Basic Neuron Questions

KP-PC k.p.collins at worldnet.att.net%remove%
Fri Apr 11 01:44:48 EST 2003


Hi John. Amateur\Professional - it makes no difference, because all
that's required is a nervous system with which to think - and we all
have one of these :-]

"John H." <johnh at faraway.xxx> wrote in message
news:8ksla.90$S06.4818 at nnrp1.ozemail.com.au...
| Richard, Didier,
|
| It's simple, it aint, ...
|
| I've learnt enough about neuro to appreciate Popper's comment, "We
may
| differ in what we know but in our infinite ignorance we are all
equal."
|
| So then, recalling,
|
| "Cortical neurons receive 3000-10,000 synaptic contacts, 85% of
which are
| asymmetric and     hence presumably excitatory...Absent any
inhibition, a
| neuron ought to produce an action potential    whenever 10-40 input
spikes
| arrive within 10-20 msec of each other...The neuron computes
quantities from
| large numbers of synaptic input, yet the excitatory drive from only
10-40
| inputs,     discharging at an average rate of 100 spikes/sec,
should cause
| the postsynaptic  neuron to     discharge near 100 spikes/sec.  If
as few as
| 100 excitatory inputs are active (of the 3000 available)    the
postsynaptic
| neuron should discharge at a rate of 200 spikes/sec.  It is a
wonder, then,
| that the    neuron can produce any graded spike output at all."
|
| Shadlen, M.N., & Newsome, W.T. 1998.  The variable discharge of
cortical
| neurons: implications for               connectivity, computation,
and
| information coding. Journal of Neuroscience, 18, 3870-3896

The problem with the above that it 'looks' at the 'trees' and doesn't
see the 'forest' - it looks at an extremely-delimited subset of
dynamics inherent in the global neural Topology, but doesn't see the
global neural Topology in which the extremely-delimited subset is
integrated.

With respect to the former, all that's necessary has been in the
Neuroscience Literature for at least 60 years.

With respect to the latter, all that's necessary has been in AoK all
along [~two decades].

So it really is Simple - read and understand the Neuroscience
Literature - read and understand AoK's synthesis of what's in the
Neuroscience Literature.

Any nervous system has, right within it, all that's necessary - but
such entails the doing of information-processing work.

So, with respect to the close-in stuff you've quoted, above, at a
gross [but nevertheless sufficient] 'level' of analysis, if it was as
the author said, none of us would, for instance, be able to type a
meaningful sentence because to submit our thoughts for discussion
here in b.n, because, n doing so, our nervous systems =must=
'eliminate' all neural activation that, if it were allowed to occur,
would result in some other stream of finger-hand-arm-trunk neural
activation [which are infinite in number [AoK, Ap1] than the one
through which our fingers 'dance' upon our keyboards to type out the
sequence of keystrokes that embody the information-content.

That we can see that we do, in fact, achieve such "finitized" [AoK,
Ap4] neural activation is =all= that's necessary to =eliminate= the
author's position from consideration - to see that it's flat-out
False.

What we've done is see the 'forest', and through such, we know that
the 'trees' are not as the author describes them. No need to waste
further energy considering the author's position.

It's just that simple.

| "The role of neurons in these computations has evolved conceptually
from
| that of a simple integrator of synaptic inputs until a threshold is
reached
| and an output pulse is initiated, to a much more sophisticated
processor
| with mixed analog-digital logic and highly adaptive synaptic
elements."
|
| Koch, C., & Segev, I. 2000. The role of single neurons in
information
| processing. Nature Neuroscience,  33,  Suppl: 1171-1177.
|
| Now I have no hope of understanding this and will gladly leave it
to you
| bods. Please feel free to elaborate. I'm an amateur, be gentle with
me. On
| the other hand, if you want a fight ... .

Again, that which can be demonstrated with respect to the 'forest'
=must= be integrated within any discussion of the 'trees'.

This's what's been in AoK all along. Folks deem AoK to be
'difficult', but that's not it.

The 'problem' has been that what's in AoK is just relatively
'unfamiliar' within 'tradition', so 'tradition' 'blindly' and
automatically 'moves away from' what's been in AoK all along.

This's why this 'problem' is AoK's main focus :-]

It's Simple.

Water is water. A horse is a horse.

A horse can drink, or not, but the horse's choice doesn't transform
water into something other than water.

It does determine the horse's survival, however.

Cheers, John, ken

| John H.
|
| "r norman" <rsnorman_ at _comcast.net> wrote in message
| news:incb9vkhq5unqqc48ed611939f8g25hp39 at 4ax.com...
| > On Thu, 10 Apr 2003 15:44:25 +0000 (UTC), "Didier A. Depireux"
| > <didier at rai.isr.umd.edu> wrote:
| >
| > >John H. <johnh at faraway.xxx> wrote:
| > >> Just for once, could someone say, "it's really quite
straightforward."
| I
| > >> wonder how often lecturers in neuro related jazz feel
threatened by
| their
| > >> students ... .
| > >
| > >So in a sense "it's really quite straightforward." The way you
phrased
| your
| > >question prevented me from saying that!
| > >
| > >What I mean is that, people have been arguing about whether it's
a time
| code
| > >or a rate code. And the truth seems to be a lot simpler, and
neither rate
| > >nor time codes. It's in between, one spike per relevant
time-scale.
| > >
| > >If an engineer had been asked to design a system using spikes to
| communicate,
| > >he would have chosen either a rate or a timing code of sorts.
The system
| > >designed by evolution is both more complex (because the relevant
| time-scale
| > >will depend on what is being encoded) and a lot simpler (you can
use the
| > >same coding scheme for any sensory input). It's economical
(precise
| timing
| > >requires a high metabolic rate, population code requires a lot
of
| neurons)
| > >and quite flexible.
| > >
| > >I don't know your background, John. But maybe you don't
appreciate how
| very
| > >very little we actually know about the brain. Our current brain
research
| is
| > >to a large extent like butterfly collecting. We arrange the
facts we
| observe
| > >according to their colors, size, shape, and put them in
different boxes.
| But
| > >at a fundamental level we have no idea.
| > >
| > > Didier
| >
| > Sorry to jump in so late on this thread, but there is a certain
noise
| > level here that makes it very difficult to follow the few posts
that
| > do actually  make sense.
| >
| > Didier's comments are quite sensible, but I disasgree that 'it is
| > really quite straightforward."  The problem is, as Didier says,
that
| > the nervous system was not actually designed -- it sort of just
came
| > out that way by evolution (the "intelligent-design folks
| > notwithstanding).
| >
| > It is easy for an engineer to take things like look sort of like
nerve
| > cells and create at least conceptual schemes where binary data
can be
| > transmitted by the details of timing in a spike train.  The
problem is
| > in showing that anything remotely like that actually happens in a
| > flesh and blood nervous system.  Even putting aside the
conceptual
| > difficulties of how to do it, the experimental difficulties of
finding
| > a preparation on which to test any hypothesis and then actually
carry
| > out the work is currently out of the question.
| >
| > Certainly there are specific cases where timing of nerve
activity,
| > even to the sub-millisecond level, is critical.  And certainly
there
| > are cases where a few interpolated spikes in a relatively steady
train
| > of a constant frequency can cause large changes in response
through
| > short term facilitation. But as a general rule, does critical
timing
| > really count or is only a rough running average of frequency
count?
| > For now, the latter seems like the usual way of coding.  Anyone
who
| > suggests otherwise has a heavy burden of proof to show that the
timing
| > mechanism is actually a general phenomenon in real, live brains,
not
| > in conceptual models.
| >
| >
|
|





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