Déjà vu, meaning “already seen” in French, is a commonly experienced phenomenon. Deja vu occurs when an experience we objectively know to be unfamiliar feels instinctively familiar. It is often described as if one is re-living the same moment for a second time or remembering a premonition.
The cause of déjà vu has been widely speculated and scientists offer numerous explanations as to its etiology. However, studying déjà vu in an experimental setting can be problematic since experiences are hard to predict, subjective, and difficult to measure. Therefore, the exact cause remains a mystery but there are some leading theories among experts.
Neurological explanations support the idea that our brain is playing tricks on us. Spontaneous brain activity occurring in the area related to memory may cause a feeling of familiarity. Similarly, another hypothesis suggests a delay in the speed of information transmitted from one area of the brain to another could be responsible for producing incorrect memories of an experience.
Memory explanations suggest that you may have experienced a similar situation in the past but do not consciously remember the experience distinctively from the present moment. Single element familiarity is a hypothesis that déjà vu can be triggered by a single familiar element within an encounter, like seeing your neighbor in a foreign country.
Gestalt familiarity is a more easily tested hypothesis that suggests a familiar arrangement of objects within a scene can provoke a déjà vu experience. For example, walking into a room you have never seen before that has a similar layout to one you are familiar with may cause the feeling of déjà vu.
Whichever hypothesis is correct will require more research to determine; although each hypothesis discussed suggests a momentary glitch in cerebral function resulting in the false feeling of familiarity. For now, scientists need to design more studies to directly measure and examine the causes of déjà vu.