How Deja Vu Works

Have you ever visited a store for the first time and had it feel eerily familiar? Or maybe you’re deep in conversation with a friend and you suddenly get the feeling that you’ve had the exact conversation before, even though you know that you haven’t. If you’ve ever found yourself in either of these situations, you’ve experienced deja vu. Sixty to 70 percent of us admit to getting this feeling at least once in our lives. The sight, sound, taste or even smell of something makes us think that we’ve experienced it before, although we know that we couldn’t have.

There are more than 40 theories as to what deja vu is and what causes it, and they range from reincarnation to glitches in our memory processes. In this article, we’ll explore a few of those theories to shed some light on this little understood phenomenon.

What Deja Vu Is…And What It Isn’t

Chronic Deja Vu Recently, there have been studies of people who have what researchers are terming "chronic deja vu." Four senior citizens in the United Kingdom have experienced deja vu in a constant state. They refused to watch the news because they felt like they already knew what was going to be said (even though they really didn’t). Or, they wouldn’t go to the doctor because they felt like they had already been and didn’t see the point. Researchers have suggested that these individuals have experienced a failure in the temporal lobe. The circuits that are activated when you remember something have gotten stuck in the "on" position, so to speak. This has essentially created memories that don’t actually exist [ref].

Deja vu is a French term that literally means "already seen" and has several variations, including deja vecu, already experienced; deja senti, already thought; and deja visite, already visited. French scientist Emile Boirac, one of the first to study this strange phenomenon, gave the subject its name in 1876.

There are often references to deja vu that aren’t true deja vu. Researchers have their own definitions, but generally deja vu is described as the feeling that you’ve seen or experienced something before when you know you haven’t. The most common misuse of the term deja vu seems to be with precognitive experiences — experiences where someone gets a feeling that they know exactly what’s going to happen next, and it does. An important distinction is that deja vu is experienced during an event, not before. Precognitive experiences — if they are real — show things that will happen in the future, not things that you’ve already experienced. (However, one theory about deja vu deals with precognitive dreams that give us a "deja vu feeling" afterwards. See the Leading Theories section.)

Hallucinations that are brought on by illness or drugs sometimes bring a heightened awareness and are confused with deja vu. False memories that are brought on by schizophrenia can be confused with deja vu as well. Unlike true deja vu, which typically lasts from 10 to 30 seconds, these false memories or hallucinations can last much longer.

Defining types of deja vu is a very slippery area. Those who have studied it have applied their own categories and differentiations — each usually tied to a specific theory about what causes deja vu. Alan Brown, a professor of psychology at South Methodist University and author of "The Deja vu Experience: Essays in Cognitive Psychology," has three categories for deja vu. He believes there is deja vu caused by biological dysfunction (e.g., epilepsy), implicit familiarity and divided perception. In 1983, Dr. Vernon Neppe, Director of the Pacific Neuropsychiatric Institute in Seattle, proposed four subcategories of deja vu, including epileptic, subjective paranormal, schizophrenic and associative.

Taking a very broad look at the research and resources available, we can put deja vu experiences into two categories and then see the more subtle distinctions that researchers have placed on it:

• Associative deja vu
  The most common type of deja vu experienced by normal, healthy people is associative in nature. You see, hear, smell or otherwise experience something that stirs a feeling that you associate with something you’ve seen, heard, smelled or experienced before. Many researchers think that this type of déjà vu is a memory-based experience and assume that the memory centers of the brain are responsible for it.

• Biological deja vu
  There are also high occurrences of deja vu among people with temporal lobe epilepsy. Just before having a seizure they often experience a strong feeling of deja vu. This has given researchers a slightly more reliable way of studying deja vu, and they’ve been able to identify the areas of the brain where these types of deja vu signals originate. However, some researchers say that this type of deja vu is distinctly different from typical deja vu. The person experiencing it may truly believe they’ve been through the exact situation before, rather than getting a feeling that quickly passes.

Deja Vu Theories

Photo courtesy Dragan Sasic / Stock.xchng When we’re on a cell phone and driving, our attention is divided. Deja vu may work the same way.

Divided Attention (the Cell Phone Theory)
Dr. Alan Brown has attempted to recreate a process that he thinks is similar to deja vu. In studies at Duke University and SMU, he and colleague Elizabeth Marsh put the idea of subliminal suggestion to the test. They showed photographs of various locations to a group of students, with the plan to ask them which locations were familiar. Prior to showing them some of the photographs, however, they flashed the photos onto the screen at subliminal speeds — around 10 to 20 milliseconds — which is long enough for the brain to register the photo but not long enough for the student to be consciously aware of it. In these experiments, the images that had been shown subliminally were familiar at a much higher rate than those that were not — even though those students who had actually been to those locations had been pulled from the study. Larry Jacoby and Kevin Whitehouse of Washington University did similar studies using lists of words with similar results using lists of words.

Based on this idea, Alan Brown proposed what he calls the cell phone theory (or divided attention). This means that when we are distracted with something else, we subliminally take in what’s around us but may not truly register it consciously. Then, when we are able to focus on what we are doing, those surroundings appear to already be familiar to us even when they shouldn’t be.

With this in mind, it is reasonable to see how we might walk into a house for the first time, perhaps while talking to our host, and experience deja vu. It would work like this: before we’ve actually looked at the room, our brains have processed it visually and/or by smell or sound, so that when we actually look at it we get a feeling that we’ve been there before.

The Hologram Theory
Dutch psychiatrist Hermon Sno proposed the idea that memories are like holograms, meaning that you can recreate the entire three-dimensional image from any fragment of the whole. The smaller the fragment, however, the fuzzier the ultimate picture. Deja vu, he says, happens when some detail in the environment we are currently in (a sight, sound, smell, et cetera) is similar to some remnant of a memory of our past and our brain recreates an entire scene from that fragment.

Other researchers also agree that some small piece of familiarity may be the seed that creates the deja vu feeling. For example, you might go for a ride with a friend in an old 1964 Plymouth and have a strong deja vu experience without actually remembering (or even being aware of the fact) that your grandfather had the same type of car and you’re actually remembering riding in that car as a small child. Things like the smell and the look and feel of the seat or dashboard can bring back memories you didn’t even know you had.

Dual Processing (or Delayed Vision)
Another theory is based on the way our brain processes new information and how it stores long- and short-term memories. Robert Efron tested an idea at the Veterans Hospital in Boston in 1963 that stands as a valid theory today. He proposed that a delayed neurological response causes déjà vu. Because information enters the processing centers of the brain via more than one path, it is possible that occasionally that blending of information might not synchronize correctly.

Efron found that the temporal lobe of the brain’s left hemisphere is responsible for sorting incoming information. He also found that the temporal lobe receives this incoming information twice with a slight (milliseconds-long) delay between transmissions — once directly and once again after its detour through the right hemisphere of the brain. If that second transmission is delayed slightly longer, then the brain might put the wrong timestamp on that bit of information and register it as a previous memory because it had already been processed. That could explain the sudden sense of familiarity.

"Memories" From Other Sources
This theory proposes that we have many stored memories that come from many aspects of our lives, including not only our own experiences but also movies, pictures we’ve seen and books we’ve read. We can have very strong memories of things we’ve read about or seen without actually experiencing, and over time, these memories may be pushed back in our minds. When in we see or experience something that is very similar to one of those memories, we might experience a feeling of deja vu.

For example, as a child we may have seen a movie that had a scene in a famous restaurant or at a famous landmark. Then, as an adult, we visit the same location without remembering the movie, and the location appears to be very familiar to us.

Precognitive Dreams
Some researchers, including Swiss scientist Arthur Funkhouser, firmly believe that precognitive dreams are the source of many deja vu experiences. J.W. Dunne, an aeronautical engineer who designed planes in World War II, conducted studies in 1939 using students of Oxford University. His studies found 12.7 percent of his subjects’ dreams to have similarities with future events. Recent studies, including one by Nancy Sondow in 1988, have had similar results of 10 percent.

These researchers also tied evidence of precognitive dreams to deja vu experiences that occurred anywhere from one day to eight years later. The question has been raised about why the experiences themselves are typically mundane everyday things. One explanation from Funkhouser is that something more exciting is more likely to be remembered, making a deja vu experience less likely.

Although deja vu has been studied as a phenomenon for over a hundred years and researchers have advanced tens of theories about its cause, there is no simple explanation for what it means or why it happens. Perhaps as technology advances and we learn more about how the brain works, we will also learn more about why we experience this strange phenomenon.

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