neurotransmitter storage (all or one?)

dag.stenberg at helsinki.nospam.fi dag.stenberg at helsinki.nospam.fi
Wed Aug 30 01:51:01 EST 2000


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   
------------------------------------------------------------------






More information about the Neur-sci mailing list