Have you ever experienced this feeling that this scenario or situation is very familiar, or you have seen it before? You feel kind of familiarity in situations.
This strange phenomenon is called déjà vu. It’s very normal and occurs in 60 – 80 % of population, the age group facing frequently is 15 – 25 years old. It lasts for only 20 seconds. As it occurs so rapidly and suddenly, this makes it very difficult to study. Some scientists call it sophistry or delusion of some sort.
Some scientists are of the view that it happens due to incongruity in the brain when it is trying to understand something with little as input. Neurologists also believe that memory recollection output and current brain input both are mixed up, when déjà vu episode occurs. However this believes is considered vague as it does not explain why déjà vu is not related to past experience.
There is another theory that during storage of an experience, there is some kind “leak out”, of information. In our memory storage pathway, at first experiences are stored in short term memory and the too long term memory. This theory postulates that there is a glitch or slip between short and long term memory. The information accidently settles in long term memory instead of short term memory, skipping the usual storage system. So that’s why during the déjà vu episode we feel a memory from distant past, in response to a current experience in our short term memory.
We are conscious when déjà vu occurs that suggests that entire brain participation is not necessary especially in non epileptic individuals.
Researchers have experimented on epileptic patients by using intracerebral electrodes. They have found out that culprit is medial temporal lobe. It is responsible for retention of long term memory. It is where the epileptic seizures begin. The seizures start by changes in neuron activity in focused area of brain. This defected neuronal activity spread like earth quake in all the brain including medial temporal lobe. Prior to epileptic event this malfunctioned activation produces déjà vu.
The areas of brain from where these signals begin could be identified by measuring the amount of neural discharge in epileptic patients. Déjà vu is more easily induced by electrical stimulation of rhinal cortices compared to hippocampus. Entorhinal and perirhinal cortices are stimulated thus can induce déjà vu. These structures are involved in processing of episodic sensory and memory. This suggests that déjà vu is induced by debilitated electrical discharge.
In people without epilepsy these electrical discharges occur in non pathological manner. Researchers are of the view that similarly déjà vu could be triggered in non epileptic patients by the electrical discharge. Some researchers believe that typical normal déjà vu is different from epileptic episode of déjà vu.
There is another theory that rhinal neural system activation is responsible for the sense of familiarity. Clinical neurophysiology published a study that tells about interaction of amygdala, hippocampus, and rhinal cortices to produce déjà vu in epileptic patients. Rhinal cortex is responsible for detection of familiarity and hippocampus is linked to detailed recollection. French researchers say that neural interaction increased between rhinal cortices and amygdala or hippocampus upon stimulation. From this we can deduce that some coincident occurrence in medial temporal lobe triggers activation of recollection system.
So far the cause and mechanism of déjà vu is still not clear. But as it’s normal and there are many techniques with which we can understand it. Until then don’t panic or go nuts because it’s safe and normal. So enjoy this strange sensation that captures you or pretend to be a fortune teller.