Have you read this already? How Déjà vu Works

By Sage Wesenberg, Biochemistry, 2019

“Woah, I just had déjà vu!” is about the only proof there is that a person has experienced the phenomenon commonly known as déjà vu, meaning “already seen” in French. Although it is so mysterious and difficult to pin down, about 60–70 percent of the population, mostly people ages 15 to 25, has claimed that they have felt déjà vu at least once in their life. However, many people think they are experiencing déjà vu when it is in fact something different.

Déjà vu is thought to last between 10 and 30 seconds, and is the feeling you get that you have experienced something extremely similar before. It is not a prediction that something is about to happen and will go a certain way, and then it does. While there may be a few different types of déjà vu, the most basic way to describe it is that you’re all of a sudden experiencing something that you’ve experienced before.

There are thought to be two main types of déjà vu. Associative déjà vu occurs in healthy people and is the most common. This is the type of déjà vu that was described above. Additionally, there are some brain conditions that may also cause some form of déjà vu. Biological déjà vu occurs in people with temporal lobe epilepsy. This is a type of epilepsy with recurring seizures stimulated from the middle and sides of the temporal lobes.

Often, right before a seizure, people with this condition may experience very strong déjà vu. This version may possibly be a little different however, because this déjà vu causes the person to feel as though they’ve already experienced the entire event occurring, not the very short bits that a healthy brain would experience in déjà vu.

Several different theories from different scientists come together to give us some information about déjà vu, but it is a sensation that proves very difficult to study. Researchers would like to use biological déjà vu to try and pinpoint a part of the brain where the déjà vu is occurring before a seizure, but right now, the cause is unknown. Obviously, this is because it happens randomly, with no warning, and with no real proof.

In the 20th century, the general explanation for déjà vu was paramnesia. Paramnesia causes memories to be inaccessible because they were from a stressful or difficult situation. Sigmund Freud developed this idea and said that the déjà vu moments came from these hidden memories.

Now that we know more about the brain, scientists have some different ideas. Because the temporal lobe of the brain is essential for our conscious memory, and the hippocampus helps us recall specific things and events, these parts of the brain are assumed to have something to do with the feeling of déjà vu.

Dr. Alan Brown of Duke University developed the Divided Attention, or cell phone theory, to recreate something similar to déjà vu. His study involved showing a series of photos to a group of students. Before seeing these photos however, some of the same photos were flashed on the screen for just 10 milliseconds. This is long enough for the brain to register the photo, but not long enough for the student to know they’ve seen it. Afterwards, the photos that had been flashed on the screen were thought to be familiar at very high rates.

He used this information to develop the cell phone theory which says that when we’re distracted, we subliminally take in our surroundings, but not enough to register it consciously. Then, if we go back through those same surroundings while focused, the area will for some reason seem familiar. Brown uses another example of this to explain some thoughts on déjà vu: You walk into your friend’s house for the very first time and you are deep in conversation when you walk in. During this conversation your brain is processing the room but the rest of you is distracted. Then, when you stop the conversation to actually look around, it feels like you’ve been there before, but really your brain is just a little bit ahead of you.

Another theory that can be applied to déjà vu is the hologram theory by Dutch psychiatrist Hermon Sno. He believes that memories are very similar to holograms. With just a piece, you can recreate in your mind the entire 3D image. But the smaller that piece gets, the fuzzier the whole picture is.

So perhaps this is what happens in déjà vu. Some very small detail in your surroundings, like a color or a sound, reminds you of something you remember from your past. And with that, you fill in the whole memory. Even though it’s not happening again, that small fragment and your brain filling in around it can make it really feel like déjà vu.

A lot of memories and moments of déjà vu can also come from other places, like movies, books, and dreams. Precognitive dreams may be the source of many déjà vu experiences, since often they are not remembered but can feel very real if you’re experiencing something similar.

Either way, déjà vu may be strange and disorienting, but….wait, I feel like I just read that…Déjà vu!