neurotransmitter storage (all or one?)

Theophilus Samuels theophilus.samuels at btinternet.com
Wed Aug 30 13:03:21 EST 2000


Greetings Dag,

I apologise for the lack of clarity on my behalf.

Firstly, the statement

> Theophilus Samuels <theophilus.samuels at btinternet.com> wrote:
> > That is a very blunt statement - where is your evidence that processing
(see
> > later) occurs on all levels of the neuron??

was actually in response to the comment

> > As far as I know there is processing at all levels of the neuron.

My main concern about this sentence was the use of the word 'processing'.
And the third paragraph that you quoted attempted to explain what I see as
'processing'. Let me try again. At this very moment, you are processing
these words within your brain (via digital inputs, and perhaps analogue as
well) and they are being consciously interpreted by some unknown mechanism
allowing you, or the self, to understand (hopefully ;-)) what I am writing.
Here it becomes difficult to explain, so bear with me.

In theory, you could have as many digital inputs/outputs as you like that,
when attached to an appropriate interpreter, are able to produce desired
responses - like a computer and a program, in fact. The key thing to
remember here, is that the digitial input/output mechanism is a well-defined
operation - it either happens or it dosen't, there's no messing around [I
will come back to this again later]. Now let's look at the analogue way of
processing things. By definition, as has been stated in past postings, an
analogue system works by using a continuously variable quantity, such as
voltage or pressure. And thus, by assigning certain tasks to specific states
of this variable the desired response is carried out by the system - ok?
Now, to what scale is the variable quantity divided into in order to assign
specific tasks to each of these states? Obvisouly, the smaller the scale, or
the more it is split up into, the more can be carried out by the system. Let
us now turn to the neuron. I of course agree completely with what James Teo
said about the actual physical content of the brain: the 'ion channels in
the synapses to the ion channels in the nerve fibres, the protein machinery
as well as the grading distances at synapses and neurotransmitter diffusion
rates, and even glia'. But there is a big problem here with regards to
information processing, can't you see it? If we deal with just a single
neuron, what can we label as the continuously variable quantity about a
graded response that will make the neuron analogue? How about the potential
difference across the dendritic membrane? Sound good? OK, which part of the
dendritic membrane? How small should this area be? How far along should it
be from the point of origin? Should we also take into account the number of
ions taking part in the response? You see how many variables there are for a
single variable ;-). Imagine the problem when dealing with several hundred
or thousand of these neurons. How can I make the following point any
clearer - intuitively, I believe an analogue system that uses these kinds of
components produces far too much randomness for it to be processed or
interpreted into an orderly coherent 'self'. How can the brain interpret
signals and respond with constant responses (like the colour of this writing
is black) when each graded response is always different from the other?

My thinking is as follows. I tried to introduce a concept earlier on, but
no-one seemed to notice. The concept was Frequency coding. As stated, the AP
is an all or nothing event, to requote 'it doesn't mess around'. Now here
lies the difference between the randomness of an analogue system based on
graded responses (this was the original argument) and that of this one -
TIME. If we have 5 AP being fired by a single neuron, the time intervals
between each of them could be more easily collected and processed. But now I
hear you say, we have no element in our brain that counts time on such small
scales! And quite right so. Here lies a big leap of faith, the brain somehow
knows how to interpret these signals. But surely that's as random as the
previous example I hear you protest! Well actually, no. Why? Because a
neuron does not fire unless it, without being to simple, has or is forced
to. In other words, (I've probably lost you by know) something about the
neuron (the unsolved mystery) makes it special so that its prime physical
function, AP generation, is kept unique. By the introduction of time,
frequency coding emerges. This may be all that is needed, or indeed
something else is required, who knows?

Hell, we could discuss this all day, needless to say, many will disagree. Oh
well, never mind.

T.L.S.

This sentence is a lie


<dag.stenberg at helsinki.nospam.fi> wrote in message
news:8oiasl$5rv$1 at oravannahka.helsinki.fi...
> Theophilus Samuels <theophilus.samuels at btinternet.com> wrote:
> > That is a very blunt statement - where is your evidence that processing
(see
> > later) occurs on all levels of the neuron??
>
> in response to James Teo <james at pc.jaring.my>, who wrote:
> >> In essence each neurone is a distinct computer performing many
different
> >> calculations and passing it on in a digital and analogue fashion.
>
> I am not going to try to verbalize badly what has been written clearly,
> but let me say that I find Theophilus Samuels' comments confusing, e.g.:
> > Let us clarify something - that of the concept of information
processing. At
> > this moment you are reading this paragraph. What is happening? To cut it
> > short, binary information, yes, 0 and 1's, are being transmitted to key
> > areas within the brain. Now, how is this information processed into the
> > reality that you and I are faced with. That is, the apparent ability of
us
> > all to read and understand the meaning of the words in this paragraph -
the
> > consciouss experience if you will? That is what the original discussion
was
> > about - is this further processing done in a digital or analogue manner,
or
> > using a mixture of both of them, or by something completely different?
>
> whereas the words of  James Teo <james at pc.jaring.my> make perfect sense
> to one who has read modern neurobiology:
> >> As far as I know there is processing at all levels of the neuron. From
> >> the ion channels in the synapses to the ion channels in the nerve
> >> fibres, the protein machinery as well as the grading distances at
> >> synapses and neurotransmitter diffusion rates, and even glia. In
> >> essence each neurone is a distinct computer performing many different
> >> calculations and passing it on in a digital and analogue fashion. I
> >> don't see how this would prevent a silicon-based brain simulation
> >> since you could have each neurone function as a virtual program with
> >> protein, ion channel, conductance, etc subroutines passing information
> >> to another virtual neurone according to various modifiable rules
> >> (representing synapse-buoton size, synapse distance, glial
> >> interactions, receptor density, etc). The information passed on is
> >> graded, but the activity on the other virtual neuron may be any
> >> combination of digital and neural depending on the rules.
>
> This makes sense because a neuron really does not operate as a
> all-or-nothing (binary) device except when sending signals over a
> distance (as has been pointed out before). A neuron reacts to input
> exactly in all the ways James Teo lists. In that respect, I find the
> analogy correct that each neuron can be modelled by a vast number of
> binary devices. For any axonal output (action potentials) to be
> meaningful, they must be regarded as the binary decision of a complex
> chemical machinery, wheres thousands of simultaneous and parallel
> protein conformation changes (resulting from energy flow, enzymatic
> action etc.) provide the intracellular signalling. Some reactions
> provide a lot of amplification (one molecular change leading
> to a great amount of ensuing changes), but sometimes only in the case of
> coincidence of several signals.
>   A bit of Basic Neurochemisty might be useful to read. In my youth
> neurophysiologists tended to focus on "nerve impulses" and potential
> changes - since then the understanding of neuronal function has leaped
> into the molecular era, and nothing has become less interesting in the
> process.
>
> Teophilus Samuels asked what turns this information processing into
> conscious experience, and "is this further processing done in a digital
> or analogue manner, or using a mixture of both of them, or by something
> completely different?" I suppose one could say that the mind-body
> problem is still unsolved, but that there is still reason to believe that
> conscience "emerges" from the concerted action of the various neuronal
circuits
> in the brain - but now we know that a neuron is a very complex chemical
> machinery also, and no neuron can be modelled by a signle binary
> element. Who cares? Personally I do not see how the "emergence" of
> conscience gets any easier or more difficult to understand if we know
> more in detail about neuronal molecular function. However much we know,
> the bridge between single chemical reactions and emerging conscience of
> the whole will be as difficult to grasp.
>   As for digital modelling of brain function, my impression is that the
> advances in knowledge about brain function during the last decades show
> that computer modelling is lagging more and more behind, that is, we
> begin to understand that the computers of any age up to the present
> (and there has been a slight development in computers also since the 60's)
> are capable of modelling only a smaller and smaller fraction of the
> biological knowledge which is available at any time.
>
> - Sorry for my limited ability to verbalize thoughts.
>
> Dag Stenberg
> ------------------------------------------------------------------
> Dag Stenberg     MD PhD                    stenberg at cc.helsinki.fi
> Institute of Biomedicine    tel: (int.+)358-9-1918532
> Department of Physiology                   fax: (int.+)358-9-1918681
> P.O.Box 9        (Siltavuorenpenger 20 J)
> FIN-00014 University of Helsinki,Finland
> ------------------------------------------------------------------
>







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