[Neuroscience] Re: A Purely-Electronic Brain -- Possible?

r norman via neur-sci%40net.bio.net (by r_s_norman from _comcast.net)
Sat Apr 21 09:56:51 EST 2007


On 21 Apr 2007 06:21:48 -0700, "rscan from nycap.rr.com"
<rscan from nycap.rr.com> wrote:

>On Apr 19, 4:00 pm, r norman <r_s_norman from _comcast.net> wrote:
>
>> Physical scientists, mathematicians, computer scientists, and
>> practitioners of various arcane trades that bear little resemblance to
>> science have difficulty understanding that "the brain" is living
>> matter.  Action potentials are the easiest thing to "see" about brain
>> activity and so, goes the mistaken general idea, if we recreate the
>> action potentials then we recreate the brain.  Action potentials are
>> probably the least important of the brain's machinery and large
>> numbers of neurons function quite happily without being able to make
>> action potentials at all.  That the life of the cell has anything to
>> do with the function of a neuron is seemingly incomprehensible.
>
>Very, very, very smart people have looked at the brain and could not
>understand it. Therefore, they concluded the brain must be the most
>complicated structure in the universe, well past understanding. They
>may be right, but maybe not. Some, who are only very, very bright, say
>the answers may be found in quantum mechanics. They, too, may be
>right, but maybe not.
>
>On action potentials: The workers in central pattern generators
>(CPG's) seem to be very happy in a world of action potentials. Their
>diagrams are instantly recognizable to an electrical engineer. The CPG
>people claim to understand a tiny piece of brain. I give them the
>benefit of the doubt.
>
>I am aware of amacrine neurons and ephaptic effects, even gap
>junctions. Still, I think that action potentials are useful aids to
>understanding. Don't knock them.
>
>> And, it might be mentioned, just what are all those  glia doing, just
>> holding the neurons  together (and apart)?- Hide quoted text -
>
>We may take the position that the nervous system is an entity,
>separated from the exterior universe by an interface. The interface
>has two parts: One is composed of the sensory neurons. One is composed
>of the motor neurons. All the cells of the organism, other than nerve
>cells, belong to the exterior universe. The glia are external.
>
>I find great utility in this position. I recommend it. It is a natural
>extension of the Bell-Magendie Law. Don't knock it.
>
>Incidentally, the interface runs through the pituitary.
>

I certainly don't knock the action potential.  Any time a signal must
travel more than a millimeter or so, it must be in the form of an
action potential.  It is just that within one cubic millimeter of
brain tissue, there may be thousands of neurons and tens of thousands
of synapses that can function quite well on local potentials.  There
are innumerable dendro-dendritic synapses in local microcircuits that
work without action potentials.  In the retina, the rods and cones,
horizontal cells, and bipolar cells work without action potentials and
the amacrine cells mostly do, too.

Pretty much all the central pattern generators that I know about rely
very heavily on non-action potential mechanisms to produce patterned
rhythmic activity.  These are usually local semi-active potentials due
to calcium conductance changes that modulate cell activity.  

When glial activity interacts and modulates neuronal activity, then
they certainly are not "external" to the nervous system.

There do exist groups who are very active in modeling true neuronal
activity, including local potentials, synaptic modulation, calcium
effects, the whole works, in a method that tries to be as true as
possible to physiological reality.  On the other hand, there are
people who model artificial "neurons" and build all sorts of complex
networks from them with no or little regard to physiological reality.
Both types of work can accomplish important results, each in their own
arena.  I just don't care for the claim that AI work on "neural"
networks has much connection to actual brain function.

Then there are people (Penrose comes to mind, here) who make (or have
made) arguments like: "We don't understand consciousness.  We don't
understand gravity.  We understand everything else in the world of
physics and physics explains everything.  Therefore consciousness must
rely on theories of gravity."




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