Once in a completely new place, have you ever felt that you are familiar with everything here, and have you been here before? Or the feeling that you've had the same conversation with someone before?
This feeling of "recognition" is known as "déjà vu" (a French word meaning "already seen") and is reported to be familiar to 60-80% of people. This event is always fleeting and arbitrary.
Which area of thought is responsible for these feelings of recognition?
Despite widespread coverage in popular culture, the phenomenon of déjà vu remains unexplored in scientific circles. Deja vu happens quickly, without warning, and has no other physical manifestation other than the message: "I just had a deja vu!"
Many researchers speculate that this phenomenon is a memory-based experience and that the brain's memory centers are responsible for it.
Memory systems
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The middle temporal lobe is responsible for maintaining long-term memories of events and facts. Certain areas of the middle temporal lobe are important in the emergence of knowledge or recognition, as opposed to the detailed memory of certain events.
Recognition is assumed to be dependent on olfactory function, whereas detailed memory is related to the hippocampus.
The arbitrariness of the events of déjà vu in healthy people makes it difficult to study in an empirical manner. Any such research is based on the self-perception of the people under study.
False signal in the matrix
Many people with epilepsy consistently experience déjà vu at the onset of a seizure, when the seizure begins in the middle temporal lobe. This gave researchers the opportunity to experimentally study déjà vu.
Epileptic seizures are caused by changes in electrical activity in neurons in the central regions of the brain. This dysfunctional neural activity can spread throughout the brain like a shockwave from an earthquake. The regions of the brain in which this electrical activation can occur include the middle temporal lobes.
The electrical disturbance of this nervous system creates an aura (a kind of warning) from the deja vu before the seizure. By measuring the release of neurons in the brains of these patients, the scientists identified the areas of the brain where the déja vu signals begin.
It has been found that deja vu is more likely to be induced in epileptic patients by electrical stimulation of the olfactory cortex as opposed to the hippocampus. This suggested that déja vu was caused by a dysfunctional electrical discharge in the brain.
These neuronal secretions can occur in a non-pathological manner in people without epilepsy. An example of this is the involuntary convulsion that can occur when you fall asleep.
It has been suggested that déjà vu might be triggered by such neurological unloading, leading to a strange state of recognition. Some researchers have argued that the type of déjà vu experienced by patients with temporal lobe epilepsy is different from the typical déjà vu.
A déjà vu experienced before an epileptic seizure may be persistent, rather than a fleeting feeling, as in people who do not have epileptic seizures. In people without epilepsy, clear recognition is combined with the knowledge that the environment is truly new, essentially reinforcing the déjà vu experience.
Inconsistencies and short circuits
Deja vu in healthy people is considered a memory error that can jeopardize the nature of the memory system. Some researchers believe that déjà vu is due to a deviation in memory systems leading to the inappropriate generation of detailed memory from new sensory perception.
Thus, information bypasses short-term memory and instead reaches long-term memory.
This means that déjà vu is caused by a mismatch between sensory input and memory recall. This explains why new experiences may seem familiar, but not as real as a fully resurrected memory.
Other theories suggest that the activation of the olfactory nervous system involved in the recognition process occurs without activation of the memory system within the hippocampus. This leads to a sense of recognition without specific details.
In connection with this theory, it has been suggested that déjà vu was a reaction of the brain's memory systems to familiar experiences. This experience is known to be new, but has many recognizable elements, albeit in a slightly different setting. Example? You are in a bar or restaurant abroad that has the same layout as the bar you go to regularly at home.
More theories exist regarding the cause of déja vu. They range from the supernatural - past lives, alien abduction, and unconscious daydreaming - to memories formed from events that are not immediate (such as scenes in films).
Until now, there is no simple explanation for why déjà vu occurs, but advances in neuroimaging techniques can help our understanding of memory and the tricks that our consciousness throws out with us.
