It’s an eerie feeling: You walk into a place you know you’ve never been before but are overwhelmed by a sense of familiarity—a memory you can’t quite reach. Has this all happened before?
Most people experience this sensation, known as déjà vu, at some point in their lives. It’s a hard feeling to study, though, because it tends to arise spontaneously and be shaken off easily, scientists say. Re-creating it on command in a laboratory is tricky business.
Nevertheless, scientists think that déjà vu actually provides a peek into how the memory system works when it goes a little off-kilter. The feeling may arise when parts of your brain that recognize familiar situations get activated inappropriately, says Akira Robert O’Connor, a cognitive psychologist at the University of St. Andrews in Scotland, who researches déjà vu. When this happens, another region of the brain then checks this feeling of familiarity against your recall of past experiences. When no actual matches are found, the result is a discomfiting sense of having seen it all before, accompanied by the knowledge that you haven’t.