Déjà Vu: Where have I heard this before?
We have all experienced it—the strange and eerie feeling of recognizing something despite encountering it for the first time. This phenomenon known as déjà vu (which in French translates to "already seen") is experienced by 60-70% of adults and can occur upon exposure to a familiar place, person, or circumstance (Obringer). Although the cause of déjà vu was once attributed to the Freudian ego undergoing conflict, recent studies propose that the cause of déjà vu can be attributed to the brain's recognition memory. Memories stored as individual elements or fragments switch back and forth between familiarity and recollection memory. When an event is stored as a recollection memory, a person would be able to recall that experience when encountering a new but similar event. However, in the case of déjà vu, when a past event is stored as familiarity memory, a different yet similar event would trigger the illusion of familiarity instead of an exact recollection ("The Psychology of Déjà Vu").
Neuroscientists at the Picower Institute for Learning and Memory at MIT may have shed light on the neurological mechanisms that create the sensation of déjà vu. Their research focuses on the hippocampus (see Figure 1), the structure of the brain that is involved in storing memories. The researchers demonstrated that in mice one gene in the dentate gyrus (shown in Figure 2) – one region of the hippocampus – is involved in differentiating between old and new memories, a process known as pattern separation. Mice who expressed this gene were able to distinguish between two similar chambers, while mice who lacked this gene believed that similar chambers were the same. These findings indicate that the dentate gyrus may play a role in the storage of memories as familiarity and recollection memories (McHugh et al). Hippocampal neurons known as place cells may contribute to the sensation of déjà vu. When a person views a new location, the place cells fire electrochemical signals, allowing the spatial arrangement of the setting to be recorded. When this person views a similar location, different but overlapping neurons fire. If there is a sufficient amount of overlap between the two sets of neurons, the person will feel the uncanny feeling of déjà vu (Halber).
Other hypotheses exist that explain possible biological mechanisms that cause people to experience déjà vu. Psychologists, neuroscientists, and other researchers continue to study the various processes that interplay to create this ubiquitious and uncanny phenomenon.