temporal memory

Christopher T. Lovelace CL1779A at american.edu
Fri Oct 6 11:20:56 EST 1995


Actually, I didn't say that LTM is _stored_ in the hippocampus (although I
wasn't really specific and I can see how one could get that impression).
I just mean that they are _consolidated_ by the hippocampus (which is what
it sounds like you are saying).
 
Chris Lovelace            cl1779a at american.edu
 
 
In article <44uht4$7sr at ping1.ping.be>
Stephan.Verbeeck at ping1.ping.be (Stephan Verbeeck) writes:
 
>On Fri, 22 Sep 95 09:02:54 EDT,
>CL1779A at american.edu (Christopher T. Lovelace) wrote:
>
>>As to what neural mechanisms underly these properties, I'm not sure.  Perhaps
>>a type of Hebbian learning?   When I learn a song, I often listen to a
>>recording over and over.  This repetition leads to consolidation into long-
>>term memory (hippocampus).  The memory itself, I would imagine, is stored in
>>cortex, in a fairly distributed fashion.
>
>Sorry but I must disagree with you because I have done a lot of research
>on this and came up with different results.  The current view (proposed
>by several books on the subject) that long term memory is stored in the
>hypocampus is completely wrong.
>
>Our brains is working on a pulse coded system.  These pulses flow in
>"strings".  The whole mechanism is based on the concept of free
>association.  That is the knowledge that two things are related without
>having to know HOW they are related.  Our brain is wiring together events
>and things in the order in which we perceive them either by direct
>observation or by thinking about them.
>
>Like this the brain is building strings of events and things that can be
>regarded as some kind of story (but it can just the same be a sequence of
>muscle actions to fire).
>
>If we see, hear, feel or smell something the first node of a string is
>activated.  Because humans have developed in to a "smart" species that
>can think about events when they are long gone we need a "device" to fire
>pulses in those strings.  A string can be activated by an external event
>(e.g.smell) but to activate the complete string and all related strings
>connected behind it that draw pulses from the first one a lot more pulses
>are needed that the external event will provide.   The hypocalamus is
>doing this.   The amount of pulses put out by the hypocalamus is more or
>less constant over short periods so that the amount of strings that can
>be "kept alive" is also more or less constant.  If a string (thought) is
>finished and none other are active then the hypocalamus (we call it pulse
>source in AIR1NN (which is a revised kind of NN that mimics the behavior
>of biological neurons)) will activate new strings almost at random
>(mostly already partially activated by being related to the previous
>thoughts).  This is why your thoughts never stop.  If an external event
>is activating new strings then this new string will "suck" on the
>connections to the pulse source so that the pulse flow is redirected to
>the newly activated strings.  If there are to many new strings activated
>or they draw to much pulses (several strings starting from the newly
>activated one) then the stream of pulses to the previously active strings
>will stop completely and the person will "forget" what he was doing
>before and continue with the new stream of thoughts.
>
>This is an oversimplification but our memory works by association.  In
>other words it will put out anything that is related to what is put in
>into the network of strings.  In the example of driving a car each next
>action to take is related to the place where that action took place
>earlier.  This is a very very powerful retrieval system but it also has
>one great disadvantage.  You already need to know at least a part of what
>you want to remember.  There are also other problems that could be more
>easily solved in software then in a biological unit (human/animal).  So
>the future is to the computers (Don't shoot, I don't like it either).
>
>If the hypocampus is damaged the amount of pulses that is needed to train
>our biological neural net (each pulse is one training) can not be
>achieved for "internal" strings.  Internal are all strings that are not
>almost directly connected to external events (senses).  So without
>hypocalamus you can still learn new motoric skills.  Forming abstract
>strings require the pulse source to provide the amount of training needed
>to form new memories (alter synaptic connection strengths).
>
>The hypocampus plays also a very important role in sleep and our response
>to chemical stimuli.  Pain can (even when more local and imprecise)
>replace the hypocampus for learning because pain is nothing else then an
>enormous external pulse source.  So pain will increase the short term
>learning skills dramatically.  In the long run it is a bad alternative
>since this amount of pulses is to powerful to get the strengths in the
>neural network right.  The network will "over-learn" the activated
>strings.  The same is happening during "normal" learning (when awake) so
>that we require regular sleeping periods during which the pulse source is
>reactivating the strongest connections (over-learned strings) because
>these are at that moment the strings with the smallest "resistance"
>(strongest neural connections).  These strings are then supplied with a
>small amount (30% of awake) of pulses.  This amount is not enough to get
>the entire string activated (charges decay after a few seconds) so that
>the charges (pulses) are spreading more evenly to all connected other
>strings.  Like this connections (other then the over-learned ones) will
>also fire so that those will become better and the over-learned a bit
>weaker.
>
>To understand how this is working I must first explain that the output of
>a neuron is also an input.  A neuron will fire if the charge in the
>front-chamber (dendrites and the "body" of the cell) exceeds a threshold
>compared to the back-chamber (axon).  The potential of the axon is the
>potential of its environment.  If a second neuron (which dendrite is
>connected to the axon of the first one) is firing then that second neuron
>will have a negative charge in its front-chamber after firing.  This in
>turn will cause the charge of the axon of the first neuron to become less
>so that the first neuron will fire easier as long as that condition
>exists.  This effect is causing some kind of "vacuum" that is sucking
>charges from previous neurons.  The longer the string of firing neurons
>formed this way the stronger this effect becomes (that is also how the
>pulses from the pulse source end up connected to those strings).  However
>this only takes place if the next neuron fires.  If you keep the amount
>of pulses over time low then you will not activate many of the next
>neurons in the string(s) because the charge decays before it can build
>up.
>
>So in practice the distribution of pulses from a neuron to the next ones
>(all other neurons who's inputs connect to the output of this one) is
>determined by:
>
>1) The neural weights of the connections.  The better (stronger) the
>connection the easier that next neuron will fire.
>
>2) If one of the next neurons has fired shortly ago then the connection
>to that neuron will seem to be better for a short time because of the
>negative charge in the front chamber of that particular next neuron.
>
>Because of (2) a string will form.  In other words: The pulses will chose
>a path and stick to it until forced otherwise.  In a "normal" neural
>network (AI software) all of the next neurons get some of the value of
>the previous.  In our brain this is not happening.  A few (mostly only
>one) of the next neurons get all of the pulses and the remaining non at
>all.  Current NN software only mimics behavior (1) and not behavior (2).
>It only works by calculating distribution of charges (values) but that is
>not what matters.  What matters is the path that the pulses are choosing
>(what I call a string).  However if (2) happens then (1) will change to
>adapt to the behavior of (2).  So if a path is formed then the strength
>of the neural connections will change in favor of those that form the
>path of the pulses.  This effect can not be turned of in our biological
>neural nets so if we repeat a movement or thought very often then it will
>become over-learned.  So the next night we will dream of those
>over-learned movements or thoughts (yes AIR1NN needs dreaming).  Before
>this "leveling" of neural connections (during sleep) can start all
>activity has to stop first because if there are still strings active then
>the pulse source will feed those (many pulses to a few strings) instead
>of providing wide-spread low-level activation (few pulses to many
>strings).  After a while (can not happen fast because charge decay times
>are same as awake) those over-learned connections will become less
>good/strong (strong connection=small resistance).  Once this has happened
>there will be no favor for particular strings to receive pulses from the
>pulse source (hypo calamus) so that normal operation of the network
>resumes.  That means that strings start to activate again in sequence in
>the order in which they are connected together forming thoughts similar
>to and in the order of those real experiences.  While that is taking
>place the pulse source if activating less strings with more pulses until
>the level of activation is reached and effect (2) star ts to work again.
>And then we wake up.
>
>Of course there is a lot of chemical influence on the hypocalamus to
>force start and end of sleep but it all fits nicely together.
>
>- awake(over-learning)
>  (pulse source at 100% with variations from
>  50 to 200% (rest to nervous/aggressive))
>
>- first-sleep(period of non-activity)
>  (pulse source at 5%)
>
>- first-dreaming(dreaming about things done that day)
>  (pulse source slowly 5->30%)
>
>- REM-dreaming(thoughts become more story-like)
>  (pulse source at 30% increasing -> 50% to wake up)
>
>So as you can see theory and observations match nicely.
>
>This is becoming a long story and there is a lot more to tell that is not
>related to the question of the original poster so if there are any more
>questions, things that you think are wrong or comments... feel free to
>send me a mail.  If you wish I can also mail you a copy of earlier
>articles and postings on this subject.
>
>With kind regards,
>
>
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