Right visual field to left hemisphere. Why?

kkollins at pop3.concentric.net kkollins at pop3.concentric.net
Tue Oct 13 22:47:21 EST 1998


F. Frank LeFever wrote:

> 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"?

First, I specifically referred to "stimulation" that will result in tissue
damage... noxious stimulation... "pain".To see the point, one must
cross-correlate things a bit, and the best place to start is in an analysis
of the sensory inputs to the cerebellum. The "Rossetta Stone" is the
alternating hemi-deficits to the face and body that accompany lateral
hemisection of the brain stem at the level of the medulla. Pain from the
face is mapped ipsilaterally while pain from the body is mapped
contralaterally. Via the reticular formation, these inputs are made
relatively-scalar... they lose their specificity, while maintaining their
neighborhood geometry, and are conveyed as mapped excitations into the
cerebellum.

Since the outputs of the cerebellum, arising solely from the Purkinje
cells, are totally inhibitory, the outputs of the cerebellum can only form
a "negative image" of the incoming "pain" activation. When this "inverted"
activation is passed, via the deep cerebellar nuclei, back to the
effectors, voi la! The effectors that had been relatively most-activated in
driving the body toward the environmental source of noxious stimulation
become the effectors that are least activated, and the effectors that were
least activated become the effectors that are relatively-most-activated.
Examine this and you'll see that, in it, is a  mechanism that "knows" how
to activate the effectors so that they will move away from environmental
sources of tissue-damaging stimulation, which is an information-processing
problem that's of infinitely-large scope... one which our wonder-filled
nervous systems, never-the-less, resolve in millisecond time frame.
Beautiful, no?

To see it, contemplate the way that the head and body =must= move with
respect to noxious stimulation to the face and body. The head must move
away from pain to the face... lest more tissue damage occur. But, in order
to bring the powerful higher sensory modalities into play in the task of
avoiding noxious stimulation to the body, the head must orient toward the
environmental source of pain to the body. The "curious" mapping of pain
sensation from the face and body, briefly described above, exists solely
for the reasons described above. It can be traced throughout phylogeny...
it's raison detre is always the same as it's described above.

And when you look and see, you'll see that all the nervous system has to do
to resolve this problem having infinitely-large scope is minimize the
topologically-distributed ratios of excitation to inhibition occuring in
this neural architecture. It's "just" so Beautiful!

> And why do you imply that "stimulation" is to be avoided?

I referred specifically to tissue-damaging stimulation. Avoid such to
minimize tissue damage.

But that's not the end of things. The Pain architectrue, briefly outlined
above, is a "door", thrust open wide, through which an integrated
understanding of the functioning of every nuclear group within the nervous
system can be attained.

>>How would it cause "damage" if not decussated?

The survival-advantage goes to minimized latencies, minimal circuit
lengths, etc. The architecture outlined above is such.

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??

First, although there exist "counter examples" (the best I've come across
is the tree shrew), I disagree with you on the proposed "evolutionary
trend". The trend is only in the direction of enhancement of the same
neural-architectural "theme". The ipsilateral optic routes are, in fact,
"just" more of the same. So is the ipsilateral medial architecture.
Remember, the outputs of the eyes must be mapped optimally with respect to
the task of avoiding tissue-damaging stimulation if an organism is to "win"
a survival contest with a competitor. Least latencies, shortest pathways,
coincide with such... can't have the part of the visual field that's
correlated with "left" be mapped in any way other than to the left if the
organism is to have a chance to survive conflicts with competitors in its
evolutionary niche.

> (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?

the general information-processing problem... how to assure that the
activation that occurs at any locus can be "comprehended" within the
activation that occurs at all other loci.

>  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--

Not only that... it goes on and on. For instance, while preserving
everything that I've discussed so far, the primary sensory and motor
cortices are "mirror-images". This is architecture that facilitates
learning through experience via a the same TD E/I-minimization dynamics
that were described above. Sensory activation drives the formation of
"templates". Subsequently, when the global system enters into a
motor-dominant "state", the mirror-image sensory templates permit that
which was formerly experienced afferently to be replicated via simple TD
E/I-minimization. (Sadly, because this has not been generally comprehended,
a Child that is battered will tend to automatically acquire battering
behaviors... the sensory experience of being struck is automatically
transformed into its geometrical mirror-image... striking.)

   >so that it coincides

> >exquisitely with the lower-level prerequisite
>
> -mapped onto a PREREQUISITE?!?  Now you've lost me.

Have I cleared things up with what's posted here? It's simple.
Tissue-damaging stimulation must be avoided. An organism lives out its
alloted lifetime only to the degree that it avoids tissue damage (' course,
its gotta eat, too :-)

>  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...

In =every= sense of the word.

>  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?

My use of "hand-shaking" was just a euphemism for "global preservation of
the topological mapping"

>  All of
> >this can be taken all the way down to the molecular level,
>
> Now you're pulling my leg!

Nope. It's already worked out.

>  (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?)

1980.

> I have a sinking feeling: might the author be "ken" ???

I confess.

> (hope its not a nom de plume for kccheng...)

Now you've lost =me=.

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

Cheers, Sir. ken collins




More information about the Neur-sci mailing list