X-Message-Number: 11420
From: Thomas Donaldson <>
Subject: thanks to Jan Coetzee; much more is known about brains, too
Date: Tue, 16 Mar 1999 23:57:44 +1100 (EST)

Hi everyone!

We should thank Jan Coetzee for his report of one side of the issue of
brain repair. It's important here to understand that now, in animals such
as cats, experiments are going on aimed at replacing neurons lacking
because of earlier brain damage. Moreover, by now it's well recognized
that brain areas which deal with visual recognition generally respond to
several different classes of visual stimuli, rather than just one kind:
yes, some neurons are particularly sensitive, for instance, to horizontal
structures, but that does not imply that horizontal structures are the
only visual phenomena to which they are particularly sensitive.

In general terms it's been known for a long time that information is
widely distributed in our brain. Since, after all, our brains are parallel
machines (with far more processors than any present parallel computer ---
the processors are neurons, in case you haven't guessed) it's very likely
that information will be widely distributed. The earliest experiments 
suggesting this (which also seemed to negate the idea that brain
regions were specialized --- which later was still found to be true)
consisted of systematic ablation of particular brain areas in rats.
Despite this, the rats could still limp or roll through a maze. The
article reported by Jan Coetzee adds to the force of these early
experiments. Yes, our neurons do specialize, but not on one task only...
and they also retain information needed for other tasks (just how I do not
know ... and suspect that no one else does, either, but one possibility 
would be the continued existence of "silent" connections between neurons).

The real problem is that of obtaining this information so that new neurons
introduced for brain repair will grow the proper connections and so 
respond to that previous information. This may turn out to be easy in some
cases, but it seems to me unlikely that it will be easy in all ... or even
in most cases. I will add, though, that many of our neurons play no direct
role in storage of information, and repairing or replacing those neurons
will still have lots of value. Neurons using dopamine as their
transmitter, for instance, play a large role in organizing our emotions
and our knowledge but play little direct role in information storage.

For those who are interested, I have compiled a list of books and papers
on how brains work and just what is now being done in brain repair. I
can email it to individuals who ask for it. I am also well aware that some
people believe that we will someday simply be read off into computers; I
will point out here that in order for such read-offs to be successful, we
will need much more understanding of how our brains work than we presently
have ... even though the last 20 years have seen a big increase in our
understanding. So knowledge of just how our brains work remains highly
relevant even to those who might prefer to live in computers.

			Best and long long life to all,


				Thomas Donaldson
				

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=11420