There’s a 23­year­old British man who is trapped in time. Whenever he does something – anything at all – he gets an overwhelming feeling of déjà vu. And then he gets déjà vu of the déjà vu. Over and over and over again. He’s entered a never­ending abyss of time. He’s stopped reading newspapers, watching television or listening to the radio because he felt as though he had encountered it all before. He’s healthy, young and aware – but his history with depression and anxiety suggest that mental illness could be a potential cause of his chronic déjà vu.

This man’s case is an extraordinary one but more than two thirds of us experience an episode of déjà vu at least once in our lifetime. You may be having a conversation with a friend when suddenly that jarring, fleeting feeling that this has all happened before hits you. But you know that it hasn’t, that this is just another strange case of déjà vu. But despite it being such a common experience, it’s a poorly understood one.

Many theories exist, spanning from the paranormal (past lives and precognitive dreams) to memory errors and wish fulfillment (an unconscious recognition of dreams). Dr Akira O’Connor, a psychologist from the University of St. Andrews, believes that déjà vu is caused by a momentary misfiring of neurons in the brain. O’Connor states that this is supported by the association of déjà vu with temporal lobe epilepsy. Some epileptic patients consistently experience déjà vu before seizures or between convulsions. Epileptic seizures are caused by alterations in the electrical activity of the brain and déjà vu may be caused by a similarly dysfunctional electrical discharge.

But this pathological déjà vu could be very different to the typical déjà vu experienced by healthy individuals. Some researchers, such as Professor Anne Cleary from Colorado State University, speculate that déjà vu in otherwise healthy individuals is a result of a memory error. Cognitive psychologist Bennett Schwartz spoke of how he experienced déjà vu while touring a castle in Scotland. At the end of the tour he saw photographs of the castle taken from a movie which he had seen five years earlier. Until he saw them in the gift shop, he was unable to place the sense of familiarity he had experienced.

Schwartz’s experience of déjà vu is not uncommon – and fits with Professor Anne Cleary’s theory that déjà vu is the result of seeing something genuinely familiar in a novel situation, even if we aren’t able to place it. In order to test this theory, Professor Cleary and her colleagues created a virtual reality program, ‘Déjà Ville’ to consistently elicit déjà vu. ‘Déjà Ville’ incorporated 128 scenes divided into pairs that, unbeknownst to the participants, had objects (such as chairs and tables) in the same position on a grid to create identical layouts in space, in an attempt to elicit that uncomfortable familiarity that characterizes déjà vu.

As expected, participants most frequently experienced déjà vu when they encountered new scenes, which were spatially similar to previously encountered scenes but when they could not consciously recognise the resemblance. Professor Cleary’s findings from ‘Déjà Ville’ show that déjà vu commonly occurs when people have knowledge from their memories, without being able to retrieve the memory responsible.

We have a pretty good memory for objects – we can easily recognise a familiar object in an unfamiliar setting, for example if your friend has the same set of china that your parents have. But we’re not so good at retrieving memories based on the configuration or placement of objects. If you’re in a new place, in which unfamiliar objects are set up in a similar layout to something you have experienced before, you’re likely to get a feeling of familiarity without knowledge of the memory source.

As Cleary says: “One reason for the jarring sense that accompanies déjà vu may be the contrast between the sense of newness and the simultaneous sense of oldness – something unfamiliar should not also feel familiar.” It makes sense. A feeling of familiarity when encountering new places can indicate how you

It makes sense. A feeling of familiarity when encountering new places can indicate how you should act and what you should do next. Déjà vu is an incredibly unpredictable and personal experience, so it is nearly impossible to study in controlled conditions. There is no simple explanation as to how or why déjà vu occurs and more than one of the dozens of theories that do exist could be right. But perhaps part of the strange allure that déjà vu has is that it is inexplicable – a kind of remembering where we feel as though we’ve returned to a place we’ve never been.

But perhaps part of the strange allure that déjà vu has is that it is inexplicable – a kind of remembering where we feel as though we’ve returned to a place we’ve never been.