Déjà vu is French for ‘already seen’. It is a feeling that the situation(or surrounding) is familiar subjectively, but unfamiliar objectively.
Almost two-thirds of individuals have experienced Déjà vu at least once in their lifetime, including blind people.
Déjà vu is a fleeting, intangible experience, making it hard to measure, and is also highly subjective.

Déjà vu

Self Improvement

Déjà vu can be explained in terms of our memory:
<ul><li>Single Event Familiarity: When one element is familiar but other elements are not.</li></ul>Example: When you see a person you vaguely recognize(like your barber) out in the street. 
<ul><li>Gestalt Familiarity: When the layout and surroundings seem familiar.</li></ul>
Example: A layout of a room is similar to a room you have seen before but some details are not matching.

Our Memory

Déjà vu can be explained in terms of our neurological activity: 
<ul><li>Spontaneous Brain Activity: When a part of your brain is engaged with memory, thoughts can overlap, and one can experience a false sense of familiarity. The complex memory structures result in cross-connections.</li><li>Neural transmission speed: Déjà vu can be felt when the various parts of one’s brain that transmit information get disrupted, or if the information arrives at different times, like a traffic jam in the brain’s highways.</li></ul>

Our Neurology

Déjà vu is French for ‘already seen’. It is a feeling that the situation(or surrounding) is familiar subjectively, but unfamiliar objectively.
Almost two-thirds of individuals have experienced Déjà vu at least once in their lifetime, including blind people.
Déjà vu is a fleeting, intangible experience, making it hard to measure, and is also highly subjective.

That Familiar Feeling

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If you've ever had the feeling that a situation feels very familiar even though you know it shouldn't feel familiar at all, like if you're traveling in a city for the very first time, then you've probably experienced d&#233;j&#224; vu. D&#233;j&#224; vu, which means "already seen" in French, combines objective unfamiliarity - that you know, based on ample evidence, that something shouldn't be familiar - with subjective familiarity - that feeling that it's familiar anyway.
D&#233;j&#224; vu is common. According to a paper published in 2004, more than 50 surveys on d&#233;j&#224; vu suggested that about two-thirds of individuals have experienced it at least once in their lifetime, with many reporting multiple experiences. This reported number also appears to be growing as people become more aware of what d&#233;j&#224; vu is.
Most often, d&#233;j&#224; vu is described in terms of what you see, but it's not specific to vision and even people who were born blind can experience it.
D&#233;j&#224; vu is difficult to study in the laboratory because it is a fleeting experience, and also because there is no clearly identifiable trigger for it. Nevertheless, researchers have used several tools to study the phenomenon, based on the hypotheses they've put forward. Researchers may survey participants; study possibly related processes, especially those involved in memory; or design other experiments to probe d&#233;j&#224; vu.
Because d&#233;j&#224; vu is hard to measure, researchers have postulated many explanations for how it works. Below are several of the more prominent hypotheses.
Memory explanations of d&#233;j&#224; vu are based on the idea that you have previously experienced a situation, or something very much like it, but you don't consciously remember that you have. Instead, you remember it unconsciously, which is why it feels familiar even though you don't know why.
Single element familiarity The single element familiarity hypothesis suggests you experience d&#233;j&#224; vu if one element of the scene is familiar to you but you don't consciously recognize it because it's in a different setting, like if you see your barber out on the street.
Your brain still finds your barber familiar even if you don't recognize them, and generalizes that feeling of familiarity to the entire scene. Other researchers have extended this hypothesis to multiple elements as well.
The gestalt familiarity hypothesis focuses on how items are organized in a scene and how d&#233;j&#224; vu occurs when you experience something with a similar layout. For example, you may not have seen your friend's painting in their living room before, but maybe you've seen a room that's laid out like your friend's living room - a painting hanging over the sofa, across from a bookcase. Since you can't recall the other room, you experience d&#233;j&#224; vu.
One advantage to the gestalt similarity hypothesis is that it can be more directly tested. In <a href="https://www.ncbi.nlm.nih.gov/pubmed/22322010">one study</a>, participants looked at rooms in virtual reality, then were asked how familiar a new room was and whether they felt they were experiencing d&#233;j&#224; vu.
The researchers found that study participants who couldn't recall the old rooms tended to think a new room was familiar, and that they were experiencing d&#233;j&#224; vu, if the new room resembled old ones. Furthermore, the more similar the new room was to an old room, the higher these ratings were.
Neurological Explanations Spontaneous brain activity Some explanations posit that d&#233;j&#224; vu is experienced when there is spontaneous brain activity unrelated to what you're currently experiencing. When that happens in the part of your brain dealing with memory, you can have a false feeling of familiarity.
Some evidence comes from individuals with <a href="https://www.thoughtco.com/temporal-lobes-anatomy-373228">temporal lobe </a>epilepsy, when abnormal electrical activity occurs in the part of the brain dealing with memory. When the brains of these patients are electrically stimulated as part of a pre-surgery evaluation, they may experience d&#233;j&#224; vu.
One <a href="https://www.ncbi.nlm.nih.gov/pubmed/11884648">researcher</a> suggests that you experience d&#233;j&#224; vu when the <a href="https://www.thoughtco.com/hippocampus-anatomy-373221">parahippocampal system</a>, which helps identify something as familiar, randomly misfires and makes you think something is familiar when it shouldn't. 
<a href="https://www.clinph-journal.com/article/S1388-2457%2811%2900561-X/fulltext">Others have said</a> that d&#233;j&#224; vu can't be isolated to a single familiarity system, but rather involves multiple structures involved in memory and the connections between them.
Neural transmission speed Other hypotheses are based on how fast information travels through your brain. Different areas of your brain transmit information to "higher order" areas that combine the information together to help you make sense of the world. If this complex process is disrupted in any way - perhaps one part sends something more slowly or more quickly than it usually does - then your brain interprets your surroundings incorrectly.
An explanation for d&#233;j&#224; vu remains elusive, though the hypotheses above appear to have one common thread: a temporary error in cognitive processing. For now, scientists can continue to design experiments that more directly probe the nature of d&#233;j&#224; vu, to be more certain of the correct explanation.
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If you've ever had the feeling that a situation feels very familiar even though you know it shouldn't feel familiar at all, like if you're traveling in a city for the very first time, then you've probably experienced déjà vu.

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Bite‑sized knowledgeto upgradeyour career

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Our Neurology

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Bite‑sized knowledge
to upgrade
your career