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Swiss neuroscientist Peter Brugger of the University Hospital in Zürich has come up with a new theory on "ghosts" and "doppelgängers". (A doppelgänger is the ghost of a living person, usually the viewer.) Brugger, whose idea is detailed in an upcoming edition of New Scientist magazine, thinks the viewer is experiencing a "phantom of the entire body" just in the same way an amputee might experience a "phantom limb". The limb is no longer there, but the brain still tells the amputee it is. Brain damage can cause this effect, but people with normal brains may have the effect triggered by intense emotions such as fear, sadness, or euphoria. Brugger reports that mountain climbers who have experienced oxygen deprivation at about 27,000 feet (8,200 m) have reported feeling a "presence" or having an out-of-body experience.
In September 2005, a team of mainly Swiss neuroscientists, including Brugger, reported the finding that they could trigger out-of-body experiences in subjects by stimulating a part of the brain.
- Olaf Blanke et al.: Linking out-of-body experience and self processing to mental own-body imagery at the temporoparietal junction. The Journal of Neuroscience, January 19, 2005, 25(3):550-557; doi:10.1523/JNEUROSCI.2612-04.2005. 
- Peter Brugger, "From Haunted Brain to Haunted Science: A Cognitive Neuroscience View of Paranormal and Pseudoscientific Thought," Hauntings and Poltergeists: Multidisciplinary Perspectives, edited by J. Houran and R. Lange (North Carolina: McFarland & Company, Inc. Publishers, 2001)
- P Brugger, SS Kollias, RM Müri, G Crelier, M-C Hepp-Reymond, M Regard. "Beyond re-membering: phantom sensations of congenitally absent limbs." Proceedings of the National Academy of Sciences of the USA (2000) 97, pp. 6167–6172.
- P Brugger, "Reflective mirrors: perspective transformation in autoscopic phenomena" Cognitive Neuropsychiatry (2002) 7, pp. 179–194.
- P Brugger, M Regard, T Landis, "Illusory reduplication of one's own body: phenomenology and classification of autoscopic phenomena." Cognitive Neuropsychiatry (1997) 2, pp. 19–38.