The term déjà vu was coined by the French philosopher and parapsychologist Émile Boirac in 1876 and translates, literally, as ‘already seen’.
It’s that eerie, uncanny feeling you get when you sense that a supposedly new experience that you’re having right now is actually one you’ve had before.
You might be in a particular place – a café, say, or a street – and it feels familiar, even though you know you’ve never been there. It can be tempting to attribute the experience of déjà vu to the existence of ‘past lives’ or to some kind of a ‘glitch in the matrix’.
There’s a more down-to-earth explanation for what’s happening during these moments, though. And the good news for anyone who experiences déjà vu (which is about two-thirds of us), is that most of the time it’s actually a sign of healthy brain function.
According to the latest neuropsychological accounts, déjà vu occurs when certain aspects of a situation trigger a sense of familiarity, which is registered in a part of the temporal lobe called the perirhinal cortex. This could be caused by similarities to situations you’ve been in before.
Next, the hippocampus, another key memory structure also housed in the temporal lobe, fails to identify relevant memories to account for the feelings of familiarity.
Finally, this mismatch gets picked up by brain areas in the frontal cortex, such as the anterior cingulate cortex and medial prefrontal cortex.
This final stage gives rise to the uncanny feeling of having the sensation that you’ve been in this situation before, despite knowing that you haven’t.
Psychologists call this final stage ‘metacognitive awareness’ and it’s a sign of your brain working effectively to flag up the glitch.
In fact, when researchers have simulated déjà vu in a brain-imaging lab using memory games, it’s these frontal brain areas involved in meta-cognitive awareness that show greater activation, confirming the idea that the subjective sense of déjà vu is associated with the monitoring processes.
It’s true that excessive and unusual forms of déjà vu can manifest in some cases of pathology. For instance, people with temporal lobe epilepsy sometimes describe experiencing a form of prolonged déjà vu before a seizure.
Also, some people with dementia can experience what’s known as déjà vécu (meaning ‘already lived’), a kind of intense déjà vu in which the person really believes they’ve experienced a new situation already and acts accordingly, for instance, turning off the TV news because they think they’ve seen it all before.
If you’re experiencing the more typical, fleeting kind of déjà vu, you really have nothing to worry about. In fact, healthy déjà vu is more common in younger people and actually tends to become less frequent with age.
Psychologists think this is because the error-monitoring processes in the frontal cortex become less efficient as we get older.
So, the next time you have that eerie feeling, you can take comfort – there’s no glitch in the matrix and your brain is simply functioning as it should.
This article is an answer to the question (asked by Dom Anderson, Bournemouth) 'Is having déjà vu unhealthy?'
To submit your questions, email us at questions@sciencefocus.com, or message our Facebook, X, or Instagram pages (don't forget to include your name and location).
Check out our ultimate fun facts page for more mind-blowing science
Read more:
