What causes déjà vu?
One side of your brain is usually 'in charge' of a particular skill – for example, in most people, the left side of the brain deals with language. One explanation for déjà vu is that there is a split-second delay in transferring information from one side of the brain to the other. One side of the brain would then get the information twice – once directly, and once from the 'in charge' side. So the person would sense that the event had happened before.