There's a scientific reason why you may feel the presence of ghosts.
A lot of us have had the sense that there's someone behind us, and yet when we turn, nobody else is in the room. To researchers, that's called a feeling of presence, or FoP. It can happen to anyone, although it particularly afflicts people with Alzheimer's disease and schizophrenia.
A team of scientists in Switzerland was able to replicate that FoP in healthy individuals. As explained in a paper published this month in Current Biology, they used a robot that pokes individuals in the backs and managed to trigger the feeling in some test subjects that several other people were in the room, even though there was only the robot.
Professor Olaf Blanke and his team at the Swiss Federal Institute of Technology in Lausanne were seeking a better understanding of neurological disorders with their experiment. But the results are also intriguing for the many mentally healthy people who believe they have felt the presence of ghosts.
Blanke told HuffPost Weird News that the study indicates that sometimes "healthy subjects can experience the same hallucinations as patients suffering from schizophrenia have."
"Hallucinations are quite frequent in the general population," said Blanke, a neurologist and neuroscientist. "These data and ours on FoP suggest that there is no clear-cut differences between health and disease but rather a quasi-continuous spectrum."
The scientists in Switzerland first examined 12 patients who had suffered brain damage from epilepsy, stroke or other conditions and who reported having feelings of presence. Brain scans revealed lesions in their frontoparietal cortexes, the area of the brain that is aware of the "self," according to Scientific American.
"When the patient was standing, the presence was standing," the scientists reported in Current Biology, describing the patients' FoPs. "When the patient was sitting, the presence was sitting. When the patient was moving, the presence was moving."
The scientists then tested whether they could trigger that feeling in healthy people, using a so-called master-slave robotic system to throw off the individuals' brains. The "master" robot in front of the person would record his movements, while the "slave" robot behind the person would match them.
In one set of tests, when the person poked the robot in front, the robot behind would poke the person at exactly the same time. The test subjects reported feeling as if they were poking themselves. Blanke said it "creeped them out," but it didn't trigger a FoP.
But if the robot's poke in the back was slightly delayed, creating a a sensory-motor mismatch, some of the test subjects said it felt as if another human being was doing the poking. Indeed, some reported feeling the presence of several other people in the room. The feeling was so strong and disruptive that one subject asked to leave.
The neurological misfires triggered by the Swiss experiment don't rule out the existence of ghosts, of course. But they do suggest that some paranormal phenomena may come from the brain's own misdirection.
Tina Booth, a 29-year-old aquarium worker in Cincinnati, said she regularly has a FoP at home, and she attributes it to her grandparents, who have passed away.
"One time I got into bed, and one side of my cheek got super cold, then started to warm up -- and the weirdest thing was I wasn't scared," she told HuffPost Weird News. "I also can 'feel' someone in a room even though I'm the only one in it at the time."
Bryan Bonner, a skeptic about ghosts and an investigator with the Rocky Mountain Paranormal Research Society, said stories like Booth's are common. "Most people we deal with are reasonably healthy when it comes to psychology, but because of the human condition, we’re predisposed to see faces or hear recognizable sounds in white-noise situations," he said.
Bonner tries to find the source of such ghostly phenomena, whether it's a raccoon in the attic or something less explicable.
"There are a lot of factors that make this feeling happen, which is why [the Swiss experiment] is interesting," he said. "People often jump to conclusions about their own feelings as paranormal, but we have to stay open-minded: Could it be a ghost? Sure. Could it be a loose pipe or a brain misfire? Absolutely!" he added.
In sum, it might be your brain that's haunted, not your house.
Booth said her belief in her grandparents' presence isn't shaken by the study.
"That is a pretty neat experiment," she said. "I think the brain can cause these feelings, but I also think the supernatural can as well. ... I believe that everyone can feel energy. It's like when someone leaves a room because it feels tense. ... We can sense things even though we can't physically see them."