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The hippocampus is =not= a 'spatial' map

NMF neil.fournier at sympatico.ca
Fri Jan 23 20:13:47 EST 2004


KP Collins:

Interesting concept.  That has some aspects that sound extremely similar to
both David Marr and Roll's idea of the hippocampus.  I have a few
clarification questions.  Could you explain in a little more detail what you
mean exactly by TD E/I(down) and TD E/I(up)?  (I have a vague sense but I
would like some information and perhaps some neurophysiological evidence to
suggest how such a process would occur normally within the brain).  When you
say the "blindly"-automated, do you disregard the account of pre-existing
synaptic weights and sliding threshold ("windows") potentials, that could
presumably alter the probability weights of certain incoming synaptic inputs
incoming into the hippocampus, and ensure that certain "information"
embedded with in this incoming input will be readily consolidated?  (this
concept does have experimental evidence, so I don't know what this means in
context to your model).

I like the metaphor of the hippocampus as a "traffic cop" (very clever and
astute observation).

One recent finding that I'm not to sure if you aware about, is that
neocortical traces require the reactivation of the hippocampus during
"remembering".  The recent work of Nader and LeDoux (2002) in a Neuron
paper, involving rodents.  They  showed that  presumably stabled contextual
fear information that were previously learned and considered to be now
distributed throughout the neocortex as a stable (or at least presumably
stable) representation,  that when the "trace" was re-activated again caused
the memory to return back to a "labile" state.  (A finding that goes against
Squire's concept that once memory has been consolidated and spread
throughout the neocortex, the memory is relatively "stable".... (I
understand that the word, "stable", may not be the best way to describe
memory and I cringe at the use of it now, but I am in lack of a better word
at the moment.  I definitely think employing concepts of memory as being
"stable" is a completely incorrect concept and goes against the years of
clinical experience showing the dynamic and often changeable nature of
memory.  i.e. Daniel Schacter has written extensively on the subject )).
Essentially Nader et al., found that the reactivation of the memory trace
caused it to return back to a labile trace becoming hippocampal-dependent
once again and requiring the hippocampus to "re-consolidate" the same
original trace.

The interesting thing is that the memory trace, even though it was already
associated with successful learning of the fear paradigm, could be
functionally inhibited with the microinjection of a protein synthesis
inhibitor into the hippocampus.  It obviously suggests that even though
presumably LTP-like processes and subsequent protein synthesis induced
modification to the cell ensembles had occur, reactivation of the memory
trace "countered" these changes.  Thus, if this reactivation processes was
some how inhibited the learned information will now be basically lost (or no
longer represented).  (Obviously, thinking about these concepts, if they are
really true and verifiable, the clinical implication of "reactivation"
therapy and accompanied electroconvulsive therapy following such treatments
have empirical evidence supporting there ameliorating effects).

I do believe, at least in my eyes, that parts of this experiment supports at
least some of the ideas you have posited in this post.  Thus, this is at
least some direct experimental evidence linking some the concepts of
"supersystem configuration" (a term that I wouldn't mind having you define a
little more clearly) and memory trace consolidation that you advocate.

Also I wouldn't mind reading this "infamous" AoK paper I hear so much about.

Sincerely,

NMF



"k p Collins" <kpaulc@[----------]earthlink.net> wrote in message
news:1JGPb.18521$i4.9300 at newsread1.news.atl.earthlink.net...
> It's a "supersystem configuration" [AoK, Ap6] 'map' -
> an array-processor in which, via the alternating merging
> of specific and non-specific activation, TD E/I(down)
> is converged upon via 'blindly'-automated 'latching'
> that occurs when TD E/I(up) occurs within 'array
> units' ["columns" of hippocampal allocortex], topo-
> graphically-ordered outputs are directed to the thal-
> amus, where "supersystem [system of systems] con-
> figurations" are established.
>
> These TD E/I-minimization dynamics are robustly-
> self-organizing be-cause, if an 'inappropriate' "sup-
> ersystem configuration" is converged upon, the 'in-
> appropriate' behavioral manifestations will induce
> feedback, from the external experiential environ-
> ment, and that will induce TD E/I(up) within the
> hippocampal TD E/I-minimization, and the dyn-
> amics will 'blindly' and automatically converge
> upon a different "supersystem configuration". And
> so forth, all the while, that neural activation which
> just recurs most-often will, through microscopic
> trophic ["growth"] modifications that =only=
> directly reflect the neural activation that actually
> occurs, will be created. These "micro-mods" are
> literally analogous to "mass" as it is invoked in
> Physics, and impart "inertia" within the neural
> activation dynamics that are converged upon
> via TD E/I-minimization.
>
> "Memory" is =distributed= throughout the network,
> at =all= scales from molecular to global-system,
> and is constituted by this "biological mass". All
> the hippocampus does is act as a "traffic cop'
> with respect to that neural activation that re-
> mains after TD E/I-minimization is converged
> upon. 'Memory' occurs within the hippocampus
> in the allocortical version of the 'same' way that it
> occurs within the neocortex. When hippocampal
> function breaks-down, new memories become
> much more difficult to form be-cause the hipp-
> ocampus is no longer governing "supersystem
> configuration" - so the 'switches' don't get
> thrown, robustly, within thalamus. 'Memory'
> can, however, still be generated via round-about
> means [L. Squire long-ago Verified the latter.]
>
> The hippocampal array processor is robustly
> tunable - how to say it? Like one of those
> conformable full-of-'nails' Art-things, where
> one places one's hand on the array of 'nails',
> raises the thing so that 'gravity' rearranges the
> nails so that, when one lowers the thing and
> removes one's hand from it, an 'imprint' of one's
> hand is left in the conformation of the thing's
> arrayed nails.
>
> In the hippocampus, the array-units are finely-
> tunable, not only across the hippocampus, but
> within their columnar structures, in a roughly-
> analogous way, except that, instead of a 3-D-
> smooth 'imprint', it's 'just' TD E/I-minimization,
> as above, that does the tuning.
>
> See AoK, Ap5 for further, necessary, discussion,
> especially with respect to "amygdalar priming".
>
> Please get-beyond the False notion that the
> hippocampus is a 'spatial map'.
>
> There is an =illusion= of it's 'being a spatial map'
> because ['disregarding' the 3rd spatial dimension,
> which makes no sense because that's where the
> tuning occurs within hippocampus] the allocortical
> surface is as a 2-D 'sheet' which is reminiscent of
> a "map", and because folks've cross-correlated
> experimental animals' maze behaviors to hippo-
> campal activation, but that 'correlation' is artifactual,
> because the it's the "supersystem configuration"
> dynamics that are actually determining the animals'
> maze behaviors. The only "space" with which hippo-
> campal function is 'concerned' is the =internal= 3-D
> "supersystem configuration" space, with respect to
> which the hippocampus 'maps' dynamic neural
> interconnectedness.
>
> Get it.
>
> All the verifying refs are cited in AoK.
>
> Please work to understand what's here.
>
> It will stand for all 'time' [or at least until evolutionary
> dynamics alter the neural Topology at a Fundamental
> 'level'.]
>
> It's Gift-stuff.
>
> You know?
>
> Gees, 'louise'! The Children have waited for your
> concurrence long enough!
>
> Get over it.
>
> K. P. Collins
>
>





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