knock, knock. Who’s there? Deja. Deja who? knock knock!

Hi everyone!

If it’s not clear from the ‘hilarious’ title I came up with (before having my morning tea lol) what I want to talk about in today’s post…it’s not you, it’s me lol! But anyway, I’m talking about Déjà vu– a french phrase meaning ‘already seen’! And why am I suddenly interested in this phenomenon you might ask, well that’s because I’ve been experiencing this bizarre feeling of ‘wait, didn’t this already happen before?’ more frequently than before! And so, I was curious what it meant ~~( am I more stressed and overworked than I realized?~~ ~~is my brain broken?~~) and did a completely unnecessary dive on the internet to learn more about this phenomenon. A part of what fueled this reading marathon (if you’d even call it that) was that I wanted to take a small break from reading scientific literature from my own discipline and figured, this would be a perfect chance to do so haha! 😀

So as you’d notice, this blog is pretty much an information/thoughts dump after I spent an afternoon learning more about this ‘spooky’ sensation. To put it simply, it is when you feel like you’ve done something or experienced something before. While my main goal was to learn what science thinks about Déjà vu, I did find a few articles and online chatting threads where people seemed to interpret it in more of a paranormal context, which I thought was interesting haha! Here’s a thread from Witchipedia for example.

Anyways, going back to the science side of this- most of the mainstream scientific research denies the paranormal (precognitive or prophetic) explanation for déjà vu, no surprises there! While, the exact reasoning behind the feeling of déjà vu is still not entirely understood (reasoning aside, it took scientists almost a century to finally settle on a term for this phenomenon lol), most of the competing theories so far support the idea of it being a memory anomaly. In other words, it’s when we encounter a situation that seems similar to an actual memory but we can’t fully recall that memory. In the end, we’re left with this feeling of familiarity that we can’t quite place. I like this explanation given by Akira O’Connor, a senior lecturer in the School of Psychology and Neuroscience at St Andrews University.

Déjà vu is basically a conflict between the sensation of familiarity and the awareness that the familiarity is incorrect. And it’s the awareness that you’re being tricked that makes déjà vu so unique compared to other memory events.

Further reading revealed that there are two main recognized types of déjà vu. The first type is pathological déjà vu, that’s often associated with temporal lobe epilepsy. In this case, research indicates that it’s a neurological anomaly related to the electrical discharge occurring during the epilepsy episode. Interestingly, scientists didn’t find any solid link between déjà vu and other mental disorders like anxiety, schizophrenia, and dissociative identity disorder. The second type is the non-pathological type, often experienced by about two-thirds of the ‘healthy’ population. In such cases, studies like this and this suggest that those who travel frequently or often watch movies/Tv-series are more likely to experience déjà vu than others.

I also wanted to see if other than neurological factors, things like a person’s age or gender are relevant to how they experience this sensation. And lucky for me, this paper by Alan Brown (2003) covers those points quite nicely. Turns out there are many studies that find that the feeling of déjà vu decreases with age. However, teenagers seem to be an exception to this trend! The following image from Brown (2003) shows results from various past studies that show lower rates for teenagers experiencing déjà vu.

This made me wonder if there’s a connection between how much your brain has developed and whether you experience déjà vu! The answer I got was- many scientists have suggested that the cognitive maturation necessary for déjà vu is not fully in place until the age of 8 or 9 years old. Also, one may notice that they’re experiencing a déjà vu only after learning or reading about it. And it’s safe to assume that this may not happen until the mid-teen years (Brown, 2003). So, in a way, this also means that the process of sample collection itself may dramatically change the outcome (especially for younger subjects). In terms of gender as an affecting factor, the results are pretty inconsistent. Some have found a higher incidence among women and others among men.

What exactly happens in the brain during déjà vu?

My initial goal going into this small reading adventure was to learn whether having frequent déjà vu experiences was a bad thing? Something like a sign of an unhealthy brain!? Turns out my worries are all for naught lol! While there isn’t a mutually agreed upon, universal model that explains exactly what happens in the brain during déjà vu, most of the theories share the same common idea. The temporal lobe of our brain sends the frontal regions of the brain signals that a past experience is repeating itself. The decision-making areas of the (frontal) brain then effectively check whether the signal is consistent with what is possible. If not, a déjà vu realization occurs. And so to quote Akira O’Conner again,

For the vast majority of people, experiencing déjà vu is probably a good thing. It’s a sign that the fact-checking brain regions are working well, preventing you from misremembering events. In a healthy person, such misremembering is going to happen every day. This is to be expected because your memory involves millions and billions of neurones. It’s very messy!

Some interesting studies of lab-induced déjà vu

(1) Creating a memory under hypnosis: in this study, memory group researchers from the Leeds University created a laboratory analogue of déjà vu using hypnosis. They had two groups, one of which completed a puzzle game and received a posthypnotic amnesia suggestion to forget the game. The second group didn’t play the game but was given a posthypnotic suggestion that the game would feel familiar. 83% of participants from both the groups passed their respective suggestions but interestingly, more in the second group felt a sense of déjà vu, feeling confused about the source of that familiarity. They also did another experiment with different word cards and hypnosis and the results were interesting where people felt a sense of familiarity towards words they were not shown before and had a sensation of déjà vu.

(2) Déjà vu using virtual reality Sims Game: This study by Cleary et al. (2012) used virtual reality game set to induce an artificial sense of déjà vu. The study included a couple of scenes purposefully created to spatially map one another (as shown in the image below). As a result, many participants mentioned feeling a contrast of familiarity and newness and couldn’t recall the ‘exact’ memories which resulted in a sensation of déjà vu.