English Version | Been there, done that

It’s a weird sensation, it can even be breathtaking: the feeling that a particular moment has happened before. It’s probably one of the biggest mysteries of the human psyche, deja vu has been the study subject by the scientific community that attempts, at every instance, to unveil it. 

I don't remember exactly the first time I had a déjà vu sensation, but I do know that when it happened, I had no idea what was going on in the back of my mind - but what a bizarre episode it was. Later, when trying to explain to someone what it had felt like, and after further déjà vu experiences, I finally knew what it was all about. Knowing, I didn't know, I still don't know. But I knew, at least, that "it" had a name, and that I was not the only one to feel that strange sensation. All because science and psychology have been trying to explain it. The French term déjà vu, in Portuguese "já visto", refers, as the term itself indicates, to a psychological reaction of the transmission of ideas that one has been to a certain place before, that one has seen certain people before, or that one has simply experienced a particular moment in some past. Scientifically, it is estimated that two-thirds of people have experienced an episode of déjà vu at least once in their lifetime. However, there is no unanimity as to a pattern of who is most likely to experience this sensation, nor as to the age at which it is most likely to happen. According to a study by the Cleveland Clinic (United States), about 60 to 70 percent of healthy people have experienced déjà vu, and it tends to be most frequent in the 15 to 25 age group, decreasing with advancing age. "Psychologists cannot explain exactly how the feeling of déjà vu occurs, but there are several theories and hypotheses on the subject, which remains a real challenge for science. The theories are all somewhat complex and, although they point to different mechanisms to explain why déjà vu happens, they all point to an error in the way the brain is processing immediate memory", says Joana Oliveira, psychologist, and psychotherapist at Clínica da Mente.

In an article published in The New York Times about this phenomenon, Alan Brown, a psychologist at Southern Methodist University (USA) and author of the book Essays of Déjà Vu Experience in Cognitive Psychology (2004), wrote: "[the phenomenon] has been ignored or considered scary or even weird to many scientists (...) But it's real, and by bringing it into the laboratory, we can at least try to begin to understand it." Psychologists are still searching for explanations for this event, but in general two theories can be pointed out: the feeling of familiarity caused by the way the memories originated; and the feeling of déjà vu being related to a communication break, momentary, between the conscious and the unconscious mind. Joana Oliveira elucidates: "The 'father of Psychoanalysis', Freud, understood déjà vu as being the result of repressed desires, that is, the sensation plays the role of a defense mechanism caused by a kind of suffering that was repressed. On the other hand, for Jung, and in the light of Transpersonal Psychology, déjà vu would simply be the result of the collective unconscious. Other psychologists, based on Jung's psychology, have linked the phenomenon of déjà vu to active imagination, that is, to the access to memories that have been repressed for the most diverse reasons and that help recover information long forgotten." For Alan Brown, among other scholars of the phenomenon, it is not necessary to invoke hidden conflicts or unusual brain conditions to explain many cases of déjà vu. As stated in that article in The New York Times, normal brain function is sufficient: "Déjà vu appears to be most common when people are exhausted or more stressed, conditions that are known to obscure short- and long-term memory - and that can also accompany 'jamais vu,' the opposite experience of looking at familiar words or objects and having no recollection of them."

Since déjà vu is such an intriguing manifestation, it is only normal that it has been studied by scientists, also in a laboratory context: "It began to be observed that déjà vu occurs in the brain, causing a variation in the cognitive system and leading the person to have the sensation of having already lived that moment, of having gone through that experience, of having been with that person before. These studies stopped relating déjà vu to past experiences and started to understand it as a cerebral, neurochemical reaction. However, even in the case of scientific studies, there is no consensus about how the sensation originates," says psychologist Joana Oliveira. And she adds: "More recent studies have verified that the sensation of déjà vu is a reflex of the brain when analyzing the memory it has just produced. These studies also found that this process activates the frontal region of the brain, which is responsible for decision-making." Other research has understood that déjà vu happens when there is an error in brain processing and the facts that are occurring at the moment do not pass through immediate memory but are directly stored in the medium and/or long-term memory, giving the feeling that that situation, which is happening "here and now", has been experienced before. What occurs is a failure of neuronal communication and a delay in the transmission of information between the conscious and the unconscious, causing the memory to be recorded twice.

The misunderstanding of déjà vu has long been associated with a metaphysical experience, as a kind of preview of the future. But according to most scholars, it is a common and meaningless phenomenon in healthy people: "There is no scientific explanation for déjà vu that is unanimously accepted by the scientific community, but one of the hypotheses is that it is a kind of 'start-up' of the brain, where the feeling of familiarity occurs simply because a situation, a place or a smell reminds us of a particular memory. Researchers have put on the table several other theories: one of them is that there is abnormal signaling in the brain, which makes something never experienced before be perceived as familiar", corroborates neurologist Gonçalo Matias, in an article on déjà vu published in the Hospital Lusíadas website. And he underlines one of the most established explanations, the one based on the fact that there may be a failure in the storage process of memories that causes an overlapping in which recent and less recent events are mixed. On the other hand, there are studies that suggest that when you experience déjà vu, there is an inappropriate activation of the area of the brain associated with the feeling of familiarity. But déjà vu can also be one of the symptoms presented by those who suffer from temporal lobe epilepsy, appearing before an epileptic seizure: "In this disease, any area of the brain can be activated involuntarily and the person may experience physical sensations that they have already experienced in the past, or relive a situation that has been stored in the memory," stresses the neurologist in the text above.

Déjà vu may thus be indicative of a neurological disease when: it occurs frequently (a few times a month or more often); it is accompanied by abnormal memories that resemble dreams; it is followed by loss of consciousness and/or changes such as involuntary chewing, restlessness, increased heart rate or irrational fear. "In these cases, it is important to consult a neurologist so that he can screen for an underlying pathological cause," warns Gonçalo Matias. Psychologist Joana Oliveira recognizes the epilepsy theory: "Among the scientific community, the most accepted argument is that déjà vu originates from a type of mini-epilepsy episode, causing the temporal lobe to stop being in sync with the other cerebral lobes. This happens because immediate memories are quickly sent to the place where long-term memories are stored, giving the feeling that what is happening now has already been experienced in the past. More recently, people have been found to have chronic feelings of déjà vu. Research in this area has found that these people often have the ability to remember specific details about a situation that didn't actually occur, and they can even (have the illusion of) predicting something that is yet to occur. Other explanations considered for déjà vu include anxiety - because, as mentioned above, scientists found that it was more common to occur when the person was going through a stressful time; other studies found that people more prone to déjà vu were those who traveled frequently to different places; or those who have evidence of temporal lobe atrophy. There are also scientists who say that there are common characteristics in people who have the sensation of déjà vu: having a creative mind and a high IQ; and being between 15 and 25 years old (a characteristic already mentioned). Although there are no certainties, what researchers explain in this respect is that, since déjà vu is related to the formation of memories, it is during adolescence and early adulthood that people create the most expressive memories of situations they have lived through. 

Other scientists believe that déjà vu happens more frequently at these ages only because the pleasure hormone - dopamine - is present at higher levels. Psychologists also consider that the decrease of this sensation with age may be due, on the one hand, to the fact that the brain, as the years go by, is able to manage more efficiently its perception of memories in search of possible omissions; on the other hand, Joana Oliveira remarks, "scientists put forward the possibility that the brain, as the years go by, has difficulty recognizing faults." There are also researchers who point to a greater predisposition to déjà vu in people who sleep little and who use drugs that stimulate dopamine activity in the brain - the predisposition to the sensation of déjà vu is potentiated by stress, but also by fatigue, excess alcohol and/or drugs. Due to its complexity, this is a phenomenon that has increasingly aroused the interest of psychologists and neuroscientists. The difficulty in understanding déjà vu is compounded because the sensation occurs so spontaneously that it is extremely difficult to replicate the phenomenon and investigate it in a laboratory setting. Although there is no consistent scientific explanation for the phenomenon, "déjà vu is a sensation that appears occasionally and, in healthy people, is nothing to worry about", assures neurologist Gonçalo Matias. If, however, you get the feeling that you've read this text before, don't be surprised, it's most likely another trick of your brain, this complex but fascinating machine of ours.

Translated from the original on The Butterfly Effect issue from Vogue Portugal, published October 2022.Full story and credits on the print issue.