left-right reversal of CNS: Why?

kenneth paul collins KPCollins at postoffice.worldnet.att.net
Mon Sep 9 16:40:45 EST 1996


>Nor do I really know why there is crossed representation

decussation exists within all mammalian nervous systems...

>I don't know if the crossed image on the retina has anything to do with
>it.  After all, the lens also reverses things up-down as well as
>left-right.

yes, and the primary sensory & motor maps are also left-rignt reversed 
and up-doen inverted... in complete agreement with the mapping of the 
retina into the lateral geniculi and, from there, onto the primary 
visual cortex... throughout the whole route, although there are some 
"adjusting" features (most-interestingly, the "fanning-out of the tract 
as it travels between the lateral genictli and the vcx... which 
implements "timing" appropriately with respect to the 
necessarily-spread-out cortex), this globally-relavant topology is 
maintained...

>Anyway, contralateral representation works differently in
>the visual system.  The somatomotor and somatosensory pathways cross to
>the opposite side of the body, at the level of the medulla.  The visual
>pathways cross, not from one eye to the contra hemisphere, but from the
>left visual field of EACH eye to the right visual cortex and vice
>versa.

the purpose of this topology is to allign each visual hemifield with 
each primary hemi-somatosensory and primary hemi-motor map that are all 
that exist in each cerebral hemi-sphere...

>This is good, because if you lose one eye you don't lose half of space!

...this follows from what's outlined above

>The result is also that the left side of the brain works the
>right arm and sees the right visual field, which seems convenient-- but
>I don't see why it wouldn't work just as well with ipsi representation.

it's exactly for this reason that I extend the analysis back to 
organisms having radial (ipsi-"lateral"-radially) symmetry... a modern 
version of such evolutionarily-old symmetry does, in fact, exist within 
mammalian nervous systems... in my work I refer to such as the 
"protopathic system" (or the "reticular system")... encludes the 
reticular formation, intralaminar thalamic nuclei, substantia gelatinosa 
redion of the spinal column, etc... it's topology reflects that of the 
radially-symmetric organisms...

...the "inside-out" nature of the crossed system (the "epicritic system" 
in my work) developed on top of the protophthic architecture, and 
functions to lift things above the jelly-fish's 
slow-motion-difficulties... the crossed neural architecture minimizes 
conduction latencies =globally=... such is highly-conducive to survival 
within an environment in which there's competition for food, 
procreation, etc...



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