[long, off topic info] decussation problem

kenneth paul collins KPCollins at postoffice.worldnet.att.net
Thu Oct 31 23:34:49 EST 1996


miandan at geocities.com wrote:
> 
> > The phenomenon of decussation constitutes a portion of an
> > elegant solution to the the infinitely-large problem of
> > activating the effectors so that the body will move away
> > from environmental sources of noxious stimulation.
> 
> Decussation has nothing to do with that.  It absolutely
> does not matter which side of the brain sends the command
> to move away from a noxious stimulus.

I'm telling you, it does. How it's so is disclosed following 
hemisection of the brain stem at the level of the medula. Pain & 
temperature sensation are lost on the same side of the face and on 
the opposite side of the body. This occurs because the ipsilateral 
spinal trigeminal tract, and the contralateral spinothalamic tract 
are severed. 

The correlation with necessary movement is that while the head 
must "move away from" environmental sources of noxious stimulation 
to the face (to avoid further tissue damage), it's useful for the 
head to orient toward environmental sources of noxious stimulation 
to the body (so that the powerful visual and auditory systems 
enter into the determination of avoidance behavior).

The correlation with the neuroanatomy is that both the 
spinaltrigeminal & spinothalamic tracts project collaterals to 
reticular nuclei which project ipsilaterally to the cerebellum. 
The activation that follows this route conveys pain's "mountain". 
The outputs of the cerebellum are entirely-inhibitory, so they 
take the "mountain" and transform it into a "valley", and project 
this "valley" back to the effectors via the deep cerebellar 
nuclei.

Now, this could be accomplished without the great decussations, 
but the result would be significantly less-powerful because fiber 
lengths would be increased, and therefore activation latencies, 
and therefore, survival propensity would be decreased relative to 
organisms having the crossed neural topology.

This pain-avoidance architecture permeates the CNS at all levels.

> 
> > When one studies the neural architecture of decussation, one
> > finds that it enables the nervous system to activate the
> > effectors "appropriately" by simply minimizing the
> > topologically-distributed ratios of excitation to inhibition
> > that are occuring within the nervous system.
> 
> I do not understand what you are trying to say.  What is
> "a topologically-distributed ratio", and how can it be
> minimized by decussation?

It's necessary to use the "topologically-distributed" modifier in 
 order to address the twists, turns, and crossings of the fiber 
pathways. "Topographical" does not connote such. Decussation 
constitutes the structural order that aligns the neural 
"neighborhoods", preserving their topographical correlations, so 
that the necessary inversion of inputs and outputs (the 
"mountain"-"valley" transformation) will occur. The minimization 
occurs because the reticular excitation breeds cerebellar 
inhibition. (Using the "ratio" is just a compact way of saying 
excitation is minimized and inhibition is maximized.)

> > That is, the neural architecture receives pain-stimulation
> > "mountains", inverts them into neural-activation "valleys",
> > and sends this "valley" activation back to the effectors,
> > where the "valley" activation is "just the ticket" to the
> > body's "moving away from" the environmental source of
> > noxious stimulation.
> 
> May be, may be, but this has nothing to do with the decussation.

I'm sorry, it has everything to do with decussation. Decussation 
is =required= if neighborhood relationships are to be perserved 
while fiber lengths, and hence activation latencies, are 
minimized.

> > This all works because everything within the CNS is
> > rigorously mapped with respect to the body-environment
> > interface.
> 
> Everything within the CNS may be mapped, but mapping is possible
> without decussation.

but, as is explained above, a crossed will outperform an 
otherwise-equivalent non-crossed system.

> > And it all reduces directly to what's described
> > by the 2nd Law of Thermodynamics (WDB2T). ken collins
> 
> Clarify.  I do not understand what you mean.

The correlation between decussation and what's described by the 
2nd Law of Thermodynamics (WDB2T) is huge, but consider only the 
shortening of fiber lengths that decussation makes possible. Not 
only does this shorten activation latencies, it also 
lowers energy consumption, thus increasing the efficiency of the 
system's performance.

> > People hate because they fear,
> 
> Probably correct.

It is.

> > and they fear because
> > they do not understand,
> 
> What do you mean?  A rabbit does not understand that it may
> be eaten by a wolf?

It means, simply, that because this or that is unfamiliar, when it 
is encountered, it constitutes a stimulus set that will cause TD 
E/I to become elevated. All our nervous systems know innately is 
that, just as was the case in the pain-reactivity described above, 
TD E/I(down) is "good" and TD E/I(up) is "bad". As we experience 
stuff, our nervous systems are continually "whittling" away 
unnecessary neural activation - "striving" to achieve TD 
E/I(min) - with respect to it. As TD E/I(min) is approached, the 
correlated elements of the environment acquire the quality of 
"being familiar". It is =this= that constitutes "understanding".

Folks fear because they experience TD E/I(up) (because they do not 
"understand").

> > and they do not understand
> > because hating is less work than understanding.
> 
> Hating may be a lot of work.

I'm addressing the ubiquitous short-term tendency to "move away 
from" that which elevates TD E/I. I agree with you. The short-term 
expediency is the long-term arduousness. By not doing the work 
necessary to =really= educate the Children, Society condemns 
itself to having to do vastly-more work "corralling" the adult 
predators that were born of the former "expediency"... I agree, 
hating =is= a lot of work. It's just that, over the short term, 
"moving away from" is the "easiest" way to achieve TD E/I 
minimization. (The overal behavior reflects the same "fundamental 
wisdom" as does the pain reactivity discussed above. That's why I 
use the term "moving away from"... to address the same-stuff 
nature of all CNS function... it's all "moving away from" TD 
E/I(up), and "moving toward" TD E/I(down)... blindly.

The understanding that's being discussed removes the "blindness". 

ken collins
_____________________________________________________
People hate because they fear, and they fear because
they do not understand, and they do not understand 
because hating is less work than understanding.



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