Imagine you are taking a tour of your friend’s new house. As you walk up the stairs to their room, you have the eerie feeling that you know what is going to happen, accompanied with the sudden sensation that you have already lived this moment. Even though you subconsciously know this is impossible, you cannot help but feel the nagging sense of déjà vu.

Déjà vu, meaning “already seen” in French, is a psychological phenomenon where one feels impossibly familiar with a new experience. Psychologist Alan Brown estimates that about ⅔ of the human population experiences déjà vu, marking it as a common “glitch” in human memory. 

Until the late 1990s and early 2000s, most modern research relating to déjà vu was connected to paranormal or supernatural experiences. In fact, Colorado State University describes many theories on the phenomenon as being influenced by the belief in reincarnation or former lives. Thus, the majority of déjà vu studies only began in the early 2000s, when Alan Brown began to view the sensation from a psychological perspective. 

Through his research, Brown found that the most common trigger of déjà vu is a “scene” or the way in which objects are arranged in a room. This was supported by the 1930s hypothesis called the “Gestalt familiarity theory,” which essentially described that if an area has a similar layout to a new, separate area, then the new area will trigger déjà vu (despite the differing circumstances). 

In terms of neuroscience, the National Library of Medicine states that the main culprit of déjà vu is the medial temporal lobe. Found behind your temple, the section is a crucial component in reflection. When this lobe fires, it causes your brain to retrieve a memory to relate to what you are currently experiencing. However, this lobe can fire accidentally as well, forming the déjà vu phenomenon. In fact, younger people tend to experience déjà vu more than adults because of the underdeveloped medial temporal lobe being overenthusiastic and firing unnecessarily. 

 However, déjà vu also occurs because of the “fact-checker” that is found in the frontal cortex of the brain. When the medial temporal lobe fires accidentally, the frontal lobe fact-checks the memories correlating with your current situation. When it realizes the relation between the memories is incorrect, it causes confusion within your brain. A report from the Scientific American clarifies that déjà vu occurs because your frontal lobe realizes your memory has been mistaken, creating the uncomfortable feeling that we identify with the phenomenon. 

When the brain consistently fails to recognize its error using the frontal lobe, déjà vu can turn into dementia. The earlier Scientific American report mentioned also explains that when someone with dementia experiences something new and their medial temporal lobe fires, their frontal lobe is unable to recognize the error and truly believes that the situation has happened before. This is primarily why those suffering with dementia make up experiences that have never truly happened to them. 

Cognitive psychologist Anne M. Cleary also explains that people may find that déjà vu is similar to knowing a word but being unable to think of it in the moment. This phenomenon is known as the “tip-of-the-tongue” phenomenon, and it may feel akin to déjà vu because it utilizes the same parts of the brain. Cleary explains in the academic reference “Learning and Memory: A Comprehensive Reference (Second Edition), 2017” that you are using your frontal lobe to understand that you know the concept of the word in question. While this is happening, you are also attempting to retrieve the word from your medial temporal lobe, thus using the same functions that you would when experiencing déjà vu.  

However, Cleary also mentions that replicating and researching déjà vu in a lab is a difficult task. Thus, current research is still ongoing, and many institutions (such as the Colorado State University and the University of Saint Andrews) continue to provide insight on the phenomenon. Nonetheless, the next time you feel déjà vu, know that it is not a supernatural occurrence and that it is rather a normal glitch in brain function.