"Rich Cooper" <richcooper1 at mindspring.com> wrote in message news:<a3pfjd$b8k$1 at slb5.atl.mindspring.net>...
[snip an awful lot of old stuff to try to keep to one point]
[Rich Cooper]
> I'm simply responding to
> the Science News article that seems to indicate there is some kind
> of message being transferred in an impulse other than a simple
> on/off message. Given that speculation, I'm trying to explore how
> such a message might be encoded and transferred among neurons.
>
Yes, I did indicate that there might be more than on/off when I wrote:
[Richard Norman]
> > Although we say the AP is "all-or-none", the fact is that
> > different action potentials differ in details of amplitude and duration
> > and after potential and such depending on the history of
> > firing, the metabolic state of the cell, the chemical
> > environment (ion concentrations), possible
> > activation (phosphorylation) of membrane channels, etc. And the details
> > of the amplitude and time course of the AP in the presynaptic terminal
> > can be important in determining just how much transmitter is released.
> > Some synaptic modulators work by altering the presynaptic AP in just
> > this way.
[Rich Cooper]
> The original question here was about what frequencies were adequate
> for an encephalogram database. I'm trying to add to that question the
> possibility that higher frequencies might lead to better understanding
> of the content of the encephalogram. Specifically, the types of messages
> (if they exist at all) could depend on the types of stimuli that would be
> part of any encephalogram database. If the frequency bands recorded in
> the database are much higher than the normal clinical signals, they can
> be used to explore the kinds of stimuli (visual, auditory, linguistic, ...)
> presented to the subject, versus any subsequent diagnosis, and possibly
> could add to the quality of the database.
You are technically correct in saying that to properly record the
time course of the action potential, you need sufficient bandwith
(sufficiently high frequency range) in the recording apparatus. Many
details of shape and duration are contained largely in the higher
frequency components of this bandwidth. That is certainly well
understood by all who do such recording. And maintaining the
necessary high bandwidth in the face of parasitic capacitance and
high microelectrode resistance is a well-known problem. But when
you talk about "encephalogram database" I believe the general
assumption is that you really mean "electroencephalogram database"
and the EEG is an entirely different story. It typically has only
very low frequency components -- perhaps to a few hundred Hz if
that while unit recordings with microelectrodes go into the 10 kHz
region. If you are interested in variations in the action potential
that might produce variations in synaptic transmission, an
"encephalogram" simply is inappropriate. In fact, there are
pitifully few locations in the CNS where you can even begin to
think about examining the details of the synaptic mechanisms.
Your discussion about different stimuli presented to the subject
(visual, auditory, linguistic ...) is incommensurate with the
notion of thinking about events at individual synapses. They
are on such different "levels of organization" that they are
(at this time in our knowledge, at least) completely separate
subjects.
[Richard Norman]
> >Many weird things do happen in biology. And
> > we can dream up many even weirder things. But experimental scientists
> > tend to completely discount any imaginings that cannot be tested
> > experimentally.
[Rich Cooper]
> Its easier to postulate mechanisms to be tested experimentally if you
> have data to study. Any quality encephalogram database should provide
> more opportunity for study, leading to those imaginings!
>
There are no shortage of mechanisms to be tested experimentally and
there is already more data to study than we have skills and techniques
to devise the appropriate experiments. Your questions, even the
entire tone of your approach, is quite commonly found in physical
scientists and engineers approaching neurobiology without a solid
experimental biology or physiology background. Only certain types
of experiments are possible and there are enough mechanisms to
study that are barely beyond our current techniques. It simply is
not a useful way of spending time to consider a few dozen more
hypotheses that are well beyond our ability to even begin to
examine the mechanism.