5 Questions that still remain unanswered by science #4

Déjà vu

Have you ever had a feeling of having experienced a particular event or visiting someplace before it has actually happened? It is definitely an intriguing, surreal and sometimes a rather unsettling experience.

Déjà vu is derived from a French word. Scientifically speaking, it refers to ‘precognition’ or a feeling of having experienced an ongoing event before.

While it is associated with neurological conditions, epilepsy and psychiatric conditions, as high as 2/3rd of normal people also have experienced this phenomenon at some point in life.

Common findings related to Déjà vu

  1. The déjà vu experience is associated with an aura experienced before an epileptic seizure, especially in the case of temporal lobe epilepsy. The temporal lobes of the brain are associated with processing sensory inputs and may be responsible for this feeling.
  2. It is more common at a younger age and becomes less frequent as we age.
  3. There is not much difference between the genders in terms of occurrence.
  4. Some studies indicate that higher socioeconomic status and a higher degree of travel are related to the higher occurrence of Déjà vu.
  5. Certain drugs also predispose to these experiences.
  6. Stress is one of the triggers too. In a study between two groups – normal and those with known clinical anxiety, it was found to be more prevalent in the ‘anxiety’ group.
  7. It is a common phenomenon in a number of psychiatric conditions such as schizophrenia.

Theories to explain the concept

Some of the theories that attempt to explain this strange phenomenon are as follows.

Dual Processing

These are older theories and have not been proven. But they do lead us to further analysis. The gist of these theories is that two cognitive processes that are supposed to run parallel are de-coupled causing a false sense of familiarity.

  • Familiarity and recall – Recalling ideally happens once familiarity has been established. As per this theory, familiarity erroneously triggers causing a sense of déjà vu
  • Memory encoding and retrieval – When formation and retrieval of memory happen simultaneously it leads to a false sense of re-living a situation. This is not a proven theory either.
  • Perception and memory – If memory formation happens at the same time as the perception of an event it can seem like a past event that is repeating. This is proposed to happen when one is fatigued.
  • Dual consciousness – As per this, two streams of consciousness run in tandem – One, that is projected to the world and the other is one that the mind thinks inwardly. In fatigued conditions, the outward-looking consciousness diminishes and the primitive inward-looking consciousness takes over to cause a feeling of déjà vu


  • Link with epilepsy – The link with aura in the case of Temporal lobe epilepsy is established. In a 2012 study, stimulation of the Entorhinal cortex in the temporal lobe resulted in the feeling of Déjà vu by the subjects. This part of the brain plays a role in spatial memory and memory consolidation. This seems quite plausible as a reason since déjà vu involves falsely remembering unseen places and events.
  • Neural transmission delay – As per this theory, neural information from the eye reaches the higher centres in the brain through multiple paths. In case the information reaches one after the other, the second information is perceived as déjà vu.

Memory-based theory

These focus on how memories are created, stored and retrieved. These theories rely on the concept of ‘familiarity’.

  • A previous similar experience triggering familiarity – This is backed by a 2012 study using VR – Virtual Reality. Participants in the study were shown a set of scenes on VR. A new scene that was not the same but similar to those shown earlier triggered déjà vu in some of the cases.

Hence, a similar place or event stored in our memory can be the source of déjà vu.

  • Familiarity occurring in an unfamiliar surrounding – Our brain processes the familiar inputs faster than those which are not familiar to us. For instance, a person you normally encounter at a bus stop on a daily basis becomes a familiar input. If the same person is spotted elsewhere, the brain processes the familiar person faster than it does the surrounding.

Therefore, as per Whittlesea and Williams’ theory, the faster processing of the familiar but not recognized stimulus results in the entire scene being perceived as familiar to us.

Attention-based theory

As per this theory, if a scene is first seen without full attention and later examined with full attention, it can trigger déjà vu. This happens because the second perception is matched with the first time it was seen inattentively

With advances in research, we are sure to get a better understanding of the concept in time. Meanwhile, déjà vu remains an unsolved mystery and a great source of wonder to all those who experience it.