IUBio

Wavelet answer: Re: question: job of a neuron

Richard Norman rsnorman at mediaone.net
Fri Sep 7 07:45:17 EST 2001


On Fri, 7 Sep 2001 21:52:01 +1000, "John H" <John at faraway.com.au>
wrote:

>
>"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.
>
I agree with most everything you say -- and it is very well put --
almost. Beyond your "liking Ron Blues approach (" do you really
believe in wavelets?) a technical quibble.  You speculate whether
inhibitory/modulatory processes increase in  frequency as "brains
become more complex".  Actually, inhibitory and modulatory processes
have been around for a very long time.  Consider the crustacean
stomatogastric ganglion, about the smallest known neural system (some
two dozen neurons).  It works entirely on inhibitory and modulatory
interactions between the cells.   You can't get "simpler" than that,
yet it is incredibly complex in cellular activity.  




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