Why your deja vu could be a sign of this terrifying hidden condition - as top scientists reveal who is most at risk
Experiencing the very occasional bout of deja vu is not uncommon – nearly everyone has had it: that sudden overwhelming feeling that you’ve previously experienced exactly what’s happening right now, with everything exactly how you remember it, in vivid detail.Or it’s that sense that you already ‘know’ what someone is going to say next – maybe even that you’ve read this article before...But of course you haven’t.Most of us who have experienced deja vu are entirely healthy.But studies suggest people who experience it persistently have a potentially increased risk of health problems, such as epilepsy, heart disease and dementia, or a psychotic mental disorder.Reports vary on the prevalence of deja vu, with estimates saying that anything from 60 to 97 per cent of people have experienced it at least once in their lifetime, with around two-thirds of deja vu-ers saying they experience it quite regularly.The phrase comes from the French, and means ‘already seen’. Yet you haven’t ‘seen’ it: your brain is playing a very common trick on you. What’s more, deja vu is not the only mysterious memory glitch we can experience.Other bizarre types can make people suddenly believe that a familiar thing is actually totally new (jamais vu); or that they are re-enacting in real life a dream they’ve had (deja reve); or they can predict what will happen next or think they are familiar with places they have never been before (deja entendu) – but more on these later.For hundreds of years scientists have tried to pin down what exactly causes these strange mental experiences. Deja vu has been most frequently studied in the brains of patients with epilepsy, primarily because they may experience it much more predictably – during an epileptic episodeThe most recent attempt came in May, when researchers at Yale University suggested that deja vu may be the result of people experiencing ‘hyper-recency’.This is where the brain inserts our present experiences straight into our memory at the same time as they are happening, producing the eerie sensation of ‘hang on, I remember this’ just as events are occurring for the first time.In a study published in the Journal of Experimental Psychology: General, involving 500 volunteers, the researchers found that people whose psychological profiles show higher levels of psychosis (such as irrational fears and confused thinking) said that they are more likely to experience ‘hyper-recency’ and deja vu.This echoes another study, based on 936 participants, which showed that experiencing very frequent deja vu is a particularly strong sign of high clinical risk for psychosis, reported the Brazilian Journal of Psychiatry in January.In fact, over the years scientists have suggested a myriad other explanations for how and why we can experience the been-here-before sensation.In his 2004 book, The Deja Vu Experience, Alan Brown, a professor of psychology at Southern Methodist University, suggested that 30 different brain mechanisms are involved – and that any one of them alone may be enough to trigger a deja vu experience.Deja vu has been most frequently studied in the brains of patients with epilepsy, primarily because they may experience it much more predictably – during an epileptic episode.In December last year neurologists at the University of Louisville studied the brain patterns of a 19-year-old woman who frequently had deja vu during her seizures, and reported that these experiences appeared to be generated from the medial temporal lobe, a key brain area which houses a number of structures involved in memory processing, such as the hippocampus and amygdala. Christopher Moulin, a professor of cognitive neuropsychology at the University of Grenoble in FranceBy stimulating this area with an electrical current, other researchers have been able to trigger the feeling of deja vu in patients with epilepsy.Also within the medial temporal lobe sits the rhinal cortex, thought to generate the sense of familiarity we feel when encountering something already known to us.The temporal lobe is also associated with regulating blood pressure and heart rate – and this is why people who experience frequent deja vu may also have an increased risk of cardiovascular disease, according to surgeons writing in the journal Current Problems in Cardiology in 2023.They said: ‘One theory suggests that deja vu may be a result of a disruption in the temporal lobe, which is also responsible for regulating blood pressure and heart rate. Another theory suggests that there may be a shared genetic factor between the two conditions.’The report said that the genetic link behind this might be the APOE gene, which is linked to heart disease for its role in carrying clot-forming blood fats and cholesterol that are characteristic of cardiovascular problems.The gene is also associated with memory processing – so it might somehow be implicated in the mental-processing glitches that prompt deja vu, the researchers from East Lancashire Hospitals NHS Trust said.Intriguingly, the APOE gene is also associated with Alzheimer’s, and a separate study published in the journal Psychiatry Research Case Reports last year reported that deja vu is an under-reported and troubling experience in people with the disease.But deja vu is not the only memory glitch that can affect our lives in bizarre ways. In fact, it has a mirror-image opposite: jamais vu (French for ‘never seen’).‘Jamais vu may involve looking at a familiar face and finding it suddenly unusual or unknown,’ says Christopher Moulin, a professor of cognitive neuropsychology at the University of Grenoble, France.He has asked people to describe jamais vu in questionnaires about experiences in daily life: ‘They give accounts like: “While writing in my exams, I write a word correctly like ‘appetite’ but I keep looking at the word over and over again because I have second thoughts that it might be wrong”,’ he says.In 2021 in the journal Memory, he led an experiment which showed that jamais vu can be quite easily induced in people.‘If you just ask someone to repeat something over and over, they often find it becomes meaningless and confusing,’ he explains.In his tests he asked 95 volunteers to keep writing words such as ‘the’, ‘door’ and ‘sward’. After about a minute the volunteers tended to stop, saying they felt strange.‘People described their experiences as ranging from “the words lose their meaning the more you look at them” to “seemed to lose control of hand” and – our favourite – “it doesn’t seem right, almost looks like it’s not really a word but someone’s tricked me into thinking it is,” Professor Moulin says.Another disconcerting memory glitch involves having the uncanny conviction that you have already dreamt about something that is now happening in your waking day – it’s called deja reve (‘already dreamed’ in French).Once again, the mechanism for this eerie sensation seems to be located in the brain’s temporal lobe.In a study published in the journal Brain Stimulation in 2018, researchers at Toulouse University Hospital in France tried using electrical stimulation to find which parts of the brain were involved in epileptic seizures.What they found instead, however, was that stimulating the temporal lobe could produce a deja reve experience in some patients.One said that while awake, they re-experienced a nightmare from years ago – while another claimed she was taken back to a recent dream where she was locked in a room and could vividly see orange colours.As well as quite literally feeling that one is ‘living the dream’, matters can get even more eerie with another manifestation of memory glitches – feeling as though you can predict the future, a phenomenon that psychologists call deja entendu (‘already understood’).As neurologists and psychologists, writing in the journal Memory & Cognition in April, explained: ‘Deja vu is often accompanied by an illusory feeling of knowing what is about to happen next.’ There have been case reports of people who experience deja entendu saying they feel suddenly convinced that they already know how to navigate towns and cities where they are newly arrived, or they switch off TV programmes halfway through because they are sure they know what happens next, even though the programmes are new to them.Read More All the celebs who are YEARS younger than you think... surgeons know the shocking reason why Is there any truth to these apparent clairvoyant abilities?Not according to the report in the journal Memory & Cognition – the US researchers tested patients who experienced bouts of deja entendu by asking them to predict what notes would come next in previously unheard piano recitals.The participants’ confident predictions proved no more accurate than ordinary guesswork.Lastly, if you find yourself desperately trying to remember the names of all of these different types of weird memory glitches, but just can’t quite manage it, you might find yourself suffering a bout of presque vu (almost seen).This describes the maddeningly frustrating ‘tip-of-the-tongue’ feeling that occurs when you are trying desperately to recall something, such as a famous actor’s name – and it feels just out of reach.The good news is that this one may not actually be an illusion.A 2015 study by Missouri State University reported how researchers asked volunteers to play a series of games where they had to recollect specific words.They found that when participants reported feeling presque vu, they were likely to arrive at the correct answer a little while later.As the study concluded: ‘Presque vu may indicate impending retrieval of as yet unretrieved relevant information.’So the answer is to just keep trying, because the answer really may be on the tip of your tongue.Or does it seem that you knew that before anyway?
