But we know less about why we have the feeling. Is déjà vu evidence of a past life, an out of body experience or just a good old neural misfire?
Most researchers who study this area of the brain vote for the last option, and they are busy trying to find all the reasons why.
of us experience déjà vu at least once in our lives, experts say. While there's no gender difference when it comes to the phenomenon, age does seem to matter. Déjà vu episodes drop dramatically in older adults; in fact, most reports come from people between age 15 and 25, leading some to wonder if déjà vu is connected to brain development. We now know the brain isn't fully formed until at least age 25, maybe even later.
Déjà vu is also most common in people with higher education
and socioeconomic class, and those who watch more movies and travel often
. If déjà vu is all about familiarity-based recognition, there's some logic to these statistics: Travel is most common among those with higher incomes, and traveling provides more opportunities to see new physical locations that might trigger a sense of familiarity, especially if those locations may have appeared in a previously viewed movie scene.
"Memory is far from perfect. We simply fail to recall everything that we encounter in day-to-day life," explained déjà vu researcher Anne Cleary
. "However, just because something fails to be recalled doesn't mean that the memory isn't still 'in there' somewhere; often it is, and it is just failing to be accessed. These types of memories might be what drive the sense of familiarity that presumably underlies déjà vu."
Research also shows déjà vu is more likely to happen if a person is under pressure or fatigued. Perhaps when we're tired, stressed or distracted we only recall a fraction of an event, just enough to trigger a sense of familiarity.
A 2010 study
found those of us who frequently remember our dreams seem to have more déjà vu experiences. Dreams are notorious for being less than faithful to reality. Add that to the already fallible memory system of our brains, and you can see why the two might interact to create a feeling of familiarity; maybe you dreamed it, or something like it.
There's actually a term for dream déjà vu: déjà reve, French for "dreamed before." About 86% of college students surveyed as part of a study report reliving events they remember from dreams. Cleary said she believes this might happen when you dream about something you've experienced, but later only remember the dream, not the event itself.
The brain on déjà vu
Since having a déjà vu experience is unpredictable, it has been tough to study. That's why some researchers are focused on the brains of patients with a certain form of epilepsy: specifically, those who often experience déjà vu during the "auras" that occur right before a seizure.
"The epilepsy patients whose seizures tend to trigger déjà vu have generally been patients whose seizures originate in the medial temporal region of the brain," said Cleary. "This same area of the brain is involved in memory."
In the medial temporal lobe of the brain sits the rhinal cortex, which helps us recognize that something is familiar. Close by is the hippocampus, responsible for new memory storage. Not far away is the amygdala, in charge of our emotions, which can drive memory storage and retrieval.
By sending an electric current into the medial temporal region of the brain, researchers have been able to trigger déjà vu experiences in epileptic patients and map brain activity. They found that even though the hippocampus is responsible for memory, it's easier to induce déjà vu via the rhinal cortex, the portion of the brain responsible for feelings of familiarity. Yet all three brain structures appear to be active during the episode.
Patients in these studies report two types of seizure experiences: One involves a feeling of déjà vu familiarity, the other a more vivid and complete recollection of an event from the past. That's known as déjà vécu', or "already lived." It has been suggested the two may fall on a continuum
, with déjà vu being a sort of low-level form of failed recollection.
Harnessing déjà vu into precognition?
Cleary, a cognitive psychologist Colorado State University, is using today's technology to recreate the experience of déjà vu. She has created a 3-D virtual village she calls "Deja Ville," based on the popular Sims 2 game, and is using it to explore the concept of Gestalt familiarity, the arrangement of objects within a scene.
"For every original scene created, we created another, different scene that mapped onto that original scene in its spatial configuration -- the configuration of elements on the grid," said Cleary. "For example, if the original scene was a courtyard with a potted tree in the middle, surrounded by flower beds and hanging pots on the courtyard walls, the corresponding similar scene might be a museum with a statue in the middle where the potted tree had been, surrounded by rugs in the same configuration as the flower beds, and candelabra in the same configuration as the hanging pots."
She also presented the subjects completely novel scenes, which didn't have any similar elements that might be "mapped" and recognized. She found there was a greater likelihood of reported déjà vu experiences when subjects failed to recall one of the previously seen mapped scenes.
She's now using the 3-D model to see if the memories that underlie a déjà vu experience can help us predict what happens next, serving as a form of "precognition."
"It's conceivable that a previous experience that exists in memory but that fails to be retrieved might not only produce a sensation of déjà vu upon encountering a highly similar situation, but also produce a sense of how the current event is supposed to unfold," explained Cleary, "such as which direction to turn next within the scene."
Could those insights give déjà vu a reason for its existence?
"Even when we fail to retrieve a memory," said Cleary, "our brains might have a way of signaling to us that there is possibly a relevant memory in there somewhere. That signal might be useful in that it can prompt us to keep searching our memory for whatever it is that is in there that might be relevant to the current situation."