You take a step, and are thrust into a fragment of memory you can’t quite remember. The world seems to spin in an uncannily familiar way, and you’re sure this has happened before. The people are exactly where you recall them to be—their conversations exactly as you would predict. Then, just as quickly as the feeling comes, it vanishes in a fleeting moment despite your attempts to grasp it.
Around 60-70% of the population experiences the spontaneous sensation of déjà vu, meaning “already seen” in French, during their lifetime [1]. It has been observed to be most prevalent in ages of 15-25, with the feeling becoming less common with aging. Ultimately, déjà vu is caused by miscommunication between the different parts of the brain, specifically the temporal lobe and hippocampus: the brain structure responsible for processing new information. This miscommunication, which can result from certain triggers or interactions with the environment, can render one unable to identify the border between a memory and new experience [2].
Because of déjà vu’s unique characteristic of vanishing almost spontaneously, it is still a relatively undiscovered area of cognitive science and a mystery to the neurology community[4]. However, some suggest that certain individuals, such as those who have higher levels of education, are frequent travelers, regularly remember dreams, or undergo higher amounts of stress and tiredness, may be more susceptible to déjà vu [1,2].
Researchers have speculated multiple theories that may contribute to déjà vu, one being “dual processing” or “split perception theory” [1, 5]. This theory describes the confusion the brain faces when absorbing information, and categorizing it as old or new knowledge. An individual may receive a quick stimulus when they are distracted or in a state of unclear mind, resulting in an incorrect or weak perception of reality. Upon receiving that stimulus again, the mind may recognize it as familiar, but not fully recall or register experiencing it before [5].
On the other hand, the “Glitch Theory” suggests that déjà vu is a result of neurons sending unintentional electrical impulses throughout the body after witnessing a certain stimulus. Researchers have even compared this to the involuntary jerks which occur when someone is sleeping, known as hypnagogic jerks. Both are similar in relation to neurons creating signals that do not align with what the body is truly experiencing [5]. Another common hypothesis for déjà vu is the “Electrical Malfunction Theory”. It suggests that brain signals called synapses are slightly mistimed and mismatched, occasionally causing brief confusion in what is being seen [5]. This can lead to the sensation known as déjà vu. Lastly, some experts theorize that the brain has two consciences, with one focusing on the activities going on in the world outside, and another prioritizing inner mental processes. Thus, when one is tired or deprived of proper rest, the brain may confuse these two consciousnesses, leading to déjà vu [1].
To test the connection between memory and déjà vu, researchers developed virtual reality scenes and played them before a group of individuals. When those individuals were later brought to areas with similar surroundings, many noted having a vague sense of déjà vu. The results of this test support the idea that environmental triggers contribute to déjà vu.
It’s important to note that the occasional occurrence of déjà vu is not a matter of concern, but in rare circumstances, it can be a sign of neurological disorders. While déjà vu has been noted to persistently happen to those with dementia [2, 4], individuals who suffer epilepsy or have temporal lobe seizures may also experience it more frequently [1]. This is due to the fact that people with temporal lobe seizures often experience déjà vu before the seizures start. Since seizures result from excessive bursts of abnormal electrical energy, some researchers believe déjà vu might merely be a small, electrical mistake in the body [3]. It’s also been proposed that recurrent anxiety can lead to déjà vu, as both take place in the hippocampal formation, although further evidence is needed to support this theory. Ultimately, although déjà vu is safe in most cases, when it is accompanied by confusion, headaches, weakness, shaking, or loss of awareness, it is wise to seek medical attention [2].
The abundance of theories regarding déjà vu shows how much is yet to be discovered about the human brain. So, the next time that strange haze of familiarity washes over you, stop and wonder about that little mystery in your great, complex, brain.