Most of us, at some point in our lives, have been in a situation that felt surreally familiar. It may have even felt as though we were reliving a past experience. This feeling is commonly referred to as déjà vu, which is the French term for "already seen." Although déjà vu tends to be dismissed soon after the feeling passes, scientists now have a better understanding of its origins and have developed many theories to explain why it occurs.
In order to fully understand déjà vu, it is first necessary to identify its origins. For many years, scientists have known that the hippocampus is a region in the brain that converts short-term memories into long-term memories. However the role of the dentate gyrus, a small portion of the hippocampus, was only recently understood. After conducting a study on rodents, neuroscientist Susumu Tonegawa discovered that without a properly functioning dentate gyrus, rodents could not differentiate between two very similar situations (1). As Tonegawa explains, this is the problem with memory that occurs when we experience déjà vu (1). When certain aspects of memories from a past situation overlap with the stimulation our brain is receiving from a current situation, the body refers back to the dentate gyrus to distinguish between the two (1). However, when cells in the dentate gyrus become damaged or decrease due to age or brain diseases, the present gets blurred with previous memories, and the feeling of déjà vu results (1).
However, as psychologist Dr. Alan Brown points out, the elderly and brain disease patients are not the only ones who experience déjà vu (2). Normal, healthy individuals can also feel the strange sensation when small malfunctions occur in the brain's processing of short-term and long-term memories (2). For example, when the brain absorbs information about a current experience, short-term memories begin to form (3). However, if the brain experiences even a minor glitch during this time, it causes us to incorrectly identify short-term memories as long-term memories, resulting in déjà vu (3). This confusion can also arise if the brain experiences a slight interruption while storing current information into our memory (3). When this occurs, it causes us to feel as though we are experiencing and recalling a situation simultaneously (3).
Although there are many theories about déjà vu, scientific evidence has dispelled much of the mystery that surrounds this vaguely familiar sensation. As a result, we have gained a better understanding of how our bodies function. Through studies of déjà vu, scientists also learned that exhaustion, stress, and certain illnesses contribute to its prevalence (2). Therefore, the next time we experience déjà vu, instead of brushing it off, perhaps we should look at it as our bodies' way of telling us that we need to get more rest, minimize stress, pay more attention to our health, and improve the overall quality of our lives.