About 1 in 5 Americans say they’ve seen a ghost. If you’re not one of them, your brain might be the reason.

According to Melissa Maffeo, a psychology professor at Wake Forest University and author of Science of the Supernatural, there’s no shortage of very un-spooky explanations for seemingly paranormal experiences. Writing for The Conversation, Maffeo argues that roughly three-quarters of Americans believe in some form of paranormal activity, and a specific combination of neurological and psychological factors can make certain people way more susceptible to those experiences than others.

The environment might be doing more than you think

Ghost hunting shows love a good EMF reading, and there’s actually a reason for that. Research conducted in Edinburgh’s South Street vaults and England’s Hampton Court Palace both found higher electromagnetic field variability in areas with reported paranormal activity. Whether that means ghosts cause EMF fluctuations, or EMF fluctuations cause the impression of ghosts, is an open question. In lab settings, manipulating EMF didn’t produce paranormal perceptions — but the people who did report strange sensations were the same ones who already believed.

Your brain can manufacture a haunting

A brain region called the temporoparietal junction helps you feel located inside your own body. Disrupt it — even artificially, through mild electrical stimulation — and people have reported sensing shadowy figures or floating outside themselves. Sleep paralysis is another culprit. When someone wakes mid-REM cycle, unable to move, still half-submerged in a dream, the brain scrambles to make sense of the sensory mismatch. Fear kicks in, and fear makes hallucinations feel very, very real.

Personality plays a bigger role than most people want to admit

People who score high in what psychologists call schizotypy — a cluster of traits including magical thinking, unconventional perception, and blurred self-other boundaries — are significantly more likely to believe in the paranormal and to experience spontaneous sensory phenomena. Schizotypy isn’t schizophrenia, but the traits do share neurological overlap, particularly around that same temporoparietal junction.

The bigger point Maffeo makes is that belief itself functions as a kind of glue. In one study, participants walked through a disused Illinois theater. Those who were told it was haunted reported strange sensations. Those who weren’t told anything reported nothing.

Your brain might already have a ghost waiting. It just needs the right invitation.