For many of us, the déjà vu sensation is a very curious and rare phenomenon, but there are some people who experience it on a daily basis, the feeling becoming chronic.

Up to now, psychologists have been unable to study it properly, mainly because it all happens in the blink of an eye, during which the subject feels as if he has just replayed o certain sequence of his/her life.

The chronic condition of the déjà vu feeling was first seen in a memory clinic by Dr. Chris Moulin.

"We had a peculiar referral from a man who said there was no point visiting the clinic because he'd already been there, although this would have been impossible", the psychologist said.

The patient actually believed that he had already met Dr Moulin, but he also gave specific details about the times and places of those 'memories'.

Déjà vu has developed to such an extent that he had stopped watching TV, even the news, because it seemed to be a repeat. Chronic déjà vu sufferers are not only overwhelmed by a sense of familiarity for new experiences, they can provide plausible and complex justifications to support this.

"The exciting thing about these people is that they can 'recall' specific details about an event or meeting that never actually occurred. It suggests that the sensations associated with remembering are separate to the contents of memory, that there are two different systems in the brain at work."

Dr. Moulin believes a circuit in our temporal lobe fires up when we recall the past, creating the experience of remembering. In a person with chronic déjà vu this circuit is either overactive or permanently switched on, creating memories where none exist.