Put your hand up if you’ve ever experienced a flicker of puzzling recognition as you do something. Whether that be petting a dog, watching a film, or even entering a house you know you’ve never been in before.
The puzzling psychological phenomenon that is déjà vu is a sudden sensation that is often short-lived. It implies that you’ve experienced your current situation before, and are recalling it vividly, even when you’ve never experienced it. déjà vu.
That ‘I’ve been here before’ sensation.
That creepy feeling that often leads people to rationalise the sensation of familiarity as the memory of a past life.
But no… déjà vu is due to something else.
Déjà vu is seen as a psychiatric oddity that’s extremely common, occurring in about 60% of the world’s population. Understanding how déjà vu works sheds light on the function of human memory and our complex brains.
This sensation has always been associated with a slight air of confusion, strangeness and mystery. The term originated in 1876, when a French philosopher and paranormal investigator named Emile Boriac coined the term in a letter. It has fascinated psychologists, scientists and artists ever since. Freud hypothesised it was prompted by repressed desire , while the makers of the Matrix trilogy made the feeling a sign of a ‘glitch’ in the artificial world. But the truth might actually be stranger than fiction.
The Many…Many Theories
Understanding déjà vu means delving into neurology and human memory, and over the years, scientists have developed many possible explanations for the phenomenon. In fact, there are over 40 theories that have been hypothesised.
In a review of the science, the Psychological Bulletin outlined four major schools of thought about why déjà vu may happen. The first theory is the most simple. The theory suggests that the event has already happened, and for some reason you had forgotten this and déjà vu is the process of your brain reminding you. The second theory is that déjà vu is brought about by a processing error in the brain. Where two elements are trying to operate simultaneously and something misaligns.
The third notion is called the ‘disruption’ theory. This is where neural firings in the brain are somehow interrupted. It’s argued that this is why people with epilepsy experience déjà vu as part of the perceptual disturbance of their seizures. For people without epilepsy, the theory states that the brain accidentally overlaps the current experience which gives the sensation that the event has already happened.
The fourth theory is called the ‘attentional’ explanation. While you might be paying attention to your surroundings, it suggests that you might become distracted for a split second. Then, when you refocus, it may seem oddly familiar in a ‘past’ way.
An interesting point about déjà vu in epileptics is that it is most strongly related to medical temporal lobe epilepsy. This affects the brain’s hippocampus, which is essentially where your memories are stored. This is a good boost to the theory that misfirings in the brain is behind the experience of déjà vu itself. However, epileptic and non-epileptic déjà vu seem to differ. When it comes to déjà vu not related to epilepsy, scientists have also found that stimulating another area of the brain, called the entorhinal cortex, can induce it. This part of your brain also helps to store memories.
So, what’s actually going on?
The Latest Findings …
Despite all of the coverage in popular culture, experiences of déjà vu have been poorly understood in scientific terms. However, a team from the University of St Andrews in the UK has found evidence that déjà vu is a failure to separate: a mistake of the brain to make sure a new memory isn’t interfering with an old one. It usually occurs when you think you recall something but you can’t quite place it. It’s a little bit like having a word on the tip of your tongue.
Even more interestingly… researchers have been able to recreate the feeling in a lab setting. They do this by creating scenes that are laid out identically, but with different scenery. For example, a retail store arranged just like a bedroom you’ve already seen. So with a clothing display where the bed used to be. Researchers use something called functional magnetic resonance imaging (fMRI) to observe the participants brain activity. They found that the most active regions of participants’ brains, were not the parts of the brain the brain used to store memories. Instead, the frontal areas, which are typically involved in decision-making, were activated during the déjà vu experience. So this means your brain is using it’s decision-making functions to fact check your memories.
It’s remarkable that we don’t experience déjà vu more often. Given that we live an average of 70 years. We experience around 2,207,520,000 seconds in our lifetimes. We make memories throughout this time, often down to the scale of only a few seconds. It’s likely that we store millions of new memories and yet a mere handful accidentally turn up in the wrong place.
Be sure to give thanks to pattern separation when you remember your wedding and not every wedding you’ve ever been to. And be thankful when you remember the first day of your dream job and not every office you’ve worked in. Happy memories. Separate memories.