When things go bump in the night, is it actually our brain that's bumping? Or is there something truly spooky behind some of those Halloween ghost stories?
In a recent poll, more than a third of those surveyed said they believed in ghosts - and almost a quarter said they had been in the presence of a ghost. Our unscientific Live Vote is even more gung-ho on ghosts.
Scientists have enlisted the tools of their trade - ranging from brain scanners and electrodes to virtual reality - to unravel the neurological roots of such phenomena. Some of the weird stuff we perceive is merely the result of our propensity for pattern recognition, they say. If we're in the right setting for a scare, it doesn't take much to set off our perception of the paranormal.
Other phenomena are weirder, but still of natural rather than supernatural origin. One research group used electrical stimulation to create that creepy feeling of being haunted. Other experimenters simulated an out-of-body experience. Still other scientists have linked near-death experiences and sleep disorders, or concluded that alien-abduction experiences are related to sleep paralysis.
Will all our spooky experiences be reduced to neural flashes inside our brains? Some of those who cover the paranormal beat say that's the way we're heading - but others say there are some things that just can't be explained away with a brain scan.
"The brain stuff is very, very limited," said British psychologist Richard Wiseman, who investigated (and ultimately debunked) the case of the Hampton Court haunting. "Basically you've got your head in a scanner. ... The interesting work is being done out there in the real world, as it were, rather than the artificial world of the brain scanner."
Deborah Blum, the author of "Ghost Hunters: William James and the Search for Scientific Proof of Life After Death," finds herself caught right in the middle. She points to the research into the simulation of a spooky "shadow person" as an example.
"It's a classic example of two ways of seeing the world," Blum told me. "If you're a neuroscientist and you look at that, you say, 'Duh, I've now solved the mystery of ghosts.' But if you're someone who believes in the supernatural, you say, 'Duh, everyone knows that spirits communicate through telepathic transmission. You're just duplicating what a ghost does.'"
The science of spooks is an exceedingly slippery thing, as scientists discovered more than a century ago. Blum documents how William James and other notables such as pioneer evolutionist Alfred Russel Wallace tried to find whatever scientific truth lay behind the spiritualism of those times.
Their efforts ultimately fizzled out, draining their credibility in the process - and Blum wonders whether the outcome proved that "science isn't a good match to study this stuff." Scientists can replicate electrical jolts and dopamine rushes - and if they're given enough time, they can suss out the hoaxes and the media-driven misperceptions that give rise to most paranormal reports. But some cases still remain resistant to the scientific method.
"You can't do it with these kind of phenomena, if they exist," Blum said. "Either they're not real, or you can't measure them."
Blum is particularly intrigued by a phenomenon known as crisis apparations - a sense that you're on the receiving end of a psychic communication from a loved one in peril.
"What I think is, there's no compelling case that we're communicating with the dead," she said. "There's a lot of interesting evidence, which we don't understand, that we communicate with each other on a subconscious level. So I think we're at this great point of being able to sort some of this out, but none of it so far says to me that we've solved all the mysteries of the universe."
Whether or not we finally solve those mysteries, ghostly tales have been part of the human psyche since - well, since the earliest records of the human psyche. And for Blum, that's one of the most interesting mysteries out there.
"Why have we seen ghosts since forever? The Egyptians reported seeing them. We report seeing them. Why?" she asked. "I do think that part of figuring out what we perceive as the supernatural is figuring out who we are."
In that spirit (heh, heh), feel free to chime in with your own Halloween ghost stories - or, for that matter, stories of how you debunked ghostly claims.