IUBio

Axon collaterals ?

kenneth p Collins kpaulc at [----------]earthlink.net
Thu Dec 18 02:05:51 EST 2003


"Joe Legris" <jalegris at xympatico.ca> wrote in message
news:3FE1091B.9030509 at xympatico.ca...
> nettron2000 at aol.com wrote:
> > Joe Legris <jalegris at xympatico.ca> wrote in message
news:<3FDFBB23.6060108 at xympatico.ca>...
> >
> >>Matthew Kirkcaldie wrote:
> >>
> >>>In article <Xns94539459E651FBilZ0rhotmailcom at 202.20.93.13>,
> >>> BilZ0r <BilZ0r at TAKETHISOUThotmail.com> wrote:
> >>> [...]

My comments apply to all neural dynamics.

What would be the worth of a hard-wired
response repetoire?

Zero - because it'd be unable to learn.

So all questions such as the current axon-
axon feedback mechanisms have to begin
with the understanding that the functionality
under consideration is learning-capable - that
is is not hard-wired - that it is plastic.

>From this beginning 'point', it's easy to see
that anything that's considered can have
widely-varying functionality, as long as it
instantiates learning.

If an axon-axon sub-circuit is to instantiate
learning [if it is to co-operate in learning],
it cannot do so via a hard-wired mechanism -
via a mechanism that always functions in a
single way - because mechanisms that can
only function in a single way cannot co-operate
in learning.

These considerations expose the need to
look deeper into the sub-circuitry that's be-
ing considered. One question is fundamental.
How is its functionality tuned so that it is
commensurate with the necessity of learning?

Seen through the 'lens' of this question, the
sub-circuitry being considered becomes
hugely more substantial.

There must exist mechanisms that tune the
functionality of the sub-circuitry - mechanisms
that, for instance, act to tune synaptic strength
at the site where the axon-axon feedback occurs.
This sort of tuning can occur in very 'mechanical'
ways, say, via glial contractile action that 'mech-
anically' adjusts the dimensions of the synaptic gap,
or, over a somewhat longert term, even selects the
synaptic Geometry [the site at which the axon-axon
synaptic contact will occur], or via glial ionic con-
ductances which tune the conductivity of the axon,
thereby adjusting the action of the feedback sub-
circuitry [kind of like an audia or video fade-in or
fade-out].

It's all very much more subtle than "here's a con-
nection, and it always does this or that".

If there's a feedback sub-circuit [or =any=
circuit], it's there for one reason: it enables
learning.

It's good to keep this one thing straight.

ken [k. p. collins]





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