self,” and skopeo means “looking at”), in which a person may hallucinate that they are seeing and even interacting with another “me”—a visual double.
Probably the most widely experienced and best-known form of these autoscopic phenomena is the out-of-body experience, in which people often report leaving their physical body and looking down at it from above.
Unnerving as they can be, out-of-body experiences, doppelgänger phenomena and other autoscopic hallucinations are probably our best window onto the way our brain constructs our sense of self, starting with the bodily self. Having a bodily self means several things. At its most fundamental, it anchors you in a body that feels like it is yours. You also feel that your body occupies a certain volume in physical space and that you are within that volume looking out with a perspective that feels like your own.
But as Chris’s experience shows, there are times—albeit rare—when we aren’t anchored in our physical body, suggesting that there is something malleable about the way our brains construct our bodily selves.
Over the years, scientists have found other examples of such malleability. Take the rubber-hand illusion—written up in the journal Nature in 1998 by Matthew Botvinick and Jonathan Cohen—in which an experimenter strokes a subject’s real hand with a brush while simultaneously stroking a rubber hand. The subject can see only the rubber hand, not the real hand, which is obscured by a screen.
In most people, something crazy happens within a couple of minutes: Instead of feeling the touch of the brush on the real hand, you begin to feel the touch at the location of the rubber hand. It is as if your brain takes ownership of the rubber hand.
So what is happening here? The brain has to make sense of conflicting information: sensations of brush strokes on the real hand and the sight of a rubber hand being stroked. So the brain, in effect, decides that the eyes don’t lie: The rubber hand must be the source of the sensations, and so the brain proceeds to embody the inanimate hand.
To create a sense of embodiment, the brain relies on incoming sensations—both from the outside and from inside the body—to construct maps of the body and body parts. We perceive these maps as our bodily selves.
Over the past decade, two teams—one led by Olaf Blanke at the Ecole Polytechnique Fédérale in Lausanne, Switzerland, and the other by Henrik Ehrsson at the Karolinska Institute in Stockholm, Sweden—have demonstrated full-body versions of the rubber-hand illusion. Just as our brain can take “ownership” of a rubber hand, it can also be fooled—using more elaborate experimental setups—into taking ownership of a mannequin’s body or even a virtual body.
These experiments show us that, to create the bodily self, the brain has to integrate various sensations—such as touch, vision and many other types of internal and external information. There is no one place in the brain where this integration happens. Rather, researchers have identified a whole host of regions that are involved. The various illusions arise when the brain is fed conflicting information and tries to make the sense of it.
One can even fool the brain into embodying empty space. For example, in the rubber-hand illusion, if the experimenter takes the rubber hand away and instead moves the brush in the air in a manner suggestive of having a hand there while simultaneously stroking the hidden real hand, some people will soon start feeling touch in empty space. I can attest to this: I was taken aback by the weirdness of this illusion when I experienced it in Dr. Ehrsson’s lab.
The brain’s process of sensory integration can be fooled not just in the lab but in real life too—leading to, for example, the doppelgänger experience. If the brain’s processes are working correctly, there should be just one representation of the body in the brain. But sometimes the process goes awry, leading to two representations, and the brain has to choose the representation in which to anchor the self—and sometimes it chooses one, sometimes the other. This is what neuroscientists now think leads to the doppelgänger effect.
Such hallucinations can make people feel that they have a “soul” or something incorporeal that can leave the physical body. This leads to a kind of dualism—the view that the stuff of the body and the stuff of the mind are distinct and different.
But what these lab experiments and studies are showing us is that nothing is really leaving the body during an out-of-body experience. When the brain is operating on sensory information that is congruent (meaning that the sensations of touch match what the eyes are seeing, for example), the brain situates the self in the body and provides a sense of perspective and body ownership.
But when the sensations aren’t congruent, because someone is being tricked by the rubber-hand illusion or suffering from some neurological aberration, the brain does its best to make sense of all the misleading data. The brain can miscalculate the coordinates for the self, positioning it outside the body or in another illusory body.
So modern studies of out-of-body experiences and full-body illusions aren’t making a case for dualism. Rather, they’re showing us that the sense of bodily self is something that is constructed by the brain moment by moment. The bodily self turns out to be the basis for our greater sense of self, which involves more complex aspects including the narrative self (that is, the stories we tell others and ourselves about who we are) and the social, cultural self.
Our sense of self arises from a complex interaction among brain, body, mind and culture—and in the full-blown selves we are, all aspects of the self interact with and influence one another. But it all begins with the body.
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