DC lesion?

NMF nm_fournier at ns.sympatico.ca
Sun Feb 15 02:35:11 EST 2004


There are considerable differences between what I post and what you post.

Whether the effects from the DC stimulation are entirely local or can be
generalized to other regions is a matter of debate.   (I am not saying that
the current will actually flow some considerable distance away from the site
of injection and then stimulate other neurons.  First of all that would be
impossible physically. I am saying that the effect at a local site from the
current stimulation can evoke activity from the neurons at that site causing
them to modulate the activity of other distal target sites that may or may
not result in long-lasting changes in synaptic efficacy.  Is that clear?).

In response to your point on habituation.  The current is NOT directly
injected into the cell but is injected  extracellularly.  Prolonged low
intensity current stimulation (field stimulations) have been shown to alter
the expression of specific subunit configurational elements within ion
channels that are expressed by neurons within the vicinity of the
stimulation site (these changes are primarily on NMDA subtypes and sometimes
L-type voltage gated calcium channels) .  Moreover, these same neurons
eventually show less and less of a response over time to applied current
stimulations. You can record this easily in the laboratory.  This is an
extremely established finding and is well cited in the literature.  Maybe
this is a semantic issue with respect to using the term, "habituate", but
any time a system's response to some stimulation steadily declines to a
point of no responsiveness then employing the label "habituation" is and
would be extremely valid.   What habituates is the neurons' response to the
current.

Your term, "tuning-precision void", seems some what analogous but in my
opinion is extremely ambiguous at the same time because of the introduction
of a term like "void".  When you employ one of your terms in a discussion
that was not initially meant to involve theoretically explanations, then
make sure you define EVERY term properly and concisely.  Words are extremely
important and can construe your point if you do not adequately provide
sufficient explanation.  Using term (or terms) like "void" by definition of
immediately limit the discussion. Your theory, by the virtue of the terms
you employed- like "void"- are by definition non-measurable and then can
only be inferred and not directly tested or measured.  You could have
substituted a term like, "tuning-precision God", or some other derivative.
In either case, I or anybody in that manner cannot say it is wrong nor can
we say it is right. The choice of labels employed are by virtue directly
immeasurable and ambiguous.

 Moreover, employing your theories are not necessary since this finding and
discussion has been shown and explained a long time before any of us had
begun discussing this (for an example see Graham Goddard, "the original
kindler", work).   This is something that Klenow is most likely aware of and
isn't really the point of the discussion. Your comments that subtle
"supersystem configuration" 'abnormalities' post-DC-injection would occur is
something I completely agree with and I would say that supersystem
configurations is a good metaphor that basically means the results are from
the physical changes in the expression of specific ion channel subunit,
alteration in their firing dynamics, and indirect effects from the local
neuronal activity on their associated targets.   That is a mechanistic
approach to a ambiguous umbrella explanation, like "supersystem
configuration", that encompasses actual physical processes.



> Do you realize that, except for what I'll discuss below,
> you've just reiterated my previous discussion without
> integrating what you've reiterated?
>
> Although, if it continues indefinitely, it'll probably
> have physiologically-deleterious effects, there's
> nothing intrinsic in low-level DC that can be "hab-
> ituated" to. It 'just', local to its injection, shifts
> membrane potential, and everything else that
> occurs operates upon that shifted membrane
> potential, 'seeing' it as being 'normal' [which is
> what results in the "tuning-precision void" after
> the DC is withdrawn. And why there should
> also be subtle "supersystem configuration"
> 'abnormalities' post-DC-injection [see AoK, Ap5].
>
> K. P. Collins
>





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