‘You don’t believe in energies’, she sneered at me disdainfully,’they exist you know.’

‘The human soul is timeless and hence knows everything,’ she said. ‘Then why do we have to study for exams?’ my son asked her as I tried to avoid the harsh look she gave me for being a bad parent.

‘You say you believe in the brain and always look for evidence, so tell me Mr Scientist, how do you explain deja vu?’

Introduction

Everyone I have met and have had the opportunity to talk about it, has experienced ‘deja vu’. Imagine you walk into room in a house you have never been in and suddenly the strangest of feelings washes over you: ‘OMG, I have experienced this exact moment before.’ The familiarity is overwhelming, when it shouldn’t be familiar at all. The sensation becomes stronger and stronger and then completely leaves just like water in a sink once the stopper is opened, all within a matter of seconds.

It’s nearly the same feeling that my niece had when she took responsibility of earthquakes as soon as she landed, ‘ I am God’, she said as she felt the surge of endorphins pulsating through her body. As soon as you get the feeling of deja vu, you are stuck with the thought, did I predict the future that I just landed in? But then when you dwell upon that thought, chances are that you will not be able to pinpoint exactly when you had experienced that premonition before.

Like most mysterious things, ‘deja vu’ is a term in French that literally translates to ‘already seen’. Statistically it is reported to occur in 60-70% of people, most commonly between the ages of 15 and 25. Since ‘deja vu’ occurs randomly and in individuals without a medical condition, it is extremely difficult to study in laboratory conditions. Throughout the period that we have been alive to this phenomenon, it has been up to a lot of speculation. Psychoanalysts have attributed it to wishful thinking, Psychiatrists cite mismatching in the brain causing us to mistake the present for the past. Parapsychologists and Healers even believe it is related to a past-life experience. I have also been told by a wise man that when we sleep the soul roams around and since it does not fall within the limits of time and space, it goes into the future and brings snapshots which when we land in, leads to the feeling that we have seen this earlier – or this has happened to me earlier.

Research

There are three schools of thought regarding ‘deja vu’.

One is that déjà vu occurs when there is a mismatch in the brain during its constant attempt to create whole perceptions of our world with very limited input. To elucidate this, think about how associative memory works. It starts with small bits of sensory information (a familiar smell, for instance) and leads to a place, a time, people, conversations and even feelings associated with the event in question. ‘Deja vu’ is suggested to be some sort of “mix-up” between sensory input and memory-recalling output.
The second theory states that ‘deja vu’ is a fleeting malfunctioning between the long-term and short-term memory circuits in the brain. Researchers postulate that the information we take in from our surroundings may ‘leak out’ and incorrectly shortcut its way from short-term to long-term memory, bypassing the normal storage transfer mechanisms. When a new moment is experienced—which is currently in our short term memory (located in the hippocampus) it appears as though we’re drawing upon some memory from our distant past (the temporal lobe). This temporal entanglement causes the brain to incorrectly attribute a present memory to a past memory.
The third hypothesis suggests that ‘deja vu’ is an error in timing (again what I call a temporal entanglement). While we perceive a moment, sensory information may simultaneously be re-routing its way to long-term storage, causing a delay and, perhaps, the unsettling feeling that we’ve experienced the moment before.
There is however, one characteristic that is common to all ‘deja vu’ experiences – irrespective of age, race and sex – we are completely conscious that they are occurring, implying that cognitive awareness is active and therefore it implies that it is not a cognitive failure.

Studies of epileptic patients investigated with the use of intra cerebral electrodes have demonstrated that stimulation of the rhinal cortex can actually induce a déjà vu episode. Parts of the rhinal cortex, such as the entorhinal and perirhinal cortices are structures involved in episodic memory and sensory processing.

A study analyzed the patterns of electroencephalography (EEG) signals from the rhinal cortices, hippocampus (involved in memory formation), and amygdala (involved in emotion) in epileptic patients for whom deja vu had been induced by electrical stimulation. The researchers found that synchronized firing of neurons between the rhinal cortices and the hippocampus or amygdala were increased in stimulations that induced the phenomenon of ‘deja vu’.

So what exactly happens

If we focus on the visual system of human beings, sensory information travels through the lens, falls on the retina where the light excites rod/cone cells which in turn convert the light into an electrochemical impulse fed up the optic nerve. The input, from one optic nerve of each eye, goes through the thalamus to the somatosensory cortex. Now during this travel of the electrochemical signal, there is a mismatch between the fast electrical impulses which jump over the glial cells, and the chemical impulses which jump across synapses of nerve cells. The cortex is the area that plays a key role in memory, attention, perception, awareness, thought, language and consciousness. Now when all information reaches those centers at or around the same time, there is no problem and as Aamir Khan said in the movie 3 Idiots – ‘All is well.’

However, when there is a mismatch in timing, there is a difference in processing along neural pathways. This causes the perception to be disrupted and is thus experienced as two separate messages. The first version is interpreted as what we call first access. This is what we see as soon as we open our eyes or walk into a room or pull open the curtains. The brain interprets the second version, through the slowed secondary pathway—as a separate perceptual experience. As there is no change in the environment, two different images are ‘made sense of’ or ‘perceived’ by the brain as of different temporal sequences – meaning one image we are seeing now, while the other we ‘must have seen earlier.’ And this must have seen earlier image is what the French annotated as ‘already seen’ – ‘deja vu.’

So the next time it happens to you – don’t reach for your mobile phone to call your fairy godmother. And my apologies for deromanticising something that you had been conveniently attributing to a higher power, or higher faculties or higher whatever.

Sorry young man/lady, you’re not God. It’s the neurons!

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