New Scientist has an excellent article on the neuroscience of deja vu, tackling how our brain can generate the anomalous feeling that we are reliving an event when it has happened for the first time.

The article tackles both experiments that try to trigger and measure deja vu in healthy participants, as well as in people who experience, sometimes permanent, deja vu because of epilepsy of brain injury.

There is one slightly awkward bit in the article however.

One possibility is that d√©j√† vu is based on a memory fragment that comes from something more subtle, such as similarity between the configuration or layout of two scenes. Say you are in the living room of a friend’s new house with the eerie feeling that you have been there before, yet knowing you can’t possibly. It could be just that the arrangement of furniture is similar to what you have seen before, suggests Cleary, so the sense of familiarity feels misplaced… Although the familiarity idea appeals to many, Moulin, for one, is not convinced. His scepticism stems from a study of a person with epilepsy that he conducted with Akira O’Connor, now at Washington University in St Louis, Missouri. This 39-year-old man’s auras of d√©j√† vu were long-lasting enough to conduct experiments during them. The researchers reasoned that if familiarity is at the root of d√©j√† vu, they should be able to stop the experience in its tracks by distracting the man’s attention away from whatever scene he was looking at. However, when he looked away or focused on something different, his d√©j√† vu did not dissipate, and would follow his line of vision and his hearing, suggesting that real familiarity is not the key. The fact that an epilepsy aura can cause d√©j√† vu at all suggests that it is erroneous activity in a particular part of the brain that leads to misplaced feelings of familiarity, suggests Moulin.

This dichotomy is interesting because it implies that ‘brain activity’ and ‘misplaced familiarity’ are somehow separate, when we know each can just be descriptions of the same thing on different levels of interpretation.

However, it also implies that deja vu can only be caused in one particular way, when it could be caused by many different processes.

For example, think about trying to understand why someone got angry. We could be studying one person who gets angry when his football team loose, another when he is wrongly accused and another when he has a seizure in his limbic system.

You could use each one of these explanations to say that the other explanation is wrong if you believed that anger could only be caused in one way.

However, if we accept that it is an experience described at the level of psychology or behaviour there could be many ways of explaining it, and many paths that lead to the same experience, each cause does not cancel the other out.

Like deja vu and probably many other experiences, there are many causes and ways of explaining causes for the same phenomena.

Link to NewSci article ‘D√©j√† vu: Where fact meets fantasy’.