left-right reversal of CNS: Why?

kenneth paul collins KPCollins at postoffice.worldnet.att.net
Mon Sep 9 16:52:28 EST 1996


>btw, most cranial nerves have either ipsilateral or bilateral
>representation.

this neural topology occurs because the motion problem, with respect to 
the head, differs from that of the body...

if the medulary brainstem is hemisceted laterally, there will be a loss 
of pain and temperature sensation on the same side of the face as the 
lesion, but on the opposite side of the body...

...now think... if one is walking in the woods at night, and something 
pokes one in the face, how should one's head move? ...away from the 
poking thing... but if something pokes one in a leg, it's very-helpful 
in organizing one's avoidance behavior if one's head orients toward the 
enviornmental source of the noxious stimulation... (the practical joke 
which has one duped into looking at some point on one's body, only to 
run into a (hopefully, gentle) finger to the face "hinges" upon the 
function that's being discussed...

...this neural topology is as it is so that the sensory innervation will 
be alligned with the totally-inhibitory outputs of the cerebellum (which 
arise from the cerebellar purkinje cells), and allows the 
infinitely-large avoidance problem to be resolved in millisecond time 
frame by "simply" minimizing the topologically-distributed ratios of 
excitation to inhibition (TD E/I) involved...

...decussation occurs so that this one information-processing dynamic 
will be optimized...



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