I'll Appreciate your discussion, Richard.
"r norman" <rsnorman_ at _comcast.net> wrote in message
news:gtv2av0l7fo5opblku4n3lbteof7f6pa2l at 4ax.com...
| On 18 Apr 2003 20:26:19 -0700, y.k.y at lycos.com (yan king yin)
|| >Inside the brain there are ubiquitous fluctuations of
| >electric fields of magnitude ~100mV, due to nerve impulses.
| >Most of the standard connectionist models of the brain
| >do not take this effect into account. Is this some noise
| >that can be ignored?
| >I think one way to know the extent of the significance
| >of this E field is to induce some random ~100mV E fields
| >externally from the scalp, and see if they wreck the
| >mind =)
| >Can anyone point me to some references or facts...
| >P.S. Personally I know of 2 instances. One is the
| >"ephatic coupling" of parallel nerve fibers that tends
| >to synchronize nerve impulses. Second is the effect of
| >E fields on growth cone dynamics. Both of these theories
| >are not very mainstream it seems.
|| There are fields and there are fields.
|| The 100 mV potentials you describe are specifically across the
| cell membrane. If you want to talk about electric fields, 100 mV
| across a 100 A membrane (10 nm) gives a field strength of some
| 10,000,000 V/m. It takes a pretty decent dielectric to hold up
| against that!
|| However, these potentials are in specific locations caused by
| sources that have the proper impedance characteristics (channel
| conductances) to produce the necessary current. Most of the brain,
| any organ of the body for that matter, is salt water with a very
| conductance. The electric fields in either the intracellular or
| extracellular spaces are very small. It is very hard to induce
| potentials in these media from externally applied fields because of
| the high conductance.
|| It is, in fact, the high conductance of the extracellular medium
| makes ephatic interaction between nerve cells so ineffective. Only
| the adjacent cells are extremely close and only if there is some
| special confinement of extracellular space (as, for example,
| by a common glial cell) can current densities reach a high enough
| level to produce an electrical potential that significantly alters
| cell function.
I disagree. During the course of long-term 'focused' neural
activation [as is the case in devoted problem-solving activity]
conductance gradients build because, for instance, glia act as K+
electrodes which instantiates K+ distribution, which alters 'resting
potentials', which alters action potential energydynamics - which
results in altered nervous system function that's traceable back to
| Growth cones are influenced by electric fields. You can produce a
| strong enough field with special experimental chambers and
| It is difficult to produce that strong a field with external
| radiation. People routinely work in areas of very high electric
| intensity without any hint of mind altering events.
The fact that, if 'memory' is to occur, one thing that =must= occur
is that 'growth cones' =must= exhibit trophic dynamics having
specific correlation to the neural activation that actually does
occur within a nervous system, points directly to a necessary
coupling to the net energydynamics inherent.
Yes, there are 'molecular' dynamics involved, but as I've discussed
in other threads, these, too, =must= be rigorously-coupled to the
energydynamics inherent in the activation that actually occurs within
the nervous system, else the molecular dynamics would be
'superfluous' with respect to 'memory' and 'learning', and therefore,
'without consequence'. But why would evolutionary dynamics leave =so
much= supposedly 'inconsequential' stuff within nervous systems, all
of it consuming energy that's only be going to Waste?
The 'point' I'm discussing is at the most-Fundamental 'level' of
nervous system function - but it's 'where' everything is
tied-together ['where' everything within the nervous system becomes
rigorously coupled, not only with respect to it's various
'components' and processes, but with respect to energydynamics
external to the nervous system.
In other words, if external physical reality is to be 'known', then
the internal energydynamics have to be coupled to the external
energydynamics 'all the way down'. ["It's activation dependence all
the way down, not turtles." :-]
With respect to your thoughtful discussion of conductances, a factor
you left out is the that the 3-D neural Topology, itself, greatly
restricts energy's freedom to move within a nervous system - co
'conductance' doesn't occur as a 'blob'. It occurs in the
highly-restricted way that's Determined by the 3-D neural
architecture. Relatively-repetitive 'pumping' within
activation-defined regions of the 3-D neural Topology [as occurs with
respect to 'focussed' neural activation] results in
increasingly-restricted energy's freedom to move. Then, all
'learning' has to do is 'follow' the energy-gradient inherent, and
undergo trophic dynamics that rigorously reflect such.
It's not a 'blob'. Conductances are not 'willy-nilly', but
extremely-restricted by the fact of the 3-D neural architecture's
I'll Appreciate your comments.
Cheers, Richard, ken [K. P. Collins]