Dirk Wessels <d at wxs.nl> wrote:
> The reason that I am looking for data is that I have slightly different
> theories about the organisation of neural networks.
> This organisation seems to use some kind of waves and synchronisations
> in which emotions seem most important.
I think this may be the start of an interesting discussion.
> Some of the many questions that I have:
> 1) Are these neuron connected to amplify wave properties and how.
Neurons may be excited and inhibited in synchrony (tens or even hundreds
of thousands of neurons being in phase). The simultaneous change in
membrane potential relates to the simultaneous influx into the cell of
ions, or outflux. The actual event on a molecular level is the swift passage
of ions through a single channel in a membrane location in a single
cell. When we discuss a whole cell or a group of cells, however, the net
movement of charge in the volume conductor of extracellular fluid does
look like a "wave" of change in electrical field. Often such "waves" are
synchronous (examples: alpha rhythm of the thalamocortical network, '40
Hz' rhythm of the same, theta rhythm of septum-hippocampus, etc.
Sometimes they are less regular like the delta waves of sleep, but if
they have a large amplitude they still are based on the simultaneous
movements of charge in many neurons.
These various "waves" must first of all be regarded as results of the
synchronous activation or inhibition in neuronal groups. The basic
result is that many neurons simultaneously signal forwards along their
connections, and transmission between neurons is mainly through the
(quantal) release of chemical transmitter molecules. Reverberating
circuits with more rhythmic properties arise through the feedback
coupling in neural networks. Whether the "waves" or "fields" have any
stimulating property in addition to the basic neurotransmission through
signal molecules is an old, and rather unresolved question.
Your question about calcium "waves" is more understandable now.
Calcium ions do move into neurons, and are pumped out; the channels
through which calcium enters and exits are numerous and their regulation
is largely known. In some circuits, like the thalamocortical network,
calcium channel opening has a central role in determining the functional
state of the network.
> 2) is a chemical process going on that has wave properties.
Beats me. Som many chemical processes influence the basic function of
neurons (excitation and inhibition by incoming transmitter actions, the
possible crossing of the action potential treshold, the coupling of
action potential to calcium influx in nerve terminals, the release of
transmitter due to this). In this functional cascade there are, in each
neuron, hundreds of sequential chemical steps, each with several or tens
of parallel pathways. At each point in each step, the input-output
relation can be and is indeed varied from situation to situation.
I suppose the flow of chemical reactions in a group of neurons can be
regarded as a "wave", but I doubt that this is what you have in mind.
> 3) What sychronises or influences the timing of these waves and other
> signals.
Convergence is the phenomenon that SEVERAL different effects may
coinciditently excite or inhibit ONE target. Divergence is the
phenomenon that ONE element may affect SEVERAL targets. One suffiently
activated element may thus simultaneously affect numerous others. Mostly
a coincidence of several specific things happening at the same time in
the same location ( a coincidence detector) starts a cascade where the
effect (the chemical reaction in a cell, or the response of a cell group)
is much stronger than the original triggering signal. Given suitable
feedback coupling, a reverberating circuit may be activated (leading to
a rhythm), and given lateral coupling between similar neurons, the
simultaneous action of all these neurons may be started.
> 4) Are any quantum-level processes involved to help in timing or
> sychronisation.
I would not know. We used to call transmitter release quantal, i.e. one
action potential released a number of transmitter 'quanta', and the
smallest quantum was the transmitter content of one storage vesicle.
However, this is not necessary true any more, as virtually everything is
graded.
> 5) How can we simulate these neural networks more exactly, especially
> the learning process.
Personally, I think that the advances in neurophysiology during the last
decades has made simulation infinitely more difficult, as there are no
more simple input-output relations. Fuzzy logic, coincidence detectors
and escalating cascades (catastrophe theory) might be important
elements.
> 6) Why are emotions and waves important at all.
Emotions are biologically important :-)
Waves are more doubtful. What waves? They might be just epiphenomena of
the signalling mechanisms that ARE important.
I still think that a good introductory text might help you more than the
comments you can possible get on the net. While Kandel, Schwartz and
Jessell (eds.): Principles of Neural Science (Appleton & Lange) is the
normally suggested text, their smaller: Essentials of Neural Science and
Behavior is in my opinion quite satisfactory as an introduction, and the
recent favourite of mine for this purpose is Bear, Connors and Paradiso:
Neuroscience, Exporing the Brain (Williams & Wilkins). Shepherd's
Neurobiology (Oxford University Press) is also a good book with a
different style.
Dag Stenberg
------------------------------------------------------------------
Dag Stenberg MD PhD stenberg at cc.helsinki.fi
Institute of Biomedicine tel: (int.+)358-9-1918532
Department of Physiology fax: (int.+)358-9-1918681
P.O.Box 9 (Siltavuorenpenger 20 J)
FIN-00014 University of Helsinki,Finland
------------------------------------------------------------------
