You’re visiting a friend’s home for the very first time. But when you enter the living room, you are overcome with the sensation you’ve been here before. Indeed, you think you can even remember the distinct squeaking noise the leather sofa makes. But you know for a fact that you’ve never been here before in your life…
This is déjà vu, meaning “already seen” in French. About 70 percent of people claim to have experienced it at one time or another. It’s the vague and unsettling notion you’ve been somewhere or sensed or done something before.
For most of us, the reasons we experience déjà vu are almost as mystifying as the feeling itself. For scientists, it is a notoriously tricky phenomenon to collect data about. After all, the sensation lasts just a few moments at most, is impossible to predict and doesn’t happen very often.
Furthermore, there are various types of déjà vu, which further complicates the task of studying it. Déjà senti, for example, means “already thought.” Meanwhile, déjà visité refers to the feeling of having previously visited a place.
However, there have been a number of theories over the years that try to explain the phenomenon. French parapsychologist Emile Boirac was the first to coin the term “déjà vu” in his book The Psychology of the Future, published in 1918. He didn’t delve into why it occurs, though.
The father of psychoanalysis, Sigmund Freud, had a theory, of course. He suspected déjà vu offered glimpses of painful memories that people had locked away. This theory, dubbed paramnesia, then became the dominant explanation for déjà vu until recently.
Lately, a clutch of studies have come emerged that seem to provide more empirically supported insights into déjà vu. These studies look into cases of chronic déjà vu: cases involving people who are certain that almost everything they do or sense is not new to them. In fact, this condition can be debilitating.
Take, for example, this anecdote from Dr. Chris Moulin, a professor who studies memory at the Pierre Mendès-France University in Grenoble. “We had a peculiar referral from a man who said there was no point visiting the clinic because he’d already been there,” he told the University of Leeds, England, newsletter The Reporter in 2006.
Further study of the man revealed he was convinced there was not much he felt he not experienced before, even when watching the news on TV. When challenged on his assertion, he either demurred, claiming to have a condition, or argued convincingly that he had seen them.
Being able to study his condition offered potential new insights into déjà vu. But besides looking at people who suffered from the chronic disorder, Moulin and a team of scientists researched ordinary people too. They wanted to figure out how exactly the sensation is triggered in people who didn’t have the disorder.
To do this, Akira O’Connor, a Ph.D. student at the University of Leeds working with Moulin in 2006, took a number of students from the university for his study. First, he asked them to remember words, before hypnotizing them and inducing them to forget. Finally, he showed them the words. The students reported a sense of déjà vu and were then asked to write about their experiences.
While Moulin is most concerned with treating people who have chronic déjà vu, the study revealed more about its nature in ordinary people. It suggested that the conventional wisdom – which has it that déjà vu is a momentary lapse, or a hiccup in brain functions – might not be true. In fact, déjà vu might actually be the brain working hard at investigating memories to see whether they’re true or false.
In another experiment, conducted in 2016, O’Connor and a team at the University of St Andrews in Scotland scanned 21 volunteers using an fMRI machine. They wanted to see what happened in the brain when a person experiences déjà vu.
The team expected the hippocampus region of the brain to light up, since it is devoted to memory. However, what they saw was activity in the front areas of the brain, where decision-making takes place.
“It suggests there may be some conflict resolution going on in the brain during déjà vu,” Stefan Köhler, professor of Behavioral and Cognitive Neuroscience at University of Western Ontario, told New Scientist in 2016. Scientist think déjà vu is the brain going over old memories and checking them for mistakes – just in case.
This seems to make sense, given the other things we know about déjà vu. For instance, we know that it occurs more often among young people, who tend to have healthier and more active brains. As a result, not experiencing déjà vu may not be a good sign. “Without being unkind, [people who don’t experience déjà vu] don’t reflect on their memory systems,” Moulin said.
Of course, there is the possibility never experiencing déjà vu suggests having no memory mistakes. “It could be that déjà vu experiences make people cautious, because they might not trust their memory as much,” Köhler explained.
There are a number of other theories which attempt to explain why we experience déjà vu, however. For instance, a psychologist from Southern Methodist University in Texas, Alan Brown, believes déjà vu is the result of half-remembered events and places. He calls this his “divided attention” theory.
Take, for example, entering a room for the first time. It might have been that as you entered the room you were looking at your phone but subconsciously took in your surroundings. If Brown’s theory is correct, the feeling of déjà vu is your brain connecting your subconscious memory with your current experience.
So it seems as though déjà vu could be the brain checking that all the piping is working correctly, so to speak. Or it could be the brain’s way of telling us that we have two very similar memories, before trying to figure out just how similar they are. Regardless, it’s unlikely that knowing all this will make the sensation feel any less weird should you have it again…