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Brain Injuries

Why do brain injury survivors experience déjà vu?

Around two-thirds of people have experienced déjà vu (French for "already seen") where you have a feeling that an event that is happening right now has already happened before. You can feel like maybe you've gone back in time just for a minute, or that perhaps you had glimpsed into the future before now and only just realised. It's a phenomenon that scientists know very little about, but it is clear that it occurs more often in those with a brain injury than those with a healthy brain. Therefore, we can most likely accept that déjà vu is your brain making a mistake and having a moment of confusion.

The temporal lobe helps us store memories, so déjà vu is likely to be connected to the function of that part of the brain

Listen to our Podcast, Brain Injury Bites: Memory problems after a brain injury

Memory helps us make sense of the world around us. If something is new and we don't understand it, we will be cautious or anxious as our bodies prepare for either "fight or flight mode" to keep us safe if it turns out that this new thing is dangerous. However, if we recognise it and understand how to handle it, we can be more at ease. Our brains develop neurons when we familiarise ourselves to something, so we don't have to constantly live on the edge of "fight or flight mode".

It's thought that déjà vu is when these neurons responsible for familiarity, fire at the wrong time, thus giving us the feeling that something has happened before when it hasn't. I think that might be why brain injury survivors experience it more than others. We often have gaps in our memory, or at least it seems to be a bit jumbled up. The brain's memory filing system is not as complete or organised as it was before the injury, so it's grasping for things and making the odd hasty error.

Here's my analogy to help explain what happens:

Imagine you are looking for a person's file in a filing cabinet which hasn't been well maintained and it's a bit messy. Your person is called 'John Smith', and you're trying to be quick, you don't want to keep this person waiting too long. You breathe a sigh of relief when you find a file with the name 'John Smith' on it, and then go to continue the work you needed the file for. But hold on, 'John Smith' is a common name, and so you have accidentally attached the wrong file to the wrong individual as you didn't check their date of birth. You decided it was the right file using one common detail, the name.

When you experience déjà vu, your brain could be taking one detail which might be similar to an existing memory, like a smell perhaps, and fires the familiarity neurons for it. But rather than you just feeling like you know that smell, the whole event feels familiar.

Déjà vu doesn't mean you need to worry about your brain unless it's happening a lot

As I've already said, déjà vu is very common, so I don't want everyone to suddenly start worrying when anyone tells them that they have just experienced it. However, if you are experiencing it a few times a month or more, you should speak to a doctor about it as in a small number of cases it could be a sign of a brain injury, epilepsy or dementia.


Nothing in this blog should be taken as providing medical advice or recommendations. Please always consult your doctor for medical advice and before taking any medication or supplement. Any opinions expressed in this article are of the author and not CFG Law Limited.

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