They’ve seen it all before—day after day, unceasingly, and to a degree that has become disabling: An 81-year old man no longer watches television or reads the papers because everything seems like old news to him. A 71-year-old woman stops listening to the radio, bored, because to her everything she hears sounds like a repeat broadcast. Indeed, after the deadly terrorist bombing in Bali on October 12, 2002, she felt as if she already knew the number of people hurt and killed before it was announced. Upon her first meeting with a staff member of a memory clinic, a 66-year-old woman feels as if she has met the man countless times already and kisses him politely on the cheek as if greeting an old friend. She is frequently depressed and confused, unable to shake the recurring feeling of déjà vu.

These patients, being studied by a group of memory researchers in England, suffer from a form of extreme déjà vu—the feeling of having experienced something before that you actually couldn’t have. But even when déjà vu strikes occasionally, it can be an unsettling experience. But after nearly two centuries of pondering the matter,  philosophers, psychologists, self-described experts on the paranormal, and, more recently, brain researchers all remain at a loss to offer a convincing and provable explanation for déjà vu.

Alan Brown, Ph.D., a research psychologist at Southern Methodist University (SMU) in Dallas, Texas, is among those who have not quite solved the mystery of what he calls the “déjà vu illusion.” However, unlike some of his colleagues, he’s not afraid to try. “Most scientists might not touch this because it’s too ambiguous or too strange,” Brown explains. “And they might worry about their reputation for tackling something that looks too close to voodoo, past life experiences, or demonic possession.” And no surprise: In past surveys by psychologists, Brown laments, déjà vu was mixed with questions about past life experiences, ESP, precognition, and alien abductions. “People keep lumping it in with something that’s paranormal or odd."

Brown and colleague Elizabeth Marsh, Ph.D., a psychologist at Duke University in Durham, North Carolina, have taken a preliminary step toward finally giving déjà vu serious scientific scrutiny. They hope it will finally coax explanations of déjà vu out of the realm of informed speculation. In pilot studies at Duke and SMU, they have induced a kind of false feeling of déjà vu in student volunteers. It may not be exactly like déjà vu, but Brown hopes it will be close enough to rally the interest of more scientists. “What I’d like to do is push people into this and take it in different directions,” Brown says. “Maybe loosen them up a little bit, make them bolder, more curious, a little more risk-taking."

Hiccups of Perception

Since the 19th century, many have plumbed the nature of déjà vu. In Victorian England, some people were convinced that déjà vu experiences were echoes of memory from past lives. Scholars and academics, too, were intrigued by the phenomenon. In his 2004 book, “The Déjà vu Experience: Essays in Cognitive Psychology,” Brown identified at least 30 plausible explanations for déjà vu. He believes that three categories or types of explanations are suitable for scientific testing: biological dysfunction, implicit familiarity, and divided perception.

The biological dysfunction model looks at déjà vu as a momentary glitch—a “hiccup,” as Brown puts it—in the brain’s processing of information. Our perceptions of the world—what we see, touch, smell, and feel—at some point are nerve impulses traveling from our sensory organs to the brain. The brain processes the information and ultimately produces a thought or impression.

Take the typical déjà vu experience: You walk into the kitchen of a friend’s new house. You know objectively that you have never been there, but it all seems familiar—the brightly colored Mexican tile floor, he arrangement of bric-a-brac on the counter, the smell of coffee brewing. “That’s weird,” you say, “I feel like I’ve been here before."

Or perhaps when you first walked into the room and absorbed its sensory gestalt, your brain did actually “see” it twice. Perceptions are conveyed via nerve impulses that travel multiple pathways through the brain to higher processing centers that integrate the disparate perceptions into a unified whole. If on the way some of the nerve impulses speed up or slow down, two identical versions may arrive at slightly different times, like the delay echo you sometimes hear during a phone conversation. The brain might misinterpret the echo as a separate event, giving you the impression that you’ve perceived the experience already.

The Cell Phone Syndrome

Purely psychological, as opposed to neurological, explanations of déjà vu have also been proposed. One, called divided attention, invokes the effect of momentary distraction to explain how it might seem that we have experienced something twice. Imagine you’re walking down the street in an unfamiliar city trying to find your friend’s apartment. You’re talking with her on your cell phone, getting directions. Your eyes are open, you’re dodging passerbys and other obstacles, but you are not concentrating entirely on your environment. You turn down a street that opens up to a new pedestrian shopping mall, just completed last week and opened to the public. You have never been here, because it didn’t exist until a week ago, and besides, you’ve never even been to this city. Yet it seems jarringly familiar. You have an overpowering feeling you have been to this spot before. What happened?

The divided perception theory of déjà vu says that as you turned down that street, you saw the scene of the pedestrian mall and your brain processed it in a shallow way, lacking the conscious awareness of, “Hey, that’s a pedestrian mall.” Remember, you’re devoting a pretty significant chunk of your awareness to the cell phone. A moment later, you devote your attention onto the scene fully and consciously perceive it. Your brain does a sort of perceptual double take, but the brief gap between your shallow and full awareness of the scene is mistaken for a longer period of time than, say, a momentary blink of time.

Familiarity Breeds Déjà Vu

The “implicit familiarity” hypothesis of déjà vu  says that if portions of a new experience match some aspects of something we have experienced in the past, then the mind may mistake that for a perfect match between the two experiences. The prior experience could have occurred in childhood, or even not at all in cases where you “remembered” it from a particularly vivid scene in a novel or film. For example, as a child you visited your grandmother every Sunday. She would always sit on her antique couch that smelled faintly of must and her lilac-scented perfume.

Fast-forward 40 years: you walk into a friend’s new apartment. You take 10 steps from the door, turn, and sit down on your friend’s antique couch. It just happens to be the same type of couch Grandma owned, complete with that same faint musty smell. The scent of lilacs in bloom outside the window wafts into the room. You are seized with a powerful feeling that you have already sat on this very couch in this very room in the same way. Or just the arrangement of items in the room could trigger the déjà vu, according to this hypothesis. The familiarity of the experience is implicit—felt and understood—but the person is not explicitly or consciously aware of the prior experience that caused the déjà vu.

And The Winner Is….

These explanations are based largely on speculation, not data. In part, scientific study of déjà vu is hampered by the fact that it is so ephemeral: It comes suddenly, initiated by no obvious or consistent trigger, and fades away quickly—usually in less than 30 seconds. It is also relatively rare: a typical person may have a déjà vu experience no more than once or twice per year, and many people not at all. In fact, information from surveys suggests that déjà vu experiences drop off gradually with age.

Brown and Marsh decided to put the implicit familiarity theory to the test. In the pilot studies at Duke and SMU, students were shown a variety of photographs from the two campuses. They were asked to find a small cross imprinted on each photograph. A week later, the students returned. They were shown the photos they had already seen, plus some new ones mixed in. Then they were asked to identify the places in the photos where they felt they had been before. Students who actually had been to any of the locations were identified and excluded; but even among the rest, some did say they felt as if they had visited some of the locations. The exposure to the photos a week earlier had been so superficial that the students had no explicit recollection of having seen the location in a photo, as opposed to actually having visited them. “What we’re doing is trying to induce that confusion by a very brief prior exposure, sort of planting a seed in the brain and the that thing sort of pops back up without any ability to say, hey, I saw that in the last session,” Brown says.

This study does not prove that all déjà vu experiences trace to a vague feeling of familiarity mistaken for explicit memory. The idea here was to induce, in a controlled setting, what psychologists call the familiarity response—a normal function of the mind that very likely has something to do with the déjà vu experience. “Every time we experience something, we have a familiarity or unfamiliarity response,” Brown explains. “And often it goes unnoticed. It’s like your heartbeat: you don’t notice it until it goes wrong and skips a beat……It’s almost biologically necessary to our survival. We have to know what’s familiar and what’s not to be safe. Even in what we eat, we shy away from unfamiliar things. There’s a strong tendency in most people toward neophobia, to be very wary of new things.”

Brown asked the students at the end of the study whether they had experienced anything like déjà vu. About half of them said they did. Even so, Brown freely admits that what the students in the study experienced was not really déjà vu. But it may have been similar enough to allow scientists to design more studies to probe the nature of déjà vu. They might, for example, scan brain activity as a person runs through the test, perhaps revealing which areas of the brain are active when somebody experience déjà vu. Or, the experimental technique would make it possible to narrow down the conditions that make it more likely for a person to experience déjà vu. “What we’re doing, as a first step, is just seeing if we can get people to mistakenly say they have physically been here or done that, but in fact they couldn’t have,” Brown explains. “It’s kind of a piece or fragment of the déjà vu experience.”

In another pilot study Brown and Marsh are working on, students are shown place images very briefly—on the order of 10 to 20 milliseconds. This is just long enough to engage the brain without sparking a conscious awareness of the scene. Immediately following this subliminal exposure, the image comes back on screen long enough to enter consciousness. The test subjects are asked if the scene looks familiar. This, says Brown, simulates the conditions under which people may experience déjà vu according to the cell-phone syndrome. “People are walking around or driving talking on a cell phone and they are not really taking things in. It’s hitting their eyeballs and activating some neurons, but they’re very unaware of it.” Again, it’s not exactly déjà vu in full, but the experiment takes the study of déjà vu another step closer to scientific scrutiny.

Where Is Déjà Vu In The Brain?

Some researchers have sought clues to the underlying neural circuitry of déjà vu—where, exactly, does it occur in the brain? The trail is leading to a specific fold of gray matter in the regions of the brain central to creating and processing memories: the parahippocampal gyrus. This lies within the temporal lobes, which are the portions of the brain that lie on the side of the head at roughly ear level.

The evidence is indirect but very suggestive. Some people with temporal lobe epilepsy—recurrent seizures originating in the temporal lobes—sometimes experience déjà vu. It’s part of the anticipatory mental state, or “aura,” that often precedes a seizure. Auras last a few seconds, often marked by sensations such as an odd smell, a tingling feeling, or a sensation of falling. This once led some scientists to conclude that déjà vu itself was a seizure—a view now discredited.

In another instance, researchers implanted electrodes in the parahippocampal gyrus to map the site of origin, or focus, of seizures in a person with temporal lobe epilepsy. Applying electric current to the electrodes triggered a feeling of déjà vu in the patient.

It makes sense that the parahippocampal gyrus might be involved in déjà vu experiences. “This is the area where we evaluate our memory experiences, where we evaluate context and familiarity,” Brown says. “People who have unusual cases of déjà vu almost always seem to have pathology in that particular area of the brain.”

Pathological Déjà Vu

Which brings us back to those four patients in England with persistent déjà vu—or, to be more precise, déjà vecu, which means “lived through this moment before.” In each case, the patients complained to their doctors of memory problems as well as persistent déjà vecu. Tests and diagnosis showed that each had some sort of brain abnormality, such as Alzheimer’s disease, a brain hemorrhage, or shrinkage in the temporal lobes or the brain as a whole. Martin Conway, Ph.D., a psychologist at the University of Leeds, explains that the common denominator is the circuit in the temporal lobes that trips when we have a “recollective experience.”

Recollective experience is the sense of the self in the past. It goes beyond a vague feeling of familiarity: A recollective experience is one in which you explicitly remember having lived through something before. A person with a normally functioning brain would likely react to an episode of déjà vecu with an objective realization that it cannot, in fact, be the case.

This “executive function” of the brain does not appear to operate in the patients Conway and his colleagues are studying. In these people, Conway says, the recollective experience circuit is stuck in the ON position. As a result, everything they experience in the present is perceived as a repeat of an identical past event. He argues that this same circuit is responsible for déjà vecu in people with healthy brains. It may just switch on by mistake because of some mundane trigger, like being tired or distracted. “It just happens much less frequently in the normal, undamaged brain,” Conway proposes.

Most intriguing, the four elderly people Conway and his colleagues have identified might be more representative than currently supposed. Degenerative processes that affect human memory with increasing age, Conway speculates, could make it more likely for people to experience persistent déjà vu or déjà vecu. Surveys suggest that déjà vu is actually less common in older people. But is this because older people are less likely to report strange mental states, perhaps fearing people might think they are getting a little batty? Conway thinks it’s worth exploring.

“We think the prevalence is actually a lot more than has been acknowledged before,” Conway says. “I think older people might go through quite intense and lengthy periods of déjà vu, but we just don’t know about it. A lot of older people feel reticent about strange experiences they’re having. If it really has not screwed up their lives, they tend to not mention it. You don’t go to your doctor and say doctor I keep experiencing déjà vu.”

Further Reading

• “The Deja Vu Experience: Essays in Cognitive Psychology,” by Alan S. Brown. (United Kingdom: Psychology Press (United Kingdom): May 1, 1994. 231 pages, hardcover.)
• “A review of the déjà vu experience,” by Alan S. Brown. (Psychological Bulletin, 2003, Vol. 129, No. 3, pp. 394-413.)
• “Persistent déjà vu: A disorder of memory,” by Rebecca G. Thompson and others. (International Journal of geriatric psychiatry, 2004, Vol. 19, pp. 906-907.