[From Bill Powers (920710.1330)]
Bruce Nevin (920710.1342)
In this really rather complex chain of inter-cellular relationships,
does one cell in the chain control the next, with respect to the
transmitted neural current?
If cell A controls the neural current in cell B, then according to the
definition of control, an independent perturbation of the neural current
emitted by cell B should result in a change in neural current from cell A
that has an effect equal and opposite to that of the perturbation. As a
result, the neural current emitted by cell B should prove resistant to such
perturbations because of the action of cell A.
I don't think that this is how synapses work: nothing that happens to cell
B affects cell A at all (i.e., backward through the synapse). If the neural
current in cell B is disturbed, cell A will simply continue to send its own
signal into cell B in the same way as before. So the signal from cell A
INFLUENCES the neural current emitted by cell B, or where it is the sole
influence, DETERMINES B's neural current, but does not control it.
Now, dropping back a paragraph or two:
Each constituent cell of an ECS is in itself blind to the functioning
of the ECS. Nor does it in any direct sense control for helping to
constitute an ECS. Nor does it have any means for perceiving the ECS
of which it is a constituent.
Somewhere in here is an important observation -- I can't carry it all the
way through, but perhaps we're thinking along similar lines. You have some
provocative ideas here.
The individual (neural) cells that constitute an ECS are themselves
independent living entities. As you say, they know nothing of the larger
system of which they are the components. The variables for which they
control are only those that they can sense. The actions they employ for
control are those that affect the same variables. Disturbances that alter
the controlled variables are opposed by the actions of the system.
Guess: the controlled variables of a neural cell include the potential
inside the cell at the axon hillock. Incoming signals disturb that
potential. When the potential gets high enough, it is restored to the
acceptable level by the cell's firing. In the continuous-firing situation,
the cell's rate of firing has an effect on the average internal potential
that is equal and opposite to the average effects of excitatory incoming
neural signals. So neural cells react to disturbances by going through
repetitive electrical convulsions that keep the mean internal potential
near a reference signal specified within the cell, perhaps by its DNA. As a
side-effect, the cell emits neurotransmitters from the end or ends of its
axon. This may amount to getting rid of waste-products generated by its own
Neural cells clearly disturb the controlled variables in other nerve-cells,
in the process of correcting for disturbances FROM other nerve-cells. One
cell in the midst of a network thus acts on its environment, which in turn
(through external feedback paths) acts on inputs to the same cell. These
feedback paths have to be negative if the internal variable is to be
controlled via the external loop rather than running away to one extreme or
That leaves me stumped for the moment. So what? It occurs to me that this
approach is an attempt to deduce the existence of a higher order of control
systems -- the neural heirarachy -- by referring only to the reference
signals and control systems inside the cellular components of the larger
system. Can we get there from here? I'm thinking of neurotaxis, which seems
to be a phenomenon of a level higher than the cell. Can we express
neurotaxis in terms of reference signals and controlled variables inside
the cell itself? Could a cell that needs negative feedback from somewhere
emit a chemical signal from the spot where it's needed? Could a cell with
surplus neurotransmitter to unload grow itself toward a spot that wants and
can accept that kind of transmitter?
I think there's a limit to how far we can go with this kind of emergence --
maybe. The behavioral hierarchy gets most of its negative feedback through
the external world, where physical phenomena foreign to the body get into
the loop. And the effects of controlling for different external (that is,
sensory) variables in different ways are important to the body in places
remote from the controlling systems: in the stomach, the bloodstream, the
gonads, and so on. Something has to link these remote effects back to the
very organization of the behavioral systems (that's what my reorganizing
system is supposed to do). Could these remote effects get into the loop in
any meaningful way at the level of a single cell trying to maintain itself?
Somehow I think not: the effects of a single neural signal on the external
world, outside the body, would be lost in the general effects from all the
nerve-cells that participate in behavior. We're talking, I think, about a
much smaller-scale environment, including only a small volume around the
I have a strong sense of something important here that's considerably
beyond my reach.
The analogy to the human situation that you want to communicate is clear.
There is a system whose components are individual human beings. The
individuals know nothing of their role in the larger system; they see their
actions as affecting themselves only, and don't realize that the side-
effects are linking them to other people, loops and meshes of other people
that end up affecting the same individual. As the individuals seek to gain
control over their immediate environments, they adapt to the feedback
effects that include all the other people with whom they interact. These
adaptations, created by each individual simply for the purpose of
controlling local variables, keeping the sign of the local feedback
negative, give the system as a whole properties that aren't characteristic
of any individual, but only of the whole network.
The "whole network" is probably a lot of small groups loosely linked to
each other. Within the group with which an individual most closely
interacts -- like CSG-L -- the feedback effects are strong and immediate,
although in our case they're only verbal. The members of such small groups
adjust their means of action, their mutual disturbances, so each person can
control for what is important to that person, including how each person
wants the group to appear. Close-knit groups take on a character that is
recognizeable, particularly to those in the group but also to others. Hard
to describe, but familiar.
The groups interact with other groups. But there are fewer direct
interactions than among individuals in a given small group. The world-as-a-
whole group probably hardly merits the term.
Hearking back to previous discussions, there doesn't seem to be any reason
to think that at the group level and up the resulting organization is that
of a hierarchy of control. But there's certainly an emergent organization,
many of them. I think you're quite right in suggesting that whatever this
organization is, individuals know nothing of their roles in it. Not that
it's impossible to analyze -- but before it can be analyzed, one has to
understand that it's there.
Once again, I feel that you've made an important point that is for now
beyond my reach. So now I feel as if the bottom has dropped out and the
ceiling has been removed and I don't know whether to fall or fly.