Out of your head: Leaving the body behind

So what exactly is an out-of-body experience? A definition has recently emerged that involves a set of increasingly bizarre perceptions. The least severe of these is a doppelgänger experience: you sense the presence of or see a person you know to be yourself, though you remain rooted in your own body. This often progresses to stage 2, where your sense of self moves back and forth between your real body and your doppelgänger. This was what Brugger's young patient experienced. Finally, your self leaves your body altogether and observes it from outside, often an elevated position such as the ceiling. "This split is the most striking feature of an out-of-body experience," says Olaf Blanke, a neurologist at the Swiss Federal Institute of Technology in Lausanne.

Some out-of-body experiences involve just one of these stages; some all three, in progression. Bizarrely, many people who have one report it as a pleasant experience. So what could be going on in the brain to create such a seemingly impossible sensation?

The first substantial clues came in 2002, when Blanke's team stumbled across a way to induce a full-blown out-of-body experience. They were performing exploratory brain surgery on a 43-year-old woman with severe epilepsy to determine which part of her brain to remove in order to cure her. When they stimulated a region near the back of the brain called the temporoparietal junction (TPJ), the woman reported that she was floating above her own body and looking down on herself.

This makes some kind of neurological sense. The TPJ processes visual and touch signals, balance and spatial information from the inner ear, and the proprioceptive sensations from joints, tendons and muscles that tell us where our body parts are in relation to one another. Its job is to meld these together to create a feeling of embodiment: a sense of where your body is, and where it ends and the rest of the world begins. Blanke and colleagues hypothesised that out-of-body experiences arise when, for whatever reason, the TPJ fails to do this properly (Nature, vol 419, p 269).

More evidence later emerged that a malfunctioning TPJ was at the heart of the out-of-body experience. In 2007, for example, Dirk De Ridder of University Hospital Antwerp in Belgium was trying to help a 63-year-old man with intractable tinnitus. In a last-ditch attempt to silence the ringing in his ears, Ridder's team implanted electrodes near the patient's TPJ. It did not cure his tinnitus, but it did lead to him experiencing something close to an out-of-body experience: he would feel his self shift about 50 centimetres behind and to the left of his body. The feeling would last more than 15 seconds, long enough to carry out PET scans of his brain. Sure enough, the team found that the TPJ was activated during the experiences.

Insights from neurological disorders or brain surgery can only take you so far, however, not least because cases are rare. Larger-scale studies are required, and to achieve this Blanke and others have used a technique called "own-body transformation tasks" to force the brain to do things that it seemingly does during an out-of-body experience. In these experiments, subjects are shown a sequence of brief glimpses of cartoon figures wearing a glove on one hand. Some of the figures face the subject, others have their back turned (see diagram). The task is to imagine yourself in the position of the cartoon figure in order to work out which hand the glove is on. To do this, you may have to mentally rotate you own body as one image succeeds another.

As volunteers performed these tasks, the researchers mapped their brain activity with an EEG and found that the TPJ was activated when the volunteers imagined themselves in a position different from their actual orientation - an out-of-body position .... read more