Déjà Vu: Its Meaning and Why We Experience It

Déjà vu is literally translated from French to mean “already seen.” It is a sense of having already seen something—coupled with knowing you haven’t actually seen it, which is why it catches many people so off guard. It is thought to be the equivalent of a small brain “glitch,” with two streams of thought colliding.

It is an incredibly common experience, something upwards of 97% of people are thought to have experienced it at least once, with more than two-thirds of people experiencing it with some regularity.

St. Augustine, an ancient philosopher, first referred to the concept of déjà vu in 400 AD as “false memoriae,” but French philosopher Emile Boirac was the first to use the term déjà vu in 1890. The first use of the phrase in the scientific world was from F.L. Arnaud, a neurologist who proposed to use it at a meeting of the Societe Medico-Psychologique.

Early research showed promise for déjà vu to be a sign that helped doctors diagnose epilepsy, but more recent research has shown it may be a matter of perception or memory.

How Does Déjà Vu Happen?

It is believed that déjà vu may be the result of two different streams of awareness colliding: the experience of recognizing a current situation, alongside the feeling that this is an inaccurate recollection. A key feature is that the person realizes that they have not actually seen this before.

Sometimes, what happens is really a matter of split perception and someone is processing a sight twice because they may have been distracted or their vision was obstructed for some reason. 

The second perception, immediately after the first one, becomes the one that is consciously experienced—but it feels unfamiliar because we are not cognizant of the first experience, which we only partially processed. 

Types Of Déjà Vu

Though the actual feeling of déjà vu is the same across people with healthy brains and those with neurological conditions, different things are happening in the brain during each of these types.

Those who do experience it more regularly show less grey matter than those who don’t.Grey matter is the outermost layer of the brain, and it is responsible for controlling movement, memory and emotions. Typically, the more grey matter a brain has, the more effective it is.

In those with neurological conditions, three parts of the brain are impacted: the hippocampus, parahippocampal gyrus, and temporal neocortex—areas that are associated with forming and retaining memories.

For those with epilepsy and déjà vu, alterations in memory circuitry have been observed, meanwhile, alterations in emotional circuitry are seen in “healthy” individuals experiencing déjà vu. Déjà vu is thought to perhaps be abnormal signaling within the medial temporal lobe, which governs memory processing, particularly visual memories.

The conditions that might experience more déjà vu than those with a healthy brain include:

• Schizophrenia
• Epilepsy
• Anxiety
• Vascular dementia

The term déjà vu is the one most frequently used to capture these types of experiences, but there are actually many more of these phenomena.

Some other types you might experience:

• Déjà entendu: already heard
• Déjà éprouvé: already experienced 
• Déjà fait: already done
• Déjà pensé: already thought
• Déjà raconté: already recounted
• Déjà senti: already felt emotionally or already smelled
• Déjà su: already known (the knowledge of)
• Déjà trouvé: already found
• Déjà vécu: already lived through
• Déjà voulu: already wanted

What Causes the Déjà Vu Feeling?

Though most times, déjà vu is not a sign of anything serious—such as a mental illness—there are some possible factors that you might want to pay attention to if episodes of déjà vu are making you uncomfortable.

People who are tired and/or stressed often report episodes of déjà vu. This is thought to be because fatigue and stress typically affect both long- and short-term memory. 

A hypothesis is that excess amounts of dopamine may be implicated in experiences of déjà vu. In studies of temporal lobe epilepsy, the research shows that elevated levels of dopamine were detected in rodent models of temporal lobe epilepsy.

One strange cause of déjà vu is the use of the flu medications amantadine and Proin (phenylpropanolmine). A case study writes about a man who took this combination of medications to treat an infection of the flu and began experiencing several episodes of déjà vu per hour—which stopped upon him stopping these medications.

Both of these medications, among their flu-symptom reducing properties, work on the dopamine system, and it is thought that these déjà vu episodes were caused by an excess of dopamine in the system. Epilepsy research shows that parts of the brain including the hippocampus are related to dysmensic symptoms (impaired memory) symptoms,

Who Gets Déjà Vu?

While anyone can experience déjà vu, those who experience it multiple times share some characteristics, according to research:

• High income
• Well educated
• Frequent travelers
• Those who remember their dreams
• Those who are politically liberal 
• Ages 15-25

Should I See a Doctor for Déjà Vu?

Epilepsy is the most common of neurological conditions to be associated with déjà vu, as it affects the temporal lobe of your brain, where vision is interpreted. There are several types of seizures, but it is simple partial seizures, also known as focal onset aware seizures, that are most often associated with deja vu experiences.

For most healthy individuals, déjà vu has no serious impact, other than a bit of a feeling of confusion momentarily. However, if you are experiencing frequent déjà vu (a few times a week or more), you may want to visit a neurologist to be evaluated for epilepsy or any other neurological conditions.