Why does Déjà Vu Occur?


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You know that moment when something happens when you all of a sudden realize "Wait, this has happened before," well that's déjà vu! 

Déjà vu can be better described with a Merriam-Webster dictionary definition.


dé·jà vu

a : the illusion of remembering scenes and events when experienced for the first time
b : a feeling that one has seen or heard something before


The concept of déjà vu, thinking that a moment has happened or occurred before, is difficult to scientifically study because there is no reliable way to cause it to happen and therefore difficult to study in a lab. According to studies, as much as 70% of the human population claimed to have experienced some form of déjà vu at one point in their lives. The highest numbers of incidents occur in individuals of the ages of 15 to 25 years old than at any other age. It was discovered that déjà vu doesn't appear until 8 to 9 years of age in children, peaks from early 20's to young adults, and slowly happens less frequently the older we get. These correlations suggest that déjà vu is connected to brain development yet scientists have several different theories on why it occurs. One of the predominant theories and most of the theories include an explanation that there is a disconnect that may be occurring within the deeper structures of the brain that process and interpret our memories and experiences unconsciously and consciously. So the conscious and unconscious parts of the brain are in discord. Memories, experiences are differently interpreted through sight, memory, etc.


Let's first observe the visual system in which the brain interprets experiences. When you visualize something or have an experience, you're eyes are the ones who capture it and send the message and what it's seen through the brain to the back of the brain known as occipital lobe where the visual cortex is. The visual cortex in the occipital lobe is where the information that we see is finally processed by the brain and where the interpretation of what we're seeing makes it way to visual to conscious. Thing is though, this information's last stop is to the occipital lobe where the visual cortex interprets it and there are prior stops that this information stops at. One of the other stops are the amygdala that centers and concentrates on triggering and focusing on emotion, learning, and memory especially involuntary emotional reaction. Next is the tecta that is the primary visual interpreter and also controls eye movement.


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 These two stops are important because individuals who are visually impaired have damage within the visual cortex of the brain in the occipital lobe. What's odd though, is that even though they can't visually see an object, they still can sense objects. A few examples of these are if you put obstacles on the floor, blind individuals can sense it, and move around it and also if you show blind individuals a picture of a person smiling or frowning on the screen, they can sense it and can respond back with that expression the person has on the screen!!! This phenomenon is considered as blindsight. It's odd that even though the visual cortex is damaged and an individuals cannot visually see, there's a stop that those neural messages make in which the images a blind person sees can still be interpreted in the brain.


It's suggested that while going through this process of making stops, by the time it goes through the amygdala and tecta, and reaches the visual cortex, there's a disconnect in which the visual cortex doesn't completely grasp a certain experience or visual that makes it think, "Wait. Haven't I seen this before?" It happens when these "stops" get out of sync. This out of sync occurrence can be caused by a neurological abnormality where there is a temporal-lobe epileptic episode that causes the disruption in the process of interpreting visual interpretation. To prove this, studies show that people who are more likely to experience déjà vu, sometimes chronic and persistent,  have more damage in the temporal lobe of their brain.

Though this sounds very dangerous, epileptic episodes in your brain are quite common and also known as the common term hypnagogic jerk. A hypnagogic jerk can easily be described as the moment you are about to fall asleep and your body suddenly jerks. Going slightly into the reason for hypnagogic jerking is that when you sleep your body relaxes and a part of your brain thinks "HEY! You're unaware, you must be falling and so your brain sends a signal to your brain so that all your muscles twitch, waking you up.

So next time you have déjà vu, your brain is just probably having some epileptic episodes! No big deal!

It's been most closely studied in epilepsy, where patients often experience it before a seizure. The brain regions for memory are in the temporal lobes, and there's an area for monitoring memory accuracy in the middle frontal lobe. Those patients reporting déjà vu are temporal lobe seizure patients. The actual trigger for it in healthy individuals is not exactly known, but we do know those same regions of memory and memory monitoring are involved."

Read more at: http://phys.org/news185192263.html#jCp
It's been most closely studied in epilepsy, where patients often experience it before a seizure. The brain regions for memory are in the temporal lobes, and there's an area for monitoring memory accuracy in the middle frontal lobe. Those patients reporting déjà vu are temporal lobe seizure patients. The actual trigger for it in healthy individuals is not exactly known, but we do know those same regions of memory and memory monitoring are involved."

Read more at: http://phys.org/news185192263.
It's been most closely studied in epilepsy, where patients often experience it before a seizure. The brain regions for memory are in the temporal lobes, and there's an area for monitoring memory accuracy in the middle frontal lobe. Those patients reporting déjà vu are temporal lobe seizure patients. The actual trigger for it in healthy individuals is not exactly known, but we do know those same regions of memory and memory monitoring are involved."

Read more at: http://phys.org/news185192263.html#jCp
It's been most closely studied in epilepsy, where patients often experience it before a seizure. The brain regions for memory are in the temporal lobes, and there's an area for monitoring memory accuracy in the middle frontal lobe. Those patients reporting déjà vu are temporal lobe seizure patients. The actual trigger for it in healthy individuals is not exactly known, but we do know those same regions of memory and memory monitoring are involved."

Read more at: http://phys.org/news185192263.html#jCp

2 Comments

I've always wondered if déjà vu was one of those things that couldn't be explained. Finding out that it's just an epileptic episode is very disappointing! I think finding out new things about the human brain is fascinating and delving deeper into this subject would definitely be worth reading about.

What a great post. I've always wondered what causes deja vu; your explanation was great.

I think one of the most interesting parts of your post is about the hypnagogic jerk, which is something I experience all the time. I've always had a hard time falling asleep and I feel like, often times, I'll be right on the precipice of falling asleep and then my brain just screams "WHAT ARE YOU DOING?! WAKE UP!"

I'm not sure if a hypnagogic jerk is the same as a hypnic jerk (I'm assuming they are). I was able to find a lot of good information about hypnic jerks, including this article from the BBC Futures section: http://www.bbc.com/future/story/20120522-suffer-from-sleep-shudders

It says in the article that hypnic jerks do not represent what the actions that we are doing in our dreams (ex. if you are dreaming about riding a bike, your legs will not actually be moving).

I'm not sure if I agree with this. Maybe that action of doing in your sleep what you think you're doing in your dream is defined by a different term. I know I've had dreams before where I do this. I had a dream once that I was throwing a softball, and I woke up because I thrust my arm in my sleep off my bed and knocked my alarm clock to the floor. On that same note, I've seen my dog "run" and "bark" in his sleep, as if he was chasing an animal. Does anyone have similar experiences/thoughts on this topic?

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