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Trying to Explain the Unexplainable: “Déjà vu”‘s Mystery

In the 21st century, it feels like there are few things left that we don’t know. Thanks to modern-day medicine and centuries of reluctant researchers, we know bacteria is responsible for the flu, depression is due to chemical imbalances, and cigarettes kill. Compared to even the last century, our technology and knowledge is a thousand times more advanced.

What boggles my mind is that even some of the most simple-sounding human actions are left unexplained by scientists. Why do we yawn? What is the purpose of dreaming? And most interestingly – what is deja vu?

Feel like you’ve heard that question before? Deja vu, derived from the French term “already seen”, is an unexplained feeling that you are experiencing an action or moment in time over again. It’s very common, research shows that up to , and yet scientists are still stumped as to why it exists. Often times it’s a difficult situation to interpret.

The Trials and the Triumphs

Are episodes of déjà vu relapses of memories from a past life? Are they precognitive dreams, or dreams you previously had that told you the future? How about a side effect from alien abduction?

Tons of explanations exist in popular culture to try and interpret the phenomenon, because – well, it’s just plain interesting. The feeling of reliving a moment in time seems futuristic and science-fiction in itself, not to mention the actual scientific evidence behind it, which is extremely limited. Millions of people experience this mental illusion, on a weekly to monthly basis, with no obvious cause or side effects. That’s a lot of alien abductions.

Realistically, scientists have had a hard time determining the cause of déjà vu because it is based largely on self-reporting and difficult to compare intensities of episodes. The randomness of déjà vu also makes it nearly impossible to simulate in a lab experiment. It’s hard to record which areas of the brain are effected during an episode unless the test subject is hooked up to monitors 24/7, which surprisingly has a very slim number of volunteers.

Many scientists over the course of déjà vu study determined that it is active in the temporal lobes, specifically the medial lobes. The medial temporal lobes, toward the bottom of the human brain, are the center of long term memory storage. Within these lobes are the hippocampus, responsible for recollection of events, and the rhinal cortex, in charge of recognition of events. One explanation stems from these lobes and claims that during an episode of déjà vu, the rhinal cortex is activated while the hippocampus remains inactive. This explains why we recognize a memory as being familiar, but can’t recall any details, such as when the event happened previously. Another theory is that there is simply an error in the brain’s memory circuitry, and memories meant for short-term storage are graduated to long-term immediately. In this interpretation, it seems clear why a moment may have extreme familiarity,  but not trigger a full memory.

One study by Akira O’Connor at the University of St Andrews UK claims that déjà vu is the memory circuit of the brain checking itself. He did so by simulating the sensation of déjà vu in a lab study by triggering false memories. Volunteers were given a list of words all having to do with sleep, such as bed, dreams, etc., but not the word sleep itself. They were then immediately asked if any of the words they had been exposed to started with the letter s, which they answered no. Later, they were asked if they had heard the word sleep. Consciously they knew they couldn’t have, but the word seemed familiar. This false familiarity mimicked the familiarity of déjà vu enough to record which areas of the brain were stimulated.


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O’Connor’s team used an fMRI to show that the frontal lobes, involved in decision making, were activated during this study. His team concluded that déjà vu is most likely the result of our memory system checking itself and looking for memory errors. They didn’t however, find whether it is beneficial, or why some people experience it while others don’t, leaving the phenomenon a long-lasting mystery.

 How Déjà Vu Can Take Over Your Life

Déjà vu is just one aspect of a whole series of familiarity mental illusion, one of the most extreme being déjà vecu. While traditional déjà vu is random and fleeting, déjà vecu is more long-term, and a series of events can feel like they have already occurred instead of an individual moment. In these cases it can be extremely difficult for individuals to distinguish what is real and what isn’t. Pat Long from Mosaic Science recently explained that déjà vu had become a reality to him in the form of déjà vecu, and the results were much more than 10-30 seconds of harmless familiarity.

“The shock of repeated déjà vu isn’t physical, necessarily, but instead causes a kind of psychic pain that can feel physically sickening. Dream images suddenly interrupt normal thoughts. Conversations seem to have already taken place. Even banal things like making a cup of tea or reading a particular newspaper headline seem familiar. It feels occasionally like I’m flicking through a photo album containing nothing but the same picture reproduced endlessly.” – Pat Long

Researchers have claimed a connection between déjà vu occurrences and epilepsy by studying the over-activation of similar areas in the brain. Long, who had recently had surgery to remove a lemon-sized tumor from his brain, began seeing a connection between the frequency of déjà vu and his sudden seizures. He would experience an aura, or an onset, of déjà vu immediately before seizing, as well as continuously throughout the day. When it feels like you’ve already lived hours of your life before, distinguishing reality from just a malfunction of circuitry is almost impossible.

There seems, at first, to be so much about the world we already know compared to past generations. Realistically, there is so much still to learn through psychology, biology, physiology and everything in between – what is the most harmless cure to cancer? How can we prolong human existence? Do aliens even exist? Among these great mysteries lie the secret to déjà vu, but it’s only a matter of time.

Hamzelou, Jessica. “Mystery of Déjà Vu Explained – It’s How We Check Our Memories.” New Scientist, New Scientist, 16 Aug. 2016, www.newscientist.com/article/2101089-mystery-of-deja-vu-explained-its-how-we-check-our-memories/
Long, Pat. “Déjà Vécu: When Déjà Vu Becomes Your Reality.” CNN, Cable News Network, 1 June 2017, www.cnn.com/2017/06/01/health/deja-vu-vecu-mosaic-partner/index.html.

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Mallory Lamparter, B.S. Psychology
Mallory Lamparter, B.S. Psychology

Mallory Lamparter is pursuing a B.S. in psychology as well as a minor in public health. She hopes to specialize in sports psychology in graduate school. When she's not trying to figure out how our minds work, she's either playing volleyball for the University of Arizona club team or hiking with her puppy.

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