Re: New Scientist on memory

From: Dace (edace@earthlink.net)
Date: Sat 31 May 2003 - 19:58:18 GMT

  • Next message: joedees@bellsouth.net: "Re: New Scientist on memory"

    > From: "Lawrence DeBivort" <debivort@umd5.umd.edu>
    >
    > Recalled from what?

    From the past. Memory is the recall of events from the past. This is the common sense view, and it's rapidly becoming the only viable scientific view as well.

    > From: joedees@bellsouth.net
    >
    > > Though the author himself doesn't seem to realize it, the evidence
    > > discussed in this article abolishes the notion that the brain alone is
    > > responsible for memory. Every time we recall something, the relevant
    > > memory trace in the brain is completely erased and then
    > > "reconstituted" from scratch. If memory is nothing more than stored
    > > information in the brain, there would be no way of recreating the
    > > memory once it's been erased. The only explanation is that we
    > > literally recall the past (often making mistakes in the process)
    > > enabling us to reconstruct the memory after the neural trace has been
    > > destroyed. Memory must be taken at face value-- as a recollection of
    > > the past-- rather than simply the retrieval of information from
    > > cerebral vaults. We may regard neural traces as pointers to memories
    > > rather than the memories themselves.
    > >
    > > --TD
    > >
    > The article states that memory is not 'erased' so much as it is
    > 'redynamized';

    Let's take another look at the article:

    > To study memory consolidation, researchers interfere with steps in the
    > fixing process in order to test their influence on long-term recall. While
    > doing this kind of work, researchers including Karim Nader of McGill
    > University, Montreal, and Joseph LeDoux of New York University noticed
    > something odd. They trained rats to associate an electric shock to their
    > paws with a darkened box. The rats learn that the box is "nasty" and
    freeze
    > the next time they are put back. If, a few days after training, the
    animals
    > were given a drug to stop protein synthesis before being reminded of the
    > conditioning stimulus - the sight of the training box - it made no
    > difference to their ability to remember it. The memory seemed fixed and
    > safely stored. But if the rats had a brief reminder of the stimulus just
    > before the drug was given, then a memory that should have been fixed and
    > stable seemed to be erased.

    Every time you remember something, the relevant "memory trace" in your brain is erased. Ordinarily, you simply re-establish the trace, perhaps in modified form, in the act of recalling the event from the past. But if something interferes with your ability to re-establish the trace, such as a drug that stops protein-synthesis, you lose the memory. The trace, which had already been erased, is now gone for good. It's in the gap between recall, when the neural trace has been liquidated, and the moment the trace is re-established, that the true nature of memory is revealed. During that gap, your brain cannot help you remember. It's up to you.

    > But if the rats were reminded of the sight of the box just before the drug
    > was injected, the result was precisely the opposite. Now the
    > protein-blocking drug created amnesia.

    When you recall something-- and the memory trace is instantly destroyed-- you can still remember the event, but if you lack adequate protein to re-establish the trace on the basis of your recollection of the past, you'll never remember it again. The next time you try, the neural trace will be gone, and you'll have no way of "tuning in" to the memory.

    > At both the synaptic level and the anatomical level, it was as if the
    > consolidated memory had been released and needed to undergo the whole
    > fixing process again if it were to be remembered.

    If memory is contained in the brain, and the neural trace has been
    "released," how can the memory be fixed again? On what basis is the "fixing process" carried out? It can only be on the basis of our recall of the past event itself.

    Memory requires two things: 1. a memory trace in your brain to point you to the memory 2. your direct recollection of the past, on the basis of which you re-establish the trace for later recall.

    > The protein filaments that give
    > the cells their internal shape have a half-life of just a few minutes. And
    > the receptor proteins that stud the synapses need replacing every few
    days.
    > As Joe Tsien, a neurobiologist at Princeton University in New Jersey,
    says,
    > the brain you have this week is not the one you had last week. Even the
    DNA
    > needs to be repaired. So if "you" are essentially a pattern of synaptic
    > connections, a tangled web of memories, then there is a big problem of how
    > this pattern endures. "I don't know how people ever got this static
    picture
    > of the brain," says Tsien. "A memory trace would have to be a dynamic
    thing
    > just because of molecular turnover."

    Memory is the basis of enduring self-identification. If memory were nothing more than a pattern of synaptic connections, our sense of enduring selfhood would indeed be illusory. But the pattern of synaptic connections is not the memory itself, any more than "88.9 FM" is identical to the songs you hear when you tune in to that frequency. Enduring self-nature is not an illusion. We are not auto-hallucinations.

    > And the more you think about it, the more such dynamism makes sense.
    > Susan Sara of the Pierre and Marie Curie University in Paris, who found
    > indications of a reconsolidation effect in her own experiments in 1997,
    says
    > the real problem for the brain is not how well it can preserve the past
    but
    > how successful it is at integrating new learning with old learning.
    Memories
    > exist to make sense of the present - to recognise and understand the
    world -
    > and the brain needs to be able to optimise all its circuits, strengthening
    > or generalising some connections while weakening or erasing others.
    > Reconsolidation may seem a radical and unnecessary step for a brain that
    > just wants to be a dormant warehouse. But, Sara says, if a memory becomes
    > completely plastic every time it is roused, then it can be refiled in a
    > carefully updated way. Active choices can be made about whether to merge
    > the old and the new - or by contrast, to reinforce their separateness.

    What kind of a storage system allows for stored information to become
    "completely plastic" every time it's recalled? Wouldn't it make more sense to simply modify it each time instead of erasing it and "reconstituting" it from scratch? Sara is right about the importance of memory remaining fluid so as to keep up with ever-changing contexts. And this is why memory is not based on a storage system.

    I think memory research is in a kind of twilight zone right now. Researchers are unwilling to give up their old views despite the fact that we now know memory is irreducible to the brain, and a neural storage system doesn't even make any sense in the first place, given the demands for flexibility. It just goes to show that a meme-- in this case the culturally-ingrained habit of considering memory in terms of neural information-storage-- is currently stronger than our ability to examine this issue reasonably.

    Ted

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