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What is the view on déjà vu?


Woman scratching head, thinking

Credit: iStock

You’ve experienced it; you are in the middle of a conversation and then suddenly you realise that you’ve been there before. No, it’s not that your sister-in-law is going through the same new-boyfriend problem that she has had for the past eight years, you genuinely feel as though you have been in this exact same place and have had the same experience on another occasion even though you logically know that it is not possible. Is this proof that we exist in multiple dimensions simultaneously and your other selves are for an instant breaking through the space-time continuum to communicate to you? Is it a past-life experience somehow replicated in your current circumstances? Or is it, less excitingly, a glitch in your brain?

Unless a researcher was to find someone willing to be strapped continually to an EEG or spend their life in an MRI machine, then you can't find out exactly what is happening in the brain when déjà vu occurs. However, as researchers have done in a new report, you can make some educated guesses.

The experience we are describing here is commonly known as déjà vu from the French for “already seen” and it is estimated that somewhere between 60 and 80 per cent of people experience it at least once. It is a very difficult phenomenon to study because you only know it has happened retrospectively and it happens rarely. Unless a researcher was to find someone willing to be strapped continually to an EEG or spend their life in an MRI machine, then you can’t find out exactly what is happening in the brain when déjà vu occurs. However, as researchers have done in a new report, you can make some educated guesses.

One theory about déjà vu is that it is related to memory. The temporal lobe of the brain is where you make and store long-term memories. We also know that people who suffer temporal lobe epilepsy (a condition in which nerve cell activity is disrupted causing seizures) also report experiencing déjà vu as a warning of imminent seizures. The researchers suggest that in healthy people déjà vu might be a kind of neural “glitch” where the neurons involved in memory fire encouraging the brain to mistake the present for the past. This is believable because abnormal electrical impulses can be present in healthy people as seen in the “hypnogogic jerk” or involuntary muscle spasm that occurs as a person is falling asleep.

Another theory is that déjà vu arises because the brain is constantly trying to create whole perceptions of the world in which you move but with limited input. So, for instance, only a familiar smell is enough to create recall of a detailed memory. Déjà vu may result if a glitch leads to sensory information bypassing short-term memory and triggering long-term memory instead, producing the unsettling feeling that you have experienced a new moment before. Alternately, sensory information travels along a number of neural pathways to the higher portions of the brain (cortices) and if two separate messages Travel at different speeds then the slower input is experienced as a separate perceptual experience it creates that feeling of familiarity that we call déjà vu.

So we have some theories but no definitive causality for déjà vu: wow, it feels like we’ve been here before.



 

Terry Robson

Terry Robson is the Editor-in-Chief of WellBeing and the Editor of EatWell.