Reading this article, perhaps clicking on the link to this web page, did you feel somehow like you've already been here before, already read this page? Do the images on the page seem familiar, even though you're just certain you've never visited the Curiosity Web site before? If you're feeling those things, you're experiencing déjà vu, something we all feel from time to time. As to why it happens, the world of science isn't entirely sure, but to find an answer they're looking where they often look: the brain.
But before we look to the brain and its various firings, let's look to other possible explanations. Renowned psychoanalysts Sigmund Freud and Carl Jung thought, respectively, that déjà vu stemmed from repressed memories or the mind digging deep into the human collective unconscious. Some even thought déjà vu, which comes from the French for "already seen," was the result of a kind of time lag between the hemispheres of the brain such that by the time visual input processed in one hemisphere went to the next, the latter brain area experienced it as a memory. They called that a visual disconnect [source: Stanton].
Now, looking to the brain's wiring for a cause for déjà vu, we come to the hippocampus region, which has the job of creating new memories and also handling our sense of direction. In 2007, a biologist at the Massachusetts Institute of Technology discovered receptors in the hippocampus that have the task of distinguishing between similar-looking but different places. It's thought that perhaps the brain could be experiencing a short-lived lapse in the receptors' normal function when déjà vu occurs [source: Popular Science].
Déjà vu was also at the heart of a 2009 study that looked at how the memory handles objects and the configuration of objects. It turns out we excel at remembering familiar objects when we see them in unfamiliar places, but things get a bit muddled for us if we're trying to dig up a memory based just on the configuration of objects. What that means is that the powerful feeling of familiarity we get sometimes in unfamiliar surroundings (déjà vu) could be related to how the objects are configured. For example, if you stand in the living room of a home you've never visited, but the layout of the furniture is exactly like your own living room setup, your memory will cook up a sense of having been there before -- you'll get that strong feeling of "knowing" you've been there before [source: Markman].
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