I only recently came across an issue of the "New Scientist" magazine number 2729, dated 10 Oct 2009 pp34-36, which carried an article by Anil Ananthaswamy titled "The mind unshackled."
The article is a review of current scientific theory on the out-of-body experience.
"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 doppelganger experience: you sense the presence 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 doppelganger...Finally, your self leaves your body altogether and observes it from outside..."
In 2002, Olaf Blanke performed surgery on a woman with severe epilepsy, and while stimulating the temporoparietal junction (TPI) , found that she experienced an OBE. "The TPI processs 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. " Your sense of self.
In 2007, Dirk de Ridder implanted electrodes near a patient's TPI in an attempt to cure the patient's tinnitus. The patient experienced something close to an OBE. "...he would feel his self shift about 50 centimetres behind and to the left of his body..." A PET scan was able to be taken and showed that the TPI was "...activated during the experiences."
This is very interesting research and implies that in some medical conditions, an OBE may be generated by itself, with no external stimulation. I look forward to reading further research findings along these lines.