"It's like déjà vu all over again." ~Yogi Berra.
I am writing this because when I sat down to work out what to write, I got an overwhelming sense that I had been in that exact moment thinking those exact thoughts previously, although I knew I hadn’t! Experts would call that déjà vu (French for ‘already seen’) defined as not only a sudden fleeting feeling of familiarity, but also the recognition that the feeling is incorrect.
An estimated 60-70% of us experience déjà vu, and it most often occurs in a healthy brain. However, it is also a well-known association of epilepsy, when disruption of electrical signals occurs in the temporal lobes. The temporal lobes have an essential role in memory, and parts of the temporal lobe also play a role in recognizing something as familiar. Hence déjà vu has been understood as a memory related phenomenon - an illusion of memory. Other explanations of déjà vu have suggested momentary mix-ups of cognitive processes, such as immediate or short-term memory mistaken for long term memory, or attention mismatch – the brain perceiving something before you pay conscious attention to it.
However, there is no single agreed upon model that explains exactly what happens in the brain during déjà vu, partly because the phenomenon is unpredictable and hard to study. Recent theories and fMRI favor the idea that déjà vu occurs when memory areas of the brain (esp. the temporal lobes) inform frontal brain regions (medial prefrontal and anterior cingulate cortex) that an experience is repeating itself. The frontal decision-making areas of the brain then check to see whether this is consistent with what is possible, for example by seeing if there are other related memories available. If not, a déjà vu happens, and it is a sign that your fact-checking brain regions are working well and correcting inaccurate memories.
Most healthy individuals experience déjà vu a few times a year. However, several factors can change that frequency, such as increased occurrence in times of stress and fatigue when neuronal systems haven't had the chance to recuperate and may experience more misfiring. On the other hand, aging leads to decreased déjà vu experiences – perhaps because, like other memory issues, older brains are less able to fact-check memories and notice errors.
An interesting phenomenon related to déjà vu is déjà vécu (French for 'already lived'). These are cases of people who suffer persistently from the constant sensation of having already experienced the present. To them everything feels like a rerun. This can happen in dementia patients who seem to have lost the capacity for correcting memory mix-ups. Those affected will give up reading or watching TV as nothing seems new, and it is often very disconcerting to them.
And then there is jamais vu (French for ‘never seen'). This means failing to recognize a situation that should be familiar. Like déjà vu, this also happens in healthy brains as well as in association with temporal lobe epilepsy. Although often associated with amnesia, jamais vu is not a mere memory lapse. It’s a disorientating feeling that you don’t recognize something when you know you should, and that the feeling is wrong. Interestingly, experiments seem able to prompt jamais vu in participants just by using repetition. One study asked people to write the word ‘door’ as many times as possible within two minutes. After a minute or more, 70 per cent of the participants experienced doubt whether the word door was spelled correctly, or even if it was a proper word at all. Although the mechanisms are not understood, one favored scientific explanation is that repetition in a perceptual act like reading a word somehow overloads its representation in the brain until it becomes dissociated from higher-level processing and stops making sense. Jamais vu may act as a signal that something has become too repetitive, and the accompanying feeling of disbelief prompts us to reassess the situation at hand.
For me, these seeming quirks highlight how well our brains work most of the time. All our experiences come out of finely tuned and smooth interactions between our perceptual and cognitive systems, and we vigorously defend their veracity. When déjà vu and jamais vu happen, they are reminders that we are sometimes mistaken and need to take corrective measures.
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Post by: Nadia Fike
Read More: 1.O’Connor A. R., Moulin C. J. Recognition without identification, erroneous familiarity, and déjà vu. Curr. Psychiatry Rep. (2010)12 165–173. 2. Urquhart, J.A. (2021) fMRI evidence supporting the role of memory conflict in the déjà vu experience. Memory (2021) Aug;29(7):921-932. doi:10.1080/09658211.2018.1524496. Epub 2018 Sep 20
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