Out of all of the organs, the human brain is the most complicated and one of the least understood. It’s responsible for all of our behaviours, thoughts, feelings, processes — everything that makes us human. That’s one of the many reasons I find the brain and neuroscientific research so fascinating, and why so many scientists study it!
Sometimes our brain does funny things, almost like it’s glitching. When you walk into a room and suddenly completely forget why you walked in there (the "doorway effect"), open the fridge and stare blankly at the contents for no apparent reason (the most likely boredom effect), or when you feel like you have had this exact experience before, despite knowing you haven’t. Sound familiar? That’s because it is!
That "strange feeling that in some way you have already experienced what is happening now", even though you know logically that you couldn’t have, is the eerie phenomenon known as déjà vu, literally French for "already seen". Lasting briefly, only for a few seconds, déjà vu is an overwhelming sensation of familiarity, where we feel like we’ve already been in the specific situation we’re in. It is such a strong short-lived feeling but incredibly odd in the sense we are aware that we couldn’t have possibly previously had this experience. But why does this happen? Do we all experience déjà vu? And why does it feel so weird?
Déjà Vu Out in the Wild
Déjà vu as a concept has been around for over a century. French philosopher, Émile Boirac, was one of the first people to use the term, back in 1876. Since then, déjà vu is much more common in our everyday lives, having taken on new meanings, infiltrated pop culture, and eluded researchers trying to pin down its origin. With roughly 60% of people experiencing déjà vu at some point in their lives, it has solidified itself as a mysterious and bewitching brain blip, spurring speculations of us living in a simulation.
With several songs titled after it, most notably by Beyoncé, Dionne Warwick, and Olivia Rodrigo (which I was only slightly obsessed with a couple of years ago), déjà vu is often linked with past memories and dreams of a significant other, something almost ethereal and magical. But it’s also used in a different manner by Rodrigo to ask her former partner if he experiences déjà vu with his new partner, since everything they’re doing together is "recycled" from his relationship with Rodrigo.
Plenty of movies and TV shows also play on the concept, intertwining it with time travel, dreams, and enthralling science fiction: Groundhog Day (and the countless modern variations), The Matrix, The Truman Show, Inception, and even one titled after ‘Deja Vu’, featuring Denzel Washington as a federal agent, who uses a device to look four days back in time through a time warp to try and prevent a terrorist attack.
When conducting a search on PubMed, a free search engine used to access scientific articles, and sorting the results by most recent, I found that even scientists use the term déjà vu in the titles of their papers when revisiting specific research topics. It can definitely draw attention to the article and makes the title a little spicier, as in to say, "Have we been here before"’ and stress the importance of the area addressed. Examples from this year alone range from Monkeypox to dangerous dogs to P-CABs (Potassium-competitive acid blockers — drugs for acid reflux).
The Neuroscience Behind Déjà Vu: How Does it happen?
Like many brain-related experiences, there isn’t one single explanation for déjà vu. It’s really difficult to record and study déjà vu as a scientist, due to its sudden and fleeting nature. Since it is always described retrospectively as a ‘sensation’ or ‘feeling’ by study participants and there are no physical manifestations of déjà vu, it has been challenging for scientists to recreate it in the lab or determine one conclusive cause.
There are over 40 theories attempting to decode déjà vu. Most of the theories share a similar idea, that déjà vu happens when parts of the brain tell us that a past experience is repeating itself. The four most prevalent theories are:
Attentional: suggests when our attention is divided, we take in environmental information subconsciously, so that when we return to full awareness and pay attention, we feel we have seen it all before, resulting in déjà vu.
Dual-processing: suggests that when our brains are processing information, two cognitive processes which are usually in sync become briefly asynchronous, so there is a slight delay resulting in us interpreting the late information as a separate event, hence déjà vu (e.g. familiarity and retrieval could become uncoordinated).
Neurological: suggests that déjà vu is a manifestation of neurological dysfunctions, involving small seizures or changes in the timing of communication between brain cells (neuronal transmission).
Memory: suggests that during déjà vu, our situation is objectively familiar, but we have forgotten the reason why it’s familiar, as if our brain is trying to retrieve a deep and distant memory by checking against our past experiences but there is no recollection of it, leading to that uneasy feeling — this can be triggered by a very small amount of sensory information, like a distinctive smell that we recognise.
The formation and retrieval of memories, including auditory ones such as music, takes place in an area of our brain called the temporal lobe. It encases the hippocampus (learning and long-term memory formation) and the amygdala (the emotion processing centre), and is also seemingly responsible for integrating memories with our senses: taste, sound, sight, and touch. Those who have suffered temporal lobe epilepsy, seizures caused by disrupted brain cell activity, have reported experiencing intense déjà vu before seizures, reflected in clinical reports. In these instances, déjà vu acts as a forewarning of an epileptic seizure event.
It has also been suggested that dopamine, "the Kim Kardashian of molecules" (as dubbed by British clinical psychologist, Vaughan Bell) and happy hormone, may be involved in the experience of déjà vu. Our temporal lobes are also responsible for discerning familiarity, and dopamine is an excitatory neurotransmitter or brain chemical involved in this process. This could potentially explain why we experience déjà vu more often when we take dopaminergic drugs, which increase our dopamine levels.
Who Experiences Déjà Vu?
If you’re constantly tired or stressed (same), you’re more likely to experience déjà vu as fatigue and stress impact our memory, which is a potential cause of the phenomenon. When you’re fatigued, your brain doesn’t have sufficient time to regulate, so you’re more likely to have incorrect or uncoordinated cognitive processing.
Young people are also more likely to experience déjà vu than the older population (sorry if you’re young and tired and stressed), supporting a theory which suggests that our brain cells randomly misfire. The younger your brain, the higher the level of excitatory activity taking place. One of the most consistent findings relating to déjà vu is that as you get older, you’re less likely to experience déjà vu. The frontal part of our brain which fact-checks the information we are processing becomes a little less efficient with age, as it’s less able to notice errors.
Sometimes our brain does funny things, almost like it’s glitching. Wait! Sorry.
The next time you experience déjà vu, remember that it’s a totally normal human thing, and we don’t really know where it comes from just yet!