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From: stpeters@steinmetz.UUCP (R L StPeters)
Newsgroups: net.sci
Subject: Re: Re: darwinism
Message-ID: <169@steinmetz.UUCP>
Date: Tue, 9-Jul-85 23:06:41 EDT
Article-I.D.: steinmet.169
Posted: Tue Jul  9 23:06:41 1985
Date-Received: Sat, 13-Jul-85 14:15:07 EDT
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> >I don't know about the % of gray matter "normally" used, but ...
> >
> >Using recently developed (tomographic?) techniques for scanning
> >the brain in detail along various physical variables, researchers
> >found that a number of people who suffered massive brain damage
> >at birth or early in life but who display not only above average
> >abilities but high general intelligence (unlike the "calculating
> >idiots") are using less than 10%, in some cases less than 5%,
> >of their brain mass: the rest is clinically or effectively dead!
> >
> >I haven't though about how this relates to evolutionary issues,
> >but it struck me that these simple facts must have a serious
> >impact on various theories about how the brain works: ...
> >
> 	Actually, before any conclusions can be drawn more details
> are needed. What proportion of the dead tissue was gray matter and what
> white? How much was glial cells and how much neurons? What about the
> density of neurons in the remaining tissue - the same or perhaps
> higher? What sections of the brain were involved? Of course the
> answers to some of these questions requires a biopsy or similar
> invasive sampling technique, so we may have to wait until some of
> these patients die. Also, why were they given a tomography(a
> diagnostic test) if they were so normal?

The patient's death is not all that necessary.  My neurosurgeon and
my tomographic pictures can both attest that a sizeable region of
my own brain has not held working neurons since I had a significant
subarrachnoid hemorrhage and subsequent open-brain surgery not quite
a decade ago.  I have had the enlightening opportunity to observe
up close the nearly-complete restoration of lost functionality as
the initial total paralysis of my left arm and hand have gradually
given way to the point where I am touch-typing this posting (sneaking
in an occasional peak at the keyboard).

While the damage I suffered was nothing approaching 90% overall, it
was 100% throughout a region large enough to make some impressive
tomographic images.  Given that central nervous system neurons do
not recover or regenerate, this functionality must be being supplied
by other neurons, presumably in the vicinity of the destroyed region,
and also presumably neurons that were not already otherwise in use.
(At least I like to think so.)

This leads me to the conclusion that, however evolution has managed
to do so, it has put all these extra unused neurons in there in the
first place as spare parts.

Recoveries of major losses of functionality that take a decade to
occur are unlikely to have much evolutionary benefit, so they most
likely are a side benefit of a mechanism whose purpose is continual
maintenance: ongoing repair of minor damage.  The image I have is
one of steady loss of active neurons due to disease, chemicals (e.g.
alcohol), physical blows to the head, etc., accompanied by their
continuous functional replacement through activation of alternate
neural channels using these pre-existing replacement neurons.

Thus nature, faced with only one chance ever to grow neurons, grows
enough initially to provide a lifetime of spares.  More precisely,
an adequate *density* of spares is provided.  The numbers seem to
suggest that perhaps around ten possible replacements are provided
for each neuron.

Carrying this one step further, one can then imagine that perhaps
a part of the condition we call senility is when the loss of neurons
from old age requires that the brain reach ever farther to find
suitable neural replacements, and the neural pathways, like old code
patched many times, become ever more tangled and spaghetti-like.

While I described the hypothetical repair process in one-for-one
neural replacements terms, I doubt the replacement of neural pathways
is that simple.

I've progressed from some observations and a few known facts into
some pretty tenuous conjecture, and it's time I stopped.

-- 
R. L. St.Peters (Dick)        The "R" is for "Reptile".
uucp: decvax!mcnc!ncsu!uvacs!edison!steinmetz!stpeters (uucp is forever)
arpa: stpeters@ge-crd                                  (federal express)
	"Any opinions expressed by my employer are probably not mine."