Right visual field to left hemisphere. Why?

F. Frank LeFever flefever at ix.netcom.com
Tue Oct 13 21:03:43 EST 1998


In <3622AA2B.54FFF0A4 at pop3.concentric.net> kkollins at pop3.concentric.net
writes: 
>
- - - - - - - - -(snip) - - - - - - - - - - - - - - -

>  The tree shrew is wired up in the fairly-primitive way that's been
>discussed. In most mammals, the neural-fiber crossings
("decussations")
>occur for a reason that's a tad more-complex. The most-basic, and
>relatively-licalized, problem is to avoid "stimulation" that causes
tissue
>damage, and decussation handles that mightily.

Now you've lost me.  How does decussation avoid "stimulation"?  
And why do you imply that "stimulation" is to be avoided?
How would it cause "damage" if not decussated?  Given that there may be
an evolutionary trend towards LESS complete decussation (a large
proportion of human optic input is IPSILATERAL, i.e. NOT DECUSSATED),
are we therby more damaged than your average pigeon??

(incidentally, Gazzaniga is speaking at NYU Center for Neural Science
at 12:00 noon next Monday...)

Naively, I assume that decussation sends signals from left somatic
stimulation to "stimulate" the right forebrain, and from right somatic
stimulation to the left forebrain--each hemisphere thereby being
"stimulated".  I have always thought that "stimulation" was the natural
function of afferent activity, unless you have some special definition
of "stimulation".



 At higher-levels (cognitive)
>the problem

Which problem?


 is transformed into a global-integration problem. Not only the
>visual system, but =all= systems are topologically (geometry with
twists and
>turns and area stretchings or shrinkings) alligned so that
>neural-impulse-bourne information is always mapped

Yes, yes, I THINK I follow you: the several sysems of EACH modality
(somatosensory, visual, etc.) are roughly topologically arranged,
preserving somewhat the spatial relationships of their peripheral
origins, as they are mapped onto--


 so that it coincides
>exquisitely with the lower-level prerequisite


-mapped onto a PREREQUISITE?!?  Now you've lost me.


 of avoiding "stimulation" that
>damages body tissue.

Well, yes, we ALL want to avoid stimulation that damages body tissue;
that goes double for Mother Nature!  But how does topographical mapping
and/or. decussation avoid THAT???


> Consciousness is enabled in this way...

In what way?  by twisting and turning but preserving decussaition and
topographical orientation??? (or is it topological?) (sorry)


 every part of
>the nervous system "comprehends" what's going on in every other part
of the
>nervous system

Well, MAYBE, but not in any normal sense of the word "comprehend",
given the many dissociations one can find even in normal cognition...


 because of this exquisite topological "hand-shaking".

WAIT A MINUTE--how do you get from topological mapping and decussation
to "hand-shaking"?  What does one have to do with the other?


 All of
>this can be taken all the way down to the molecular level,

Now you're pulling my leg!  (Let's hope it doesn't cause too much
stimulation or damage)


 and it all stands
>proven (and has for more than a decade). ken

Can you be more precise in your citation of the proof?  If not the
actual volume number and page, perhaps the name of the author and/or
journal and at least a hint at the year?  (more than a decade...maybe
l987? 1986?)

I have a sinking feeling: might the author be "ken" ???
(hope its not a nom de plume for kccheng...)

F. Frank LeFever, Ph.D.
New York Neuropsychology Group




>




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