MANY people are familiar with the brief but intense feeling of a situation [or scene] that they have experienced at some point in the past. Déjà vu usually lasts only a few seconds, yet in that short time, it can disrupt our sense of time, memory and reality.
Although déjà vu is mentioned in popular culture as a mysterious phenomenon, cognitive research helps demystify it by offering an empirically grounded, yet no less fascinating, explanation.
The term déjà vu originates from French and literally means “already seen.” However, according to Vytautas Jurkuvėnas, associate professor at the Institute of Psychology at the Faculty of Philosophy, Vilnius University in Lithuania, the term may be misleading: “In cases of déjà vu, we have not necessarily seen or experienced something before; rather, we experience a sense of familiarity without an actual memory. A feeling arises that the situation is familiar, yet at the same time we clearly understand that we do not remember the event itself.”
Jurkuvėnas explained that déjà vu is neither an echo of past lives nor a
contact with a parallel reality. It is a brief mismatch between several brain systems that work together every day to construct the reality as we experience it.
Most of the time, this cooperative process goes unnoticed; however, occasionally different mechanisms generate conflicting information. It is precisely at such moments that we experience déjà vu.
“Déjà vu is often described as a ‘memory error,’ but that characterization is overly simplistic. Our brains are not designed to function like a computer that precisely records, stores, and retrieves information,” Jurkuvėnas said.
Human memory is imperfect, [and] it was never meant to be perfect, he noted.
“Memory evolved as a system whose primary goals are efficiency, speed, and the ability to predict. Therefore, our cognitive system operates probabilistically: it is usually highly reliable, yet occasional low-probability mismatches are unavoidable.
“In this context, I would not be inclined to call déjà vu an error or a flaw. Rather, it is a feature of our cognitive system. It reveals not a weakness of memory but the complexity of the entire system. If our memory functioned the way computer memory does, it would require far too many resources. Over the course of evolution, what developed was not maximum accuracy but a more flexible mode of operation,” Jurkuvėnas said.
This probabilistic principle of operation becomes especially clear in another key feature of the cognitive system — constant prediction.
According to Jurkuvėnas, the brain is continuously trying to anticipate what will happen in the next moment, in a few seconds, or even in the more distant future. This occurs both consciously and subconsciously and serves a highly practical function: it allows us to conserve biological resources and adapt to our environment more efficiently.
This mechanism is particularly evident in language. When listening to a sentence, we do not passively wait for the next word; instead, we constantly predict it. We anticipate everyday situations in the same way — images,
human behavior, and surrounding circumstances, Jurkuvėnas said.
Déjà vu may occur when this predictive system generates a powerful signal of familiarity. The situation feels as though it has already been recognized by the brain, even though it has not been experienced before. As additional information becomes available, the brain detects that the prediction does not match reality — a mismatch arises between what was expected and what is actually happening.
Importantly, in such cases, another cognitive system rapidly evaluates this
discrepancy. In the absence of other neurological disorders, the brain usually quickly recognizes that the initial prediction was inaccurate and adjusts perception accordingly.
For this reason, déjà vu is typically very brief and has no long-term consequences.
Although déjà vu can occur in entirely ordinary situations, its likelihood increases under certain conditions. Tiredness, stress, or lack of sleep amplifies what is referred to as “noise” in brain systems — the unavoidable inaccuracies in information processing inherent to biological systems.
Neurons never transmit information with perfect precision; however, under normal conditions, these minor discrepancies are constantly corrected. A large part of the cognitive system’s work is specifically devoted to controlling this noise: suppressing irrelevant signals, correcting errors, and structuring information.
Sleep plays a crucial role here — one of its functions is to optimize memory systems and reduce the noise accumulated during the day.
When a person experiences insufficient sleep or prolonged stress, the efficiency of these mechanisms declines. The system of suppression or inhibition that coordinates the activity of different brain processes becomes weaker. As a result, mechanisms responsible for familiarity, memory retrieval, and verification may more easily fall out of synchrony, increasing the probability of experiencing déjà vu.