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From: throopw@rtp47.UUCP (Wayne Throop)
Newsgroups: net.sci
Subject: Re: unused brain capacity
Message-ID: <86@rtp47.UUCP>
Date: Tue, 9-Jul-85 20:27:16 EDT
Article-I.D.: rtp47.86
Posted: Tue Jul  9 20:27:16 1985
Date-Received: Fri, 12-Jul-85 04:25:46 EDT
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Organization: Data General, RTP, NC
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I'd like to expand a little on Stanley Friessen's notes in this thread
of discussion.  For those who tuned in late, the folk knowlege that "we
only use  percent of our brain power" is questioned.  The fact
that some patients with known brain damage are nevertheless able to
think and behave normally is used as a support for this thesis.
Stanley's reply:

> 	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.

And Sandip Chakra's reply to this:

> 	This does not exclude the fact that they were able to do
> above average level work with a few percent of their brain cells.
> Suppose all of us were born with 95% of our brain cells damaged, then
> since we would be working at an above average level anyway, how do we
> know that we needed the other 95% of our brain cells ?

Lacking a complete knowlege of what brain structure is "good for", both
"sides" of this discussion are mostly speculation.  However, I suspect
that the folks who claim that "we only use  percent of our
brain" are incorrect.  I have (essentially) two reasons.

First, the patients on the referenced Nova episode showed that with
about (as I recall) 80% brain damage, they could perform quite
normally.  However, the metabolism of the remaining brain tissue was
quite a bit higher than normal, suggesting that (perhaps) more of the
"essential stuff" was crowded into the remaining 20% of surviving
tissue.

Second, redundancy is not "wasted" capacity.  Let us assume that a
computer has 9 bits to support each 8-bit byte of memory, the "extra"
bit being used for error correction.  Is the computer "wasting" 1/9th
of it's memory?  Not at all.  Or consider a computer that is triply
redundant, or has triply mirrored disk storage.  Is it "wasting" 2/3rds
of it's capacity?  Again, not at all.  I think that a similar effect
applies to the brain.  To be as reliable as it is, it probably is highly
redundant.  Redundancy is hardly "wasted"... it increases reliablity.

Thus a "normal" person who suffers brain damage *can* continue to
perform at the previous level of competence.  This normally does not
happen to adults who have already "parceled out" functions to particular
bits of grey matter, but it *can* happen even to adults.  It more often
happens that children (the examples from Nova were all damaged in early
childhood, for example) can re-allocate brain function after damage and
have few or no perceivable side effects.  Nevertheless, they are far
more susceptible than normal adults to further damage.

To summarize:
- The Tomographic results cited in Nova do not unambiguously show that
  "brain capacity" was destroyed along with brain tissue.  (This is
  essentially a restatement of what Stanley said).
- Even if there is *redundant* brain capacity, it can hardly be said to
  be *wasted* brain capacity.  And, getting back to the original
  question (how would excess or wasted capacity be selected for),
  *redundancy* is a valuable survival trait.
-- 
Wayne Throop at Data General, RTP, NC
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