Out-of-body 2

In August I posted an item on Blanke’s experiments with out-of-body experiences (here). Since then Anil Ananthaswamy has a article in the New Scientist on the subject. (here).

Out-of-body experiences are usually associated with epilepsy, migraines, strokes, brain tumours, drug use and even near-death experiences. .. (but) … about 5 per cent of healthy people have one at some point in their lives….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. … 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. … 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?

From various experiments, the area of the brain responsible seems to be the temporoparietal junction (TPJ).

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.

The TPJ is active when people imagine they are in a position different from their actual orientation.

This does not, however, explain the most striking feature of out-of-body experiences. “It’s a great puzzle why people, from their out-of-body locations, visualise not only their bodies but things around them, such as other people,” says Brugger. “Where does this information come from?”…(in) circumstances you are conscious of a sensation of movement, yet your brain is aware that your body cannot move. In an attempt to resolve this sensory conflict, the brain cuts the sense of self loose . “It resolves by splitting the self from its body,” says Cheyne. “The self seems to go with the movement and the body gets left behind.” Perhaps similar sensory conflicts cause classic out-of-body experiences.

Metzinger does have a suggestion. Imagine an episode from a recent holiday. Do you visualise it from a first-person perspective, or from a third-person perspective with yourself in the scene? Surprisingly, most of us do the latter. “In encoding visual memories, the brain already uses an external perspective,” says Metzinger. “We don’t know much about why and how, but if something is extracted from such a database [during an out-of-body experience], there may be material for seeing oneself from the outside.” … To address that question, Metzinger has teamed up with Blanke and his colleagues in an experiment that induces an out-of-body experience in healthy volunteers. They film each volunteer from behind and project the image into a head-mounted display worn by the volunteer so that they see an image of themselves standing about 2 metres in front. The experimenters then stroke the volunteer’s back – which the volunteers see being done to their virtual self. This creates sensory conflict, and many reported feeling their sense of self migrating out of their physical bodies and towards the virtual one.

Interestingly people claim to have seen themselves and others around them in the area while they had their eyes closed through the whole experience. So it is likely that the experience is created from bits of memories.

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