Electric Field Effects in the Brain?

r norman rsnorman_ at _comcast.net
Sat Apr 19 16:21:43 EST 2003


Note: my comments are all at the end

On Sat, 19 Apr 2003 19:26:26 GMT, "KP-PC"
<k.p.collins at worldnet.att.net%remove%> wrote:

>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)
>wrote:
>|
>| >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...
>| >
>| >Thanks,
>| >YKY
>| >
>| >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,
>or
>| any organ of the body for that matter, is salt water with a very
>high
>| conductance.  The electric fields in either the intracellular or
>the
>| 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
>that
>| makes ephatic interaction between nerve cells so ineffective.  Only
>if
>| the adjacent cells are extremely close and only if there is some
>| special confinement of extracellular space (as, for example,
>wrapping
>| 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
>ionic conductances.
>
>| Growth cones are influenced by electric fields.  You can produce a
>| strong enough field with special experimental chambers and
>electrodes.
>| It is difficult to produce that strong a field with external
>| radiation. People routinely work in areas of very high electric
>field
>| 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
>existence.
>
>I'll Appreciate your comments.
>
>Cheers, Richard, ken [K. P. Collins]
>
You make two points.

First: about glial cells.  Yes, they can influence nerve activity
through their metabolic activities and by afffecting the ion
concentration in the extracellular space.  But the original query was
about electric fields.  The effects you mention do not work via that
mechanism. 

Second: about 3D neural topology.  Yes, of course the nervous system
is highly organized and is most definitely not a "blob".  However, the
organization is cellular and the structures are separated by cell
membranes.  These have a time constant on the order of, say, 10 msec.
Therefore, for AC electric fields with frequency larger than 2 pi/tau
or about16 Hz, the boundaries between cells don't really matter.
Especially for frequencies high enough to be effectively radiated, the
brain is for all intents and purposes a bowl of salt water mush.
Again, my only concern in my post is with electric field effects.
Basically, what I was arguing is that, although there are electric
fields in the brain, "electric field effects"per se really aren't very
significant in the way that nerve cells function.

You have a third point about the significance of energy dynamics
which, frankly, I don't follow especially since I haven't been
following your numerous posts.  But again, if whatever it is you mean,
it is not electric fields and so is not relevant to the original
query.



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