Do you have the impression that you have already encountered any new situation? Although most people have experienced this feeling of “deja vu”, its scientific explanation is not yet very clear.
The feeling of deja vu is more often observed in young people, in situations of overwork or stress. There are many theories explaining this, some relate to paranormal phenomena: memories of a past life, premonitions… Scientists have also tried to solve this mystery in order to find more rational explanations.
Feeling of deja vu in people with epilepsy
Deja vu has been studied, in particular, in people suffering from epilepsy, because it is a common symptom during seizures. During an epileptic seizure, the electrical activity of some neurons changes. This dysfunction spreads through the brain, and electrical activation affects the middle temporal lobes. This electrical disturbance causes a sense of deja vu at the beginning of the crisis.
The area responsible for this sensation in epileptics is the area of the nose located under the hippocampus. So, in a study published in 2012, French researchers managed to stimulate a sense of deja vu in epilepsy patients by stimulating the cerebral cortex. But what about people who don’t have epilepsy? Either comparable electric shocks occur in the temporal lobe in the absence of epilepsy, or deja vu occurs due to other processes.
The role of the frontal areas of the brain
In 2016, researchers from the University of St. Andrews (UK) spoke about the results of scanning people experiencing deja vu at a conference dedicated to memory. To evoke this feeling, the researchers presented them with a list of words that had a connection (pillow, bed, night, sleep…) without a keyword connecting all these words (sleep). The researchers asked the participants if they had heard words beginning with the letter “c”, and they answered “no”. When later they were asked if they had heard the word “dream”, they remembered that they had not heard it, but at the same time this word was familiar to them: they had a feeling of deja vu.
The team performed MRI scans of the brains of 21 volunteers and showed that memory-related areas, such as the hippocampus, were not involved in this phenomenon. On the contrary, the frontal regions of the brain, which play a role in decision-making, were activated. One hypothesis is that the frontal regions of the cerebral cortex test memory and send error signals when there is a conflict between what we have experienced and what we believe we have already experienced. A sense of deja vu would be a sign that the memory check system is working well.