IUBio

Wavelet answer: Re: question: job of a neuron

John H John at faraway.com.au
Fri Sep 7 06:52:01 EST 2001


"Ron Blue" <rcb5 at msn.com> wrote in message
news:009301c1362a$6144a6e0$ce02030a at RBlue...
>
> Unfortunately, the rules we learned in school don't seem to apply to the
> real world.  Standard models are not standard, consider the summation
> in dendritic fields that would be dendrites talking to dendrites.
Normally
> information is thought to flow from dendrites to soma to axon to dendrites
> but this
> is not always true.  Neurons did not read the same rules that we
> did.  Consider the resent observation that glial cells transmit
information
> when we
> were told that their job was to support neurons.


It is nice and easy to say that neurons transmit, glia and astrocytes
support, but the division exists in our heads abstractly, not concretely.
Glia are important regulators of neural transmission and astrocytes probably
play some role also. For that matter, we need to remember that cytokines,
typically associated with immunological activity, also have a direct and
significant bearing on neural transmission. How does this all fare for
connectionist models of neural transmission, which imply direct signalling
as the only means of neural transmission?

For eg. Nitric Oxide. Nitric oxide acts as a neuro and immune modulator not
through direct contact but through diffusion to various regions in the
immediate cellular region. It has a half life of circa 30 secs and diffuses
rapidly, affecting not only the generating cell but often its immediate
neighbours. This effect on transmission will be contingent upon the distance
of the 'target' to the site of nitric oxide generation,
the rate of NO diffusion through the cell cytoplasm, and the general
metabolic activity of the relevant cells at the time. 'Excess' NO can make
all hell break loose then watch neural transmission struggle(the immune
mediated part). That's the trick though, the neural transmission can remain
intact for a very long time, all the while with neurons dying all over the
cortex and underlying metabolic processes  challenged.

The primary goal of brains is not to 'process information' but to generate
an appropriate response to environmental(internal and external)
contexts.Given the variety of metabolic contexts in which brains must
achieve this primary goal, I struggle with the idea that just observing
neuronal activity will give us ALL the insights into how neurons do their
work. The neuroscientists are well aware of this but too often I get the
impression that the AI people overlook this, preferring simply to think
about neural transmission as some
singular isolated process quite independent of the rest of the body. So I
wonder if Inhibitory neurotransmitters\modulators, which I believe increased
in frequency as brains became more complex, play a key role in helping to
control noise.

It is useful to remember that nervous systems evolved collectively, neurons
and glia and astrocytes all having their part to play, not to mention the
rest of the body. Nervous systems must not only contend with their own
internally generated activity(including sensations) but also contend
with\incorporate other signal types from the body that can signficantly
modulate neural activity. Whatever neural transmission is, it must be able
to cope with a plethora of signal types and volumes.

What I like about your approach Ron is that it provides avenues to
overcoming the continual noise and fluctuating contexts under which brains
must function. "Fuzzy processing" is the norm of brain function, not the
exception. What I would like to know is: can you test your model against a
simple nervous system?

John.















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