Why do we get déjà vu? There is a dysfunction in the part of your brain that processes familiarity and a correction by the part that processes memory.
Déjà vu comes from French, and it means “already seen”. It is the feeling that you have already seen or experienced something you are seeing or experiencing at the current time, while knowing at the same time that you haven’t seen or experienced it before. It is the disconnect between the sensation of familiarity and the knowledge that you can’t possibly have experienced this before. It is a very common feeling and almost everybody will have experienced it at least once in their life. For the majority of people it is harmless. However, for some people with epilepsy, a feeling of déjà vu can be a warning sign that a seizure is about to happen.
Déjà vu is obviously not a modern thing, although the phrase is fairly recent. Déjà vu was coined by the French philosopher Emile Boirac in 1876. He was writing a book called “The Psychology of the Future” and he needed a phrase to explain the sensation of having seen something before. There are also phrases for reading something before (déjà lu) and hearing something before (déjà entendu), but we use déjà vu as a catch all term. The scientific name for déjà vu is promnesia, which means “before memory”.
So, what causes déjà vu? It is difficult to know because it is very difficult to test in a lab. It is a sudden sensation, and it is not really possible to make that happen under experimental conditions. There are ways, but they all involve toying with the person’s brain, such as hypnosis, which means the sensation is not completely natural. Because of this, there are a few theories as to why it happens, but no definite answer. The most likely theory is that it is a misfiring in the part of your brain that processes familiarity, which is then fact checked by the part of the brain that processes memory, and found to be false. This means that déjà vu is actually a good thing because it means that the brain is working the way it is supposed to work.
There are two parts of your brain involved when you have a feeling of déjà vu. The first part of the brain is the section that recognizes familiar situations. This is the temporal lobe. It is one of the five lobes of the brain and it is divided into two halves, one on the left and one on the right. They are on the outside of the brain and they stretch from where your temples are to just above your ears. The temporal lobes have many jobs. It is responsible for memory, understanding language, emotions, processing the senses, and visual recognition. Everything you experience in the world around you goes into this part of the brain and is processed. In this part of the brain the senses are constantly compared with the memories so that the right response can be triggered. Our brains work best by knowing what to expect and knowing what reaction is expected to what stimulus. This way, we can avoid danger, which is the brain’s primary concern.
However, sometimes this part of the brain doesn’t get it right. For whatever reason, it analyzes the stimulus that is coming in and decides that it is an experience that we have experienced before. This is nothing unusual. We have experiences we have experienced before thousands of times a day. What makes the feeling of déjà vu is that the temporal lobe sends a signal to the frontal region of the brain, which is in charge of decision making, and the frontal region of the brain says, “Wait a minute. Are you sure we have experienced this before?” The temporal lobe will try harder to find memories, but it is this disconnect between the certainty of the temporal lobe and the uncertainty of the frontal region that creates the uncomfortable feeling of déjà vu. It is a good thing because it means your brain is basically error checking itself. In most cases, the feeling of déjà vu goes away pretty quickly because the temporal lobe realizes that it is actually different. Perhaps it was very similar to an experience we have had, but it is not the same.
There is actually an opposite to déjà vu, called jamais vu. This means “never seen” and it is the feeling that the current experience you are having is the first time, even though you have experienced it before. And this is what I learned today.
Photo by Lisa Fotios: https://www.pexels.com/photo/white-and-green-plastic-toy-1807891/
Sources
https://www.scientificamerican.com/article/what-causes-the-feeling-of-deja-vu
https://pubmed.ncbi.nlm.nih.gov/15217334
https://www.sciencefocus.com/the-human-body/deja-vu
https://www.verywellmind.com/what-is-deja-vu-why-do-we-experience-it-5272526
https://en.wikipedia.org/wiki/Jamais_vu
https://en.wikipedia.org/wiki/D%C3%A9j%C3%A0_vu
https://www.webmd.com/mental-health/what-is-deja-vu
https://www.etymonline.com/search?q=d%C3%A9j%C3%A0+vu
https://my.clevelandclinic.org/health/body/16799-temporal-lobe