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Explaining Déjà Vu

A short but interesting article at Scientific American discussing what is going on in the brain when we experience déjà vu:

Although scientists have not pinpointed exactly what goes on in the brain when a person experiences déjà vu, they can make good guesses based on models of memory. All theories of memory acknowledge that remembering requires two cooperating processes: familiarity and recollection. Familiarity occurs quickly, before the brain can recall the source of the feeling. Conscious recollection depends on the hippocampus and prefrontal cortex, whereas familiarity depends on regions of the medial temporal cortex.

…The best evidence for a neural mechanism for déjà vu, which around 60 percent of people experience at least once, comes from studies of patients who experience it chronically. In 2005 cognitive neuropsychologists at the University of Leeds in England described two patients with recurring and persistent feelings of déjà vu. The patients refused to read a newspaper or watch television because they felt as if they had already seen it all before. They found it difficult to shop for groceries because they thought they had just purchased those items. The researchers discovered that these patients had damage to their frontal and temporal regions. Harm to these areas likely caused the patients’ familiarity circuitry to fire frequently, even when they were in a novel situation. In undamaged brains, déjà vu likely occurs because of processing errors in these same regions.

Full article at Sci-Am.

Editor
    1. All over again
      [quote=earthling]There are other causes of déjà vu. In my case, my life is extremely boring, and I actually do do the same stuff every week.[/quote]

      Well, strictly speaking, that would not be ‘déjà vu’. That would be ‘life’.

      1. from the Intended-Intentions-Interest-Compounded-Dept.
        [quote=Greg][quote=earthling]There are other causes of déjà vu. In my case, my life is extremely boring, and I actually do do the same stuff every week.[/quote]

        Well, strictly speaking, that would not be ‘déjà vu’. That would be ‘life’.[/quote]

        Terry Prachett did a good bit on this (as well as other, marvelous things). From the 2006 movie adaption of his book Hogfather, where Death makes the observation

        “Human beings make life so interesting. Do you know, that in a universe so full of wonders, they have managed to invent boredom.”

        So, strictly speaking, I think that would be not paying enough attention to life, universe, and everything.

  1. Brain as computer

    Harm to these areas likely caused the patients’ familiarity circuitry to fire frequently, even when they were in a novel situation. In undamaged brains, déjà vu likely occurs because of processing errors in these same regions.

    Oh dear, oh dear. The brain is a computer of course. It has circuitry like a computer. It has processes like a computer. I suspect that this is more than an analogy with these guys … it is the only model they are comfortable with (today). Just like those old diagrams of cogs and wheels in the head in the days before computers. They need a physical mechanism.

    They say it themselves: what they are looking for is “The best evidence for a neural mechanism for déjà vu …”. Implied but unspoken is the base assumption that consciousness itself is a product of some neural mechanism. We are supposed to take that as read.

    Dave.

    1. My Mum had brain surgery a
      My Mum had brain surgery a long while ago and they cut through the bit correlated with processing sound. Apparently we all had robot voices for several days while the brain ‘rewired’ itself around the damage. There was no tonality in anyone’s voices.

      These correlations are interesting. Whether the damage to the brain in these parts is creating the sensation is hard to say from this, as ever, correlation is not the same as causation.

      I don’t have the same problem with the metaphor of the brain as a biological computer though, but I’m excited to see if in 20 years the metaphor is still standing.

      I guess the easy question to start with is whether we have identified any closed causative system where we can explain a piece of brain functioning. It reminds me of where that imagine was read from neurons in the visual cortex. I don’t know whether that would be enough for an example, I imagine it is quite complicated, but I am still amazed. Besides the difference between classical computing and quantum probably means the term ‘computer’ is quite wide.

      1. computers
        There are actually many kinds of computers that process data quite differently. The familiar CPU-Memory-Disk type is just the most pervasive. Substantially different approaches exist physically and many more as theoretical models. What most people call “classical computing” is more strictly a Random Access Machine. According to Stephan Wolfram, the world is another type of computer, a Cellular Automaton. There are many others.

        The brain is sort of analogous to computers in the sense that it does process information, so it does some of the same things computers do. For those things, it is fair to say that the brain is roughly equivalent to computers. We can see how some processing happens, and we can observe the results of some of that processing going wrong.

        Personally I don’t believe that “processes” is a good term to use for the brain functions that are localized and persist over time. The word “process” in computing has a specific technical meaning, and the brain processes are not like that.

        Also the brain most certainly is not a Random Access Machine. There is no central processing going on, and there is no central processor. There isn’t a (large) group of central processors either. In fact, there doesn’t seem to be anything central about it, it all seems to be distributed. But then again not distributed uniformly either. There is structure, but it isn’t hierarchical, with one thing at the top deciding what to do.

        It gets even more interesting, there isn’t even one single underlying control mechanism in the brain. Some control comes from specific neuron states. Other control comes from hormone levels. And then there are the interesting cases of parasites affecting the brain, and resulting in very specific decisions being made by the parasite’s host. How does that work?

        1. We are the cat 😉 I think
          We are the cat 😉 I like that.

          Anyway…

          I like all that. It will be interesting to see what comes of the idea of quantum processes occurring in neurons instead of fully macroscopic processes, but anyway.

          What you say above is why I have no problem with the idea of the brain as a computer. Obviously nobody means like a personal computers motherboard, they mean in in the same sense as when the universe is compared to a computer, it is in certain senses, and not in others.

          The fact is that in alot of senses the metaphor holds true, and in the senses that it doesnt it doesn’t really matter since it isn’t a fixed term. It is just as good as comparing the internal structure of the Earth with an onion, in fact ticking off comparisons it is much more accurate.

  2. Déjà Vu a form of Precognition?
    I don’t often get the feeling of déjà vu, but every few years or so I will have an episode, and they are particularly strong.

    In one instance, I had the feeling of déjà vu so strongly in the middle of a conversation I was having, I started saying all parts of the conversation (from the four participants) as the other participants were saying it, so it was in Stero, with two mouths in synch saying the same thing. I felt so strongly that I had lived the conversation before, I even knew what everyone was going to say. Obviously it freaked everyone out, including me, and wasn’t discussed again.

    Could déjà vu be the manifestation of seeing the future, prior to events occuring, even if just a few seconds into the future? I don’t know but that’s sure what it felt like at the time.

    ASM

    1. I experience déjà vu maybe
      I experience déjà vu maybe once a month, but I have not had an episode like AncientSkyMan. To know what people are going to say must be very weird.
      I usually just get the strong feeling that I have done what I am doing before, or been to a place before (that I have never been to). The usual kind of déjà vu i guess.

      Must be hard living with cronic déjà vu like the people in the article. Feeling that you have done everything in your life before you do it..

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