X-Message-Number: 8041
Date:  Thu, 10 Apr 97 21:55:11 
From: Mike Perry <>
Subject: Seat of Consciousness

In an earlier post today, I made an effort at defining the "seat of 
consciousness." I said it was the minimal brain region, some part of 
which is always active when the subject is "conscious." But this 
definition has problems, and won't always work. For example, 
suppose the whole brain is needed for consciousness, i.e. every 
neuron must be active or you have no consciousness. Then every cell 
could qualify as a "seat of consciousness" as I've defined it--there 
would be no single seat of consciousness.

In practice we might aim at an  "operational" definition. If, using 
PET scans, etc. we find that some part of the brain is always 
active when consciousness is present, is sufficient by itself for 
consciousness, and no other part of the brain meets either of these 
two requirements, we could identify that part as the seat of 
consciousness. 

But it's also interesting to pursue the more theoretical problem a 
little further. (This perhaps would offer additional insight into 
both natural and artificial systems that might qualify as "conscious" 
to some degree.) So I propose the following. First, say we call a
part of the brain that is required for consciousness a primary 
region. This means that if this part is shut down completely, there 
is no consciousness. So the whole brain in particular is one 
such region. (Here I'm assuming that consciousness--the consciousness 
of "the person who speaks" anyway, is resident somewhere in the 
brain. Another assumption is that the smallest functioning subunit of 
the brain is a cell, so that all regions brain are finite sets of cells.)
It ought to be possible then to talk about a minimal primary 
region--a region of the brain as small as possible, that is required 
for consciousness. Of course, in the real, fuzzy world the 
applicability of this concept cannot be taken for granted either, but I'm
assuming it here as a "first cut." Every primary region, then, must 
have at least one minimal, primary subregion, given that 
we can go all the way down to the level of individual cells as
our subregions. I would then define the seat of consciousness
as the union or sum of all the minimal primary regions.

For example, let's assume that the whole brain had to be active to 
have consciousness--turn even one cell off and you lose it (very 
unrealistic, but useful for illustration). Then the minimal primary
regions would consist of a single cell each, and 
their sum would be the whole brain as required. On the other hand,
if the MTRF, fully active, were both necessary and sufficient for
consciousness, then again the minimal primary regions would be
single cells--in this case cells of the MTRF--and their
sum would be the whole MTRF. If there are two, disjoint
regions of the brain, each of which could independently support
consciousness, but at least one had to be completely active, then
the minimal primary regions would consist of a *pair*
of cells, one cell chosen from each region. The seat of consciousness
would then be the sum of the pairs, i.e. the sum of the two regions.
Similarly, if there are n disjoint regions, such that turnon of one is both 
necessary and sufficient for consciousness, then the minimal 
primary regions would consist of (unordered) n-tuples of cells, each
cell chosen from one of the n regions, and the sum of the n regions
would again be the seat of consciousness.

The above examples are vastly oversimplified from real life, of 
course, but will convey the general idea. I think this idea bears 
further investigation (or quite possibly it has been investigated).
With a little more mathematical rigor, it might be made into a theory
that would produce interesting theorems--then we would have to
see how far the results might be relevant. Or perhaps there are
still major flaws in this approach, that investigation could uncover
and correct.

Mike Perry

http://www.alcor.org

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