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Medical Memory limited to the technique used? or to the 'space' left in the brain.?

  1. Feb 7, 2010 #1
    Hi I originally posted this at yahoo ans but I guess I may get ans. from professionals here.
    source yahoo ans:http://answers.yahoo.com/question/i...Pzw6GfYazKIX;_ylv=3?qid=20100207115304AA4Du5m
  2. jcsd
  3. Feb 8, 2010 #2
    I have never heard it asserted that there is a space limit to memory. I don't think anyone could confidently make such an assertion because, to the best of my knowledge, no one is certain exactly how memories are stored.
  4. Feb 9, 2010 #3
    You are right that how exactly memories are stored, no one knows.
    But it is generally believed that the no. of neurons are limited and therefore the information stored in the brain is limited. Like you are kind of consuming Space in the brain when you are saving information in neurons in the brain.

    I think I didnt explain my question clearly, its unorganized and very long.

    Let me make it easy.

    It is believed that humans use only 10-20% of their brains. When someone in future may use 100% of their capacity, their memory will be full and they wont be able to remember more. The condition will be like a computer hardisk(lolz) which gets full. Now you may know how to put more information in it but the problem is there is no space left in the harddisk.

    Do you think the brain will evolve at such a point.

    P.S: I was just reading on the internet and I came to know that it is recently known that we use 100% of our brains always but different parts of the brain are doing different things. So where is memory stored then?
  5. Feb 9, 2010 #4
    I don't know where or how memory is stored. I do know that the hippocampus is the single most important part of the brain as far as laying down memories is concerned, but that doesn't mean memories are stored in the hippocampus, just that they're stored by the hippocampus. On the other hand, there is an important class of memory called "procedural memory" which seems independent of the hippocampus. So it's complex.

    As far as the number of neurons goes, here again, any limit depends on how memories are stored. The fact there are only three primary colors does not limit the number of different paintings that can be painted using them.

    In his book Musicophilia Oliver Sacks reports that brain scans show that imagining music, hearing a song in your head, causes the same regions to be activated as listening to real music. This suggests that memory is a sort of degraded replay of the patterns of neuronal firing that happened during the original experience. That implies that there is no limit whatever to memory because there's no limit to original experiences, each of which will cause their own pattern of neuronal firing over time.
  6. Feb 9, 2010 #5


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    Forget the percentages.

    We use all parts of our brains, but never all of the capacity all at the same time, we only use small amounts and different areas at different times. Does that make it clearer?
  7. Feb 9, 2010 #6


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    Some ideas:

    J Vis. 2009 Oct 5;9(11):3.1-30.
    No capacity limit in attentional tracking: evidence for probabilistic inference under a resource constraint.
    Ma WJ, Huang W.
    Human ability to simultaneously track multiple items declines with set size. This effect is commonly attributed to a fixed limit on the number of items that can be attended to, a notion that is formalized in limited-capacity and slot models. Instead, we propose that observers are constrained by stimulus uncertainty that increases with the number of items but use Bayesian inference to achieve optimal performance. We model five data sets from published deviation discrimination experiments that varied set size, number of deviations, and magnitude of deviation. A constrained Bayesian observer better explains each data set than do the traditional limited-capacity model, the recently proposed slots-plus-averaging model, a fixed-uncertainty Bayesian model, a Bayesian model with capacity limit, and a simple averaging model. This indicates that the notion of limited capacity in attentional tracking needs to be revised. Moreover, it supports the idea that Bayesian optimality of human perception extends to high-level perceptual computations.

    Nat Neurosci. 2007 Apr;10(4):485-93. Epub 2007 Mar 11.
    Limits on the memory storage capacity of bounded synapses.
    Fusi S, Abbott LF.
    Memories maintained in patterns of synaptic connectivity are rapidly overwritten and destroyed by ongoing plasticity related to the storage of new memories. Short memory lifetimes arise from the bounds that must be imposed on synaptic efficacy in any realistic model. We explored whether memory performance can be improved by allowing synapses to traverse a large number of states before reaching their bounds, or by changing the way these bounds are imposed. In the case of hard bounds, memory lifetimes grow proportional to the square of the number of synaptic states, but only if potentiation and depression are precisely balanced. Improved performance can be obtained without fine tuning by imposing soft bounds, but this improvement is only linear with respect to the number of synaptic states. We explored several other possibilities and conclude that improving memory performance requires a more radical modification of the standard model of memory storage.

    Neuron. 2007 Apr 19;54(2):319-33.
    A neural circuit model of flexible sensorimotor mapping: learning and forgetting on multiple timescales.
    Fusi S, Asaad WF, Miller EK, Wang XJ.
    Volitional behavior relies on the brain's ability to remap sensory flow to motor programs whenever demanded by a changed behavioral context. To investigate the circuit basis of such flexible behavior, we have developed a biophysically based decision-making network model of spiking neurons for arbitrary sensorimotor mapping. The model quantitatively reproduces behavioral and prefrontal single-cell data from an experiment in which monkeys learn visuomotor associations that are reversed unpredictably from time to time. We show that when synaptic modifications occur on multiple timescales, the model behavior becomes flexible only when needed: slow components of learning usually dominate the decision process. However, if behavioral contexts change frequently enough, fast components of plasticity take over, and the behavior exhibits a quick forget-and-learn pattern. This model prediction is confirmed by monkey data. Therefore, our work reveals a scenario for conditional associative learning that is distinct from instant switching between sets of well-established sensorimotor associations.
  8. Feb 10, 2010 #7
    Very interesting abstracts, atyy.

    The assumption in them seems to be that memory boils down to the old "neurons that fire together, wire together", that memory is inherent in the fact that once having fired in a certain configuration, neurons will 'prefer' to fire in that configuration. This means that the 'where' of memory is wherever neurons have fired in response to a stimulus. "Plasticity" seems to refer to the ability of neurons that are already a part of a 'preferred' pattern of firing to participate in a new pattern, in response to a new stimulus. Any given neuron, in fact, must be able to participate in multitudes of different patterns.

    The limits on memory would not be a matter of storage space at all, since 15 billion neurons can result in a near infinity of different configurations, but a matter of "slow components" superceding "fast components; more solidly laid down patterns over-writing and erasing more fleetingly captured "quick forget and learn" patterns.

    Does that square with your understanding of what's happening?
  9. Feb 10, 2010 #8


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    I think this still implies a limit when you consider the overwriting of old memories. I don't remember a lot about my first 15 years, for instance. Just little things that I've remembered rememebering consecutively, making the memories less reliable each time I imagine them.

    Eye witness accounts are known for their lack of reliability because of the way we add to and take from our memories when we remember (imagine) them.
  10. Feb 10, 2010 #9
    All true, but the Op is interested in deliberate learning:

    "This is only in regard to memory that you intentionally remember, eg. facts. "

    The limit to what can be deliberately memorized, is probably a function of the health of the hippocampus, and neurons in general, all of which declines with advanced age, and not a matter of "space". The brain has no hard drive that can be filled to capacity. Personally I would suppose that deliberate memorization of facts with the intention of being able to remember them any time you need them for the rest of your life, is probably the hardest kind of memory to over write.

    On the other hand, deliberate memorization of facts with the intention of being able to recall them, say, two weeks later for the midterm, but at no later time, may cause these to be over written much sooner. I think we often stamp a kind of shelf life, or expiration date, onto memorized information. There's no point in me remembering that 30 years, two months, and 23 days ago, I had a dentist's appointment at 3:30 P.M. at Dr. Stickndrill's office, 3343 E. 3rd St, 2nd floor, Office 214. Haycity, Arkansas.
  11. Feb 10, 2010 #10
    Thank you all so much all, especcially Zoobyshoe!!

    I learnt how human memory works is different from the way a hardisk memory works. I thought it's the harddisk way, reading that you(zoobys) have never heard about a space limit to memory I now understand that I have been mis-interpreting information that I read.

    This is what I understood. Memory is formed by combination. When there are 3 neurons containing different basic information eg. primary colors. Different combinations of these 3 neurons (i think using synapses) creates different colors(new information)! The number of connections you can make is limited to the logical limit i.e. red+blue=purple or any color formed by combining the 2 colors only.

    I also notice this is also what mnemonics is based on. You have to concentrate on arranging information and finding logical links between them. If memory would be like harddisk, we would not need to arrange and link information to remember(which we all do consciously or subconsciously), we would just have to tell the mind to put in and take out information as we do with a harddisk as much as the limit of the hdisk allows.

    This is a good read related to memory-http://learnmem.cshlp.org/content/3/5/341.full.pdf"

    Last edited by a moderator: Apr 24, 2017
  12. Feb 11, 2010 #11


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    But there are things we intend to remember forever. I still remember the 12 traits from boy scouts, but I don't remember the oath. I learned both with the intention of always remembering them. This is of course antedotal, but I'm curious what sets them apart.

    I'm also curious how we can justify saying that there's no limit. Is it possible, for instance, that we simply couldn't fill our quota in a lifetime?

    My assumption is that a limited number of neurons have a limited number of configurations between them, but I'm also not accounting for recursive operations. Do biological neural networks have recursive properties?
  13. Feb 11, 2010 #12
    I am not sure. I think if you're really interested in finding out why you saved one and discarded the other, a Freudian type analysis would uncover a link between the oath and something you weren't eager to remember. (Like I, personally, quit the Cub Scouts because an annoying "copycat" joined my troop, simply because I had joined, and because he felt it gave him a justification to be my pal. He ruined the experience for me and I had no choice but to quit to get away from him. Now I don't remember any of the Cub Scout rigamarole.)

    Yeah, all I'm saying is that our neurons probably start to degrade way before we reach the limit of firing configurations.
  14. Feb 12, 2010 #13


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    Haha, so I looked up the oath:

    "On my honor, I will do my best
    To do my duty to God and my country and to obey the Scout Law;
    To help other people at all times;
    To keep myself physically strong, mentally awake and morally straight."

    I've gone through agnosticism to atheism since being in the boy scouts and I never did like the idea of church and state in the same sentences. I remember now how much the oath reminded me of the pledge of allegiance (in a negative way). The Freudian analysis is surprisingly consistent. I must admit I was skeptical when I went to look it up.
  15. Feb 12, 2010 #14
    Let's test it though. What are the 12 traits that you do remember? Any religious ones?
  16. Feb 12, 2010 #15


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    Yeah, I thought about that:

    trustworthy, loyal, helpful, friendly, courteous, kind, obedient, cheerful, thrifty, brave, clean, and reverent.

    Reverent can be interpreted both in a religious and secular manner. I'm not sure how I saw it when I was learning it, but it's defined religiously in the Boy Scout manual (from what I found online).
  17. Feb 12, 2010 #16
    The religious "reverent" is probably easier to gloss over in the list form of the 12 qualities. You can easily rattle them all off without pondering the meaning of any, like reciting the times table. The oath, less so, since it's fully formed sentences. So, I'd have to agree that you probably have located the reason you started neglecting to reinforce your memory of the oath, and maybe even repressed it.
  18. Apr 4, 2010 #17
    Theoretically, memory capacity is bound by the plastic properties of the brain -- the brain's incredible ability to change physically (i.e., create new synapses) in response to learning or damage. There are two types of memory, declarative memory and procedural memory.

    Declarative memory involves the hippocampus and Papez circuit, and you use this memory when, for instance, you study for exams. Emotional experiences are particularly easy to remember.

    Procedural memory, on the other hand, involves the basal ganglia and cerebellum, and allows you to fine-tune your movements, allowing you to make that perfect free-throw.

    And, please, do not cite the 10% myth. People have speculated as to where this myth originated, and I favor the view that some self-help guru wanted a "scientific" slogan to support his work. "We only use 10% of our brains" may be a reference to human _potential_, but from MRI studies alone, we neuroscientists can tell you that we use all of our brains.
  19. Apr 5, 2010 #18


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    I wrote this on the 10% myth for Lancet Neurology......

    It is a well known “fact” that we use just 10 percent of our brains. This is why creativity gurus are always urging us to learn to tap the other silent 90 percent. It has also been a staple point for those who want to argue that consciousness has little to do with brain circuitry and more to do with some intangible soul-stuff.

    So where did this particular old wives’ tale spring from? Well, there are at least three famous bits of neuroscientific research that have fed the myth. And here are the modern countering arguments.

    In the 1920s, the behaviourist psychologist Karl Lashley carried out an experiment in which he trained rats to run a maze and then chopped away increasing amounts of their cortex to find out which grey matter bump might house the memory trace for the route. Lashley was surprised to find that what counted was not which part he cut out, just how much. So the memory seemed evenly spread over the brain tissue.

    Today we can answer that memories are indeed distributed across the cortex – though not evenly, but in a hierarchically organised fashion. The visual aspects of a memory will find their way to visual areas of the cortex, olfactory cues to the olfactory regions. And while parts of the brain like the hippocampus are specialist memory organs, they play a role mostly at specific stages like the fixing and recalling of memories.

    Furthermore, Lashley’s study did not even cut into lower brain centres like the basal ganglia which would have carried the most habitual or over-learnt aspects of the response. We now know that any kind of mental activity is the result of a team effort by the brain’s hierarchy and so damage to one area normally degrades rather than eradicates the ability to perform.

    Of course, Lashley was no fool and rightly concluded that his experiment merely showed that brain organisation was far more dynamic and distributed than existing theories recognised (Lashley 1930). But the indelible image of almost brainless rats still running mazes encouraged others to wonder if the cortex really did anything at all?

    Then in the 1930s, the pioneering Canadian neurosurgeon Wilder Penfield probed the brains of his patients with an electrode while operating on them for epilepsy. Such surgery is carried out while the patients are conscious and able to talk about what they are experiencing. The probing is done to ensure that surgery is not cutting into any vital areas like the language centres.

    Famously, Penfield found that jolts to some regions sparked vivid imaginary scenes or surges of emotion. But equally he was puzzled that there were large areas of "silent" cortex where he got no reaction. Penfield later came to argue that this uncertain connection between physical stimulation and mental response meant that there must be more to being a mind than just a set of brain circuits (Penfield, 1975).

    The modern view on these silent regions is that Penfield was simply using too crude a stimulus to stir the more delicate integrative parts of the cortex. Again, the brain being a distributed hierarchy, it seems that while the lower processing areas, such as the primary sensory cortices, will respond quite readily to an electrode, trying to interpret it as a real sensory event, the higher areas need to be hearing from a wider range of inputs to start to find any concrete meaning in them.

    Nevertheless, vivid newspaper accounts of Penfield’s and Lashley’s work helped foster the myth that much of the cortex, our wrinkled grey hemispheres, appeared mysteriously unused, or at least not completely necessary for everyday mental function. Einstein even jokingly declared that these untapped regions of the brain must be the secret of his own success, showing just how quickly this factoid entered into popular folklore.

    However today when anti-abortionists argue before Parliamentary committees about foetal sentience and cortical development, or psychologists rail against research linking IQ to brain volume, it is the research of an English neurologist, John Lorber, that still really gets them going.

    In the 1970s, Lorber was part of a world-leading spinal surgery team at Sheffield Children's Hospital treating kids with spina bifida. A frequent complication of this complaint is hydrocephalus where the fluid-filled ventricles in the middle of the brain expand, causing the cortex to be squashed against the bone of the skull. This can leave sufferers severely mentally handicapped or even kill them. Lorber was inserting shunts – plastic valves – to drain the cerebral fluid and so relieve the pressure.

    What surprised Lorber was that a few of his patients showed no outward sign of mental deterioration and yet X-rays revealed "wall to wall" ventricles. The chambers had ballooned to such an extent that there was barely any cortex visible inside the skull.

    The most celebrated case was that of a 26-year-old student at the University of Sheffield who had an IQ of 126 and a first-class honours degree in mathematics. This was despite a cortical mantle apparently crushed to paper thinness, the usual four or five centimetres having been reduced to a bare millimetre or so. Lorber estimated that the man's whole brain weighed only about 100 grams compared to the adult average of about 1500 grams.

    So an honours student with a brain mass not much more than that of a dog or monkey! Little wonder that Lorber was moved to ask: "Is your brain really necessary?" when talking up his findings at medical conferences. Or that the journal Science headlined with the very same question when it picked up on the story (Lewin 1980).

    The X-rays did make many people wonder what was the point of millions of years of careful evolutionary tuning to develop the very large and complex human brain if it still worked just as well when reduced to no more than a slick of neural tissue.

    Lorber’s claims were never publicly refuted. And Lorber - who died in 1996 - stuck firmly to his story, claiming that in 500 CT scans he had found many hydrocephalics with hardly any brain left above the level of the brainstem and yet living ordinary lives (Lorber, 1981). So a little detective work was needed to get to the bottom of this one.

    Talking to colleagues and contemporaries of Lorber, it was revealed he was probably greatly exaggerating the extent of brain loss in his cases. Said one source: "If the cortical mantle actually had been compressed to a couple of millimetres, it wouldn't even have shown up on his X-rays."

    Another agreed, adding that brain scans with modern techniques such as MRI (magnetic resonance imaging) show stretching, but not much real loss of brain weight with slow-onset hydrocephalus. He says the brain structure adapts to the space it is allowed: "The cortex and its connections are still there, even if grossly distorted."

    Sufferers with hydrocephalus also report many subtle symptoms that don’t show up in standard tests of cognition. They do well on basic reading and arithmetic or IQ-type questions, but struggle with focused attention, spatial imagination, general motor co-ordination, and other skills that rely on longer-range integrative links across the brain.

    This fits a picture of a brain in which all the cortical processing regions are in place but where the white matter – the wealth of insulated connections that actually occupies much of the centre of the cerebral hemispheres – has been pulled out of shape.

    So Lorber’s results were striking but overplayed. And certainly the rise of neuroimaging over the past decade ought finally to have put paid to this long-running myth about the 10 percent brain. One of the most important lessons from the first scanning studies of brains actually caught in the act of thinking – with areas lighting up with increased metabolic activity – was just how widespread were the patterns of activation for the most minor mental responses. No areas were silent, just relatively active or inactive in forming the reaction to the moment.

    As Lashley came to realise, the brain is not a simple device but a complex organ whose supple logic we are only beginning to be able to appreciate. New kinds of causal thinking are needed to model systems in which there is a localisation of function yet also global cohesion. Nevertheless you can be pretty sure that without any special effort on your part, you are indeed using the whole of your brain the whole of the time.


    Lashley KS. Basic neural mechanisms in behavior. Psychological Review, 37:1-24 (1930).

    Penfield W. The Mystery of Mind, Princeton University Press (1975).

    Lewin R. Is your brain really necessary? Science, 210:1232-4 (1980).

    Lorber J. Is your brain really necessary? Nursing Mirror, 152:29-30 (1981)
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