Rachel Nuwer in Smithsonian Magazine:
A tickle on the back of your neck, a sudden feeling that you are not alone: some believers in the paranormal attribute these sensations to the presence of a ghost, angel or otherworldly being.
Now, a team of Swiss neuroscientists have figured out how to conjure those spirits—or at least the perception of them—in the lab. The sensation of an otherworldly presence, they found, actually derives from garbled sensorimotor brain signals, in which a person's self awareness of their own body is projected into a seemingly disconnected space. In such cases, the researchers explained in a release, the brain mis-assigns its own life signals as belonging to someone or something else.
The team first studied the brains of a dozen patients who all suffered from such apparitions—a common symptom for people with some forms of epilepsy, schizophrenia or other neurological disorders. MRI analyses showed that they all had abnormal activity in three regions of the brain involved in self-awareness, movement and proprioception (the sense of one's position in space), the researchers reported.
Next, they attempted to recreate this neurological experience in healthy volunteers.