Imagine that you go to a friend's house for the first time and, upon entering, you feel that you have already been there, that you know the place even as if you knew where everything is. However, you know perfectly well that you have never been before.
That strange, fleeting sensation is what we call déjà vu, which means “already seen” in French. It's like your mind is playing a little trick on you, making you feel like you're reliving a moment that's actually completely new to you.
A very normal experience
Don't worry: feeling déjà vu is common. It has happened to most of us, and surely on more than one occasion. For this reason, this phenomenon – which in Spanish is also called paramnesia – is being widely researched and debated in such serious scientific fields as neuroscience and psychology.
In a study of 386 people, 294 (76%) said they had ever felt like “I've been through this before,” even though it didn't really happen.
But the older we are, the less it happens to us: of young people between 18 and 29 years old, almost 9 out of 10 have felt déjà vu. In people between 30 and 39 years old, it decreases a little, because 8 out of 10 have experienced it. And so it continues to decline: of those between 40 and 49 years old, around 7 out of 10 say they have felt it, among those between 50 and 59 years old, 6 out of 10, and between 60 and 69, the statistic already drops to 50 %.
There is more than one type of déjà vu
Three different types of déjà vu have been described: déjà visité, or “already visited”; déjà vécu, or “already lived,” and déjà senti, or “already felt.” Let's explain them with some example.
Déjà visitedé, what has already been visited, corresponds to the example with which we began this article: when you feel that you already know the place even though it is the first time you visit it.
Déjà vécu, what we have already experienced, occurs to us when we perceive that we have not only seen something before, but that we have lived it. For example, you are telling a story about your vacation and suddenly you feel that you have already told that same story, with the same details and with the same reactions from your friends, although you are clear that it is the first time you are doing it.
And an example of déjà senti, what has already been felt, can be when you hear someone say something for the first time and you have the feeling that they had already told you before. What a mess. In other words, as if in a dream someone had told you exactly the same thing, and it leaves you thinking “where have I heard that before?”
To make matters worse, the opposite of déjà vu can also happen to us: a jamais vu, or “never seen.” It occurs when something that is very familiar suddenly feels strange or new. For example, you are typing the word “phone” and suddenly it seems strange. You even wonder if it is well written, even though you know perfectly well what it is and you have written it thousands of times before. Hasn't it happened to you? Me.
But why does it happen to us?
Imagine that your brain is like a supercomputer that processes all the information you receive. Sometimes, this very powerful computer does things that are a little strange, and that is what gives us the strange feeling of “I have already experienced this.” Among the more than 800 scientific publications that, today, are found in the prestigious scientific database PubMed, we can detect various theories that try to explain this phenomenon.
One of them is the theory of neuronal desynchronization. To understand it, we must take into account how memory works, the brain system for storing messages in our brain. Usually, these messages pass through a control station (short-term memory area) before reaching their final destination (long-term memory area).
But sometimes a message takes a shortcut and goes straight to the end (to the long-term memory area), bypassing the control station. This confuses your brain, making you think that the message (the experience) is not new, but something you have received before. Synchronization between the groups of neurons in both areas has failed.
Another theory is that of fragmented memory. Now think about your memory being stored like a puzzle, and each thing we remember is a piece. Sometimes something happens in the present that perfectly fits a piece of the puzzle of your past memories, but you can't see the whole picture to know where it came from. This can make something completely new seem familiar, as if you've already experienced it.
There is also the theory of recognition errors. Your brain can simply get confused and think it recognizes something new as if you've seen it before, even when you haven't.
According to parallel processing theory, when the brain works on two tasks at the same time, it usually does so perfectly. But if for some reason the processing of one of those tasks is delayed, when the information finally arrives, the brain thinks that it had already processed it before. That's what gives us the feeling of déjà vu.
This theory is very similar to that of divided attention. Suppose you are listening to music while studying and you are not fully concentrating on either the music or the study. Later you might not remember well the task on which you were not focused. If, for whatever reason, something similar happens to us some time later, your brain will try to fill in the gaps with what it remembers, and that can make you feel as if you have already experienced that situation.
And finally, the theory of neural connections tells us that connections between different regions of the brain (so-called brain networks) can strengthen or weaken over time. Sometimes this causes a network to be activated that does not correspond to the situation that is happening. For example, a memory network that generates that feeling of familiarity is turned on in an unusual way.
Although these are some ideas to explain why déjà vu occurs, it still poses a big mystery to science. It's one of those weird and fascinating things that happens in our brains. (National Geographic) (Photo: iStock/ Taken from the Internet)
