Basic Neuron Questions

KP-PC k.p.collins at worldnet.att.net%remove%
Thu Apr 10 23:49:04 EST 2003


"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.

Naw - the Proof ain't heavy' - and it's been organized for decades -
all it requires is an academic Neuroscience group, somewhere, that
isn't 'afraid' to actually do Neuroscience.

K. P. Collins





More information about the Neur-sci mailing list