In recent years, neuroscientists have examined the phenomenon of out-of-body experiences to better understand how the brain integrates sensory information to form the idea of self and the idea that the self is localized within the body (see Out-of-body but in the Brain, BrainWork, July-August 2006). New research furthers these findings by using special displays to induce the illusion of an out-of-body experience in normal participants.
“The interesting thing about out-of-body experiences is that they tell you something about the concept of self, that the self is usually located in your body,” says Sebastian Dieguez, a doctoral student and researcher in Olaf Blanke’s laboratory at the Brain-Mind Institute in Lausanne, Switzerland. “When your brain is working smoothly, you are inside your body and you are the author of what your body does. This is helpful for survival and for interacting with other people and the world.”
Previous research in brain-damaged individuals has demonstrated that damage to the temporal-parietal junction in the brain’s right hemisphere can lead to the feeling of being separate from one’s body. Researchers believe that problems with integrating sensory information lead to this inability for the brain to produce a seamless sense of self.
To try to induce an out-of-body experience, both Blanke’s research team and Henrik Ehrsson and colleagues at University College London (Ehrsson has since moved to the Karolinska Institute in Stockholm) used head-mounted displays, devices that project stereoscopic computer- or camera-generated images in front of the eyes, to perpetuate an extension of the rubber hand illusion. This old parlor trick, which creates the illusion that a visible fake hand is being touched rather than the person’s real, obscured hand, has been studied extensively by neuroscientists in the past decade to understand how the brain may be processing inconsistent sensory information.
“The idea was to see if we could do this to the whole body, if we could extend the illusion to the whole body, and then to try to measure the phenomenon if indeed we could do it,” says Dieguez. Both Blanke’s and Ehrsson’s teams’ findings appeared in the August 24, 2007, issue of the journal Science.
I SEE, THEREFORE I AM
Ehrsson’s group displayed video images of each participant so that they saw themselves sitting in the middle of the room from a few meters behind. As the participants watched, they saw a probe moving toward the image of their body on the camera while they were physically touched on the chest in such a way that could not be seen on the head-mounted display. This mismatched visual and tactile information led participants to feel as if they were sitting in a different part of the room, detached from their physical selves.
“It elicited a strong illusion, a vivid illusion, that one’s perceived self moved outside the physical body,” Ehrsson says. To test the strength of the illusion, Ehrsson’s group used the same setup, only this time they threatened the illusory body with a hammer while measuring galvanic skin response, which measures fear.
“People flinched and got very stressed,” Ehrsson says. “When we threatened the real body, though, they weren’t as nervous. This shows that their perceived self had moved to the location of the cameras.”
Blanke’s group used a similar methodology with a larger number of controls and a self-location measure instead of the emotional one that Ehrsson’s group used. Again, participants reported feeling as though their feeling of self location had shifted.
APPLYING SENSE OF SELF
Dieguez argues that these studies are merely the first step to truly understanding how the brain helps to create a sense of self, and, of course, where brain processes may break down leading to out-of-body experiences.
With greater knowledge, both research teams foresee potential clinical and technological applications. Ehrsson believes that being able to manipulate the perceived body may be of benefit to those suffering from body dysmorphic disorder, which often underlies eating disorders and involves perceiving the body to be larger or more distorted than it actually is.
“One could imagine using virtual technology to help people actually change the size of their perceived body,” says Ehrsson. “This could be used as a diagnostic tool or perhaps even a treatment to help individuals get a more realistic body image.”
Dieguez states that people with different neurological and psychiatric disorders could also benefit. “If we can play around with the body and its location in space, maybe we can train patients who have disorders that make it difficult for them to locate their own body to actually do so,” he says.
Technology enthusiasts also are following Blanke’s and Ehrsson’s work with interest. Understanding the neurobiological processes underlying out-of-body experiences might help make video games and virtual reality environments better.
“In the field of virtual reality, there is this notion of ‘presence,’ or the feeling that you are actually inside the environment,” Dieguez says. “It’s hard to measure this. But if we can help understand the idea of self-localization better, we can develop new methods to make these games and applications more realistic.”
But he cautions that those ideas are preliminary and that much work remains. Future studies in Blanke’s lab will examine modulating the feeling of being out-of-body, strengthening that feeling and attempting to induce it in different bodily positions.
“All of this is kind of new and developing,” Dieguez says. “We have only taken the first steps, I think.”