Most people experience deja vu sometime in their lives-the feeling of having already experienced something when it's actually being experienced for the first time. Dutch psychiatrist Herman Sno believes deja vu can be explained by better understanding the nature of memories. His theory is that memories are stored in our brains in something similar to a hologram format, with each section of the hologram containing enough information to recreate the entire picture. Deja vu occurs when a detail of one's current experience closely matches a memory fragment, resulting in a hazy recreation of an earlier memory. For Sno, deja vu can also be explained in terms of matching models.
An experience may seem familial because it is somewhat similar to a large number of events stored in our memories. For example, if you were shown pictures of the members of a family who have a strong resemblance to one another, and then you happened to see another family member on the street who wasn't in the picture, you might think the person looked familiar, even though you might not associate that person directly with the pictured family.
Cognitive psychologists and neuroscientists have approached deja vu from a different angle. They distinguish two memory types: those we consciously recollect and those memories based on familiarity, in which we cannot directly recollect the person or situation. Most of us consciously recollect important events in our lives, but we sometimes meet people or experience situations we only vaguely recognize- familiarity without conscious recollection. Researchers believe that, normally, conscious recollection stimulates the prefrontal cortex, a part of the brain believed to be used for storing familiarity. According to this theory, dejin vu occurs when both the prefrontal cortex and the area storing familiar memories are stimulated, but a conscious recollection is missing.