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brain plasticity - what causes it?

ken collins kckpaulc at aol.comABCXYZ
Fri Nov 5 21:17:29 EST 1999


>Subject: brain plasticity - what causes it?
>From: jander at unf.edu  (John E Anderson)
>Date: Fri, 05 November 1999 02:49 PM EST
>Message-id: <382332F5.A9BCFE3A at unf.edu>
>
>Hi all
>
>I would like to tap into the collective wisdom of the list in hopes of
>answering the following question:
>
>Does any kind of neuronal activity in the brain induce plasticity, or is
>plasticity induced only by certain kinds of activity?  In other words,
>do changes in brain tissue -- either through modification of synapse
>strengths, establishment of new synapses, or some other route -- become
>more likely in response to action potentials in *any* kind of neuron, or
>does the activity have to be in a special kind(s) of neuron?
>
>Thanks for any help you can provide.  I would especially appreciate
>pointers to relevant papers or other sources of information.

hi, John.

there's no 'easy' answer to your Q because, depending upon developmental
'stage', degrees, and forms, of 'plasticity' vary.

in early development (including prenatal), everything's 'plastic', and
activation-dependent (which is not the 'accepted' view, but which can be
readily verified through the study of =existing= experimental data, such as
frog tectum transplant).

it's my view that the nervous system, =as a whole=, remains 'plastic'
throughout life, but that, since in 'areas' such as the spinal cord, avtivation
is relatively-highly-stereotypically-repetitive, the existing plasticity 'just'
continues to converge in the stereotypical way. this's why, BTW, early training
yields outsized performance benefits (developmental plasticity is nonlinear,
because of the stereotypical-activation-mitigated convergence (which is 'just'
another window into TD E/I-minimization), which is one of the things that's
discussed, with respect to higher-'level' neural information-processing, in
AoK, Ap7, with respect to volition (the 'volitional diminishing-returns
decision')). in the beginning =everything= is astereotypical, but as experience
is acquired, convergence upon stereotypy augments (again, via TD
E/I-minimization (that such is not a 'prison' is among AoK's main 'points'))

anyway, the low-'level' plasticity is robustly-testable experimentally (as long
as enough organic stuff remains, post-lesion), and actually stands verified,
sans lesioning (myographically, or via 'just' plain ol' observation), in
examples from the training of athletes... 'practice makes perfect' is the same
as saying 'plasticity continues' even at spinal 'levels'.

it's the same throughout the CNS, but higher-'level' 'areas' remain
relatively-more-plastic be-cause their 'normal' activation is relatively-more
subjected to the stochastic (having a random component) activation of the
'Reticular System' (AoK, Ap3, Ap5), which tends to prevent things from
'falling' into stereotypy... be-cause of such, there's always the opportunity
to converge (achieve TD E/I-minimization) in novel ways... hence the
more-robust 'plasticity' that occurs at higher-'levels' within the neuraxis.

even the genetic unfolding of the nervous system is activation-dependent...
that is, within a range that's delimited by the necessity to optimize overall
nervous system information-processing dynamics re. survival, 'plastic'...
studies of environmental adaptations disclosed such long ago... just wasn't
recognized for what it is... thus, when one takes things all the way down, one
sees that even the DNA is 'plastic' in an
intergenerationally-activity-dependent way, be-cause if progenitors do not
pursue this or that pro-adaptive behavior, it doesn't matter what happens at
the 'level' of the DNA, because the environmental 'stress' will exceed the
degree to which the DNA can modify, successfully yielding a new starting
'blueprint'.

there was an interesting article, in the recent past, about this very sort of
thing in _Science News_ (i've already put the issue in my plastic thing (no pun
intended), but will look it up and post the ref (might be on the _SN_ web
site))... had to do with ground squirrels' taunting of snakes... the DNA
plasticity is readily-observable.

despite all the arguments that rage over what 'memory' is, and how it happens,
it's all 'just' activation-dependent TD E/I-minimization... overall, that which
cannot adapt within the nervous system diminishes survival propensity... so
everything in-there is, to varying degrees (as above), 'plastic'.

it's just that there is a 'ball-park' design that happens to be imbued with
extremely-very-extraordinary information-processing capacities, so nervous
systems tend to stay within this 'ball-park'.

one just has to get the big picture before the everywhere-'plasticity' becomes
'visible' to thought.

cheers, ken (K. P. Collins)






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