Déjà vu - the decay of a Lego house memory?

Edward Johnson

Tue, 20/04/2010

“How can the same shit happen to the same guy twice?”; muttered from the foul mouthed, generally bad-ass cop John McClane in Die Hard 2 as he yet again finds himself crawling around ventilation shafts in order to foil a terrorist plot. In this case our chain-smoking New Yorker was merely venting his anger, but this quote does ask a pertinent and deceptive question – how is it that we believe we are experiencing something that we think we have experienced before? Why do we get déjà vu?

I’m sure a lot of you have experienced this phenomenon before. I know that I occasionally get flashes of déjà vu, and I’m sure you’ll agree that it is…weird. Defining déjà vu is surprisingly difficult considering it is something that a lot of us experience. It can be briefly defined as “self assurance that you have witnessed or experienced a new situation”. The “new situation” part causes some confusion – as the situation can be entirely new (such as recognising a hotel you have never seen before in a country you have never been to), or new in a more precise sense (such as noticing someone you vaguely recognise walk past you in a new shirt). It is this ambiguity in the meaning of “new” that offers a slight hint as to what the hell is going on.

Perhaps the best way to explain this phenomenon is with an example. You may be walking home at night, with a song from your iPod as you pass your local Chinese take away. A red Vauxhall Astra passes you and then turns into a quiet street. It’s then that you have a slightly unsettling feeling of intense familiarity; it’s almost as if you have been in this exact same situation before. You then feel incredibly compelled to figure out where and when you were in this situation, but you can’t. Try as you might, you’re not able to pinpoint exactly at what point in your history that you witnessed this precise series of events. It’s even a little frustrating. The actual truth is, you never have experienced this exact series of events – but you have previously been in a situation very similar to this. I know that this isn’t the first time that a red Vauxhall Astra has passed me in the street, but there is no physical way that this exact situation at this point of time is exactly the same as a situation like it that occurred in the past. Variances as noticeable as a gentle breeze, or as subtle as the precise arrangement of all the molecules in our body occur between any two situations. Perhaps the idea of entropy can help explain this phenomenon at a molecular level – the order of all the atoms in an object may never be truly the same in two situations.

Of course, we cannot perceive such exceedingly minute changes in the environment. In fact the human brain is very easily fooled, and it often makes things up. Our vision is a classic example of our noggins playing tricks on us. The human visual field has a blind spot which can be deduced if you carry out the well known blind-spot test (look at a cross drawn on paper with a zero drawn further away; whilst simultaneously keeping one eye closed and moving the paper away from you it appears as if the zero has disappeared. Move further still and the zero re-appears, this time with a grey middle). Input is needed from both eyes to gain a comprehensive understanding of our surroundings. If one eye is suddenly made redundant, the brain will attempt to ‘fill in’ the detail that has suddenly been lost. It is plausible that our brains do something similar with our memories.

It may be possible that the phenomenon of déjà vu is inextricably linked to memory. The brain may create a memory, but over time specific details are lost. When an individual encounters a very similar situation, what remains of that initial memory may be recalled and compared to the current situation. The brain attempts to recall those ‘lost specifics’, but cannot (as they have been forgotten). In this sense, the brain can be likened to the Daily Mail: in order to cover up the lack of data, the brain will insert specific details from the current situation – leading to that familiar sense of déjà vu, where a past memory seems identical to the situation you are currently in.

To make this explanation somewhat less confusing, let’s relate the roles of memories in déjà vu to a toy. One day you build a simple Lego house out of multicoloured bricks, placed in a random order of colours. This house represents an intact, freshly made memory. Over time, that memory becomes more distant, and some specific details may be lost – in the case of the Lego house, segments of the house are lost. One day you see another Lego house. It looks eerily familiar. At this point your brain will recall what is left of that initial memory. By now it has lost individual bricks, or even a chimney stack. However, the brain will attempt to recreate that past memory by simply using information on what it perceives at that present moment – essentially the memory will have copied segments of the current Lego house. This would be like re-building your initial house using the new house as inspiration – copying exact segments of the house, even down to the last brick. All of a sudden you become convinced that you have seen this house before, that you have experienced this situation before!

Youths are more likely to experience déjà vu than their parents. A more active mind - one that can more easily recall distant memories - apparently makes for a more lucrative “memory regeneration machine”. Maybe this is why younger people are more interested in Lego. Now would be a good time to look at cigarette-munching John McClane and tell him “John. This shit hasn’t happened to you before. Trust me. Imagine a house made of Lego…”

Déjà vu - the decay of a Lego house memory?

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