there is a phenomenon called 'recollective confabulation', where people, often with dementia, try to make sense of new situations by fitting them into a story. It is suggested that, ironically, familiar situations don't seem to cause this deja vu, only the stress of dealing with a new situation or new people. This is not actual deja vu (see below), it is just a strategy for dealing with the unfamiliar, as is all confabulation, just the mind tidying things up and making it possible to cope by creating a story out of past memories mixed with new sensory input.Deja vu (in the sense of misperceived memories) is a perceptual trick that the mind plays to create a 'memory' out of dreams or current experiences. Deja vu is not confined to people with brain damage, it can happen to anyone, but it does seem to happen more often in older brains. It is also frequently experienced by epileptics.
I'm not sure I understand how this happens but I think that it's when we experience an event and our mind has some sort of wobble when storing this in short-term memory, so that we get the message that we have retrieved the event from long-term memory.
MIL experiences deja vu a lot and we think for her it is a processing problem due to the brain damage that causes her vascular dementia. There seems to be a time lag between seeing something and making sense of what you've seen, and in that time gap the brain has registered once subconsciously and then registers the event again consciously, so it seems like it has happened twice.
A recent Horizon programme about the subconscious mind indicated that the conscious mind is only a tiny fraction of our 'mind', with the subconscious doing most of the work There are links from what our eyes 'see' both to the visual processing centres and also to those older parts of the brain that register movements in the objects around us so we can react quickly to danger. We don't just 'see', we experience the effects of visual stimuli in different parts of our brain and for different reasons. All of which waffle means that when we think we have deja vu, in a sense we always do, it's just that if our brains work 'normally' we are not usually aware of this.
