brain and mind

Gordon Kendall Gray gord at homostudy.win-uk.net
Tue Apr 18 17:16:36 EST 1995


reply to gord at homostudy.win-uk.net

  In article <68706.caudle at irp.nidr.nih.gov>,
(caudle at irp.nidr.nih.gov) writes: 
>On 23 Jan 1995 23:11:08 -0500, 
>Thomas R. Gregg  <greggt at strauss.udel.edu> wrote:
>> <jwwilliams at gems.vcu.edu> wrote:
>>>Those of us who deal with the brain and thought are at the same impass.  We 
>>>cannot explain how its working using 16th century physics.  The paradigm must 
>>>change but science need not be abandon.
>>>>Can we agree that the brain is an information processer and
that thought is the form taken by the processing? 
        This brings us to the next question about the form taken by
the information being processed - Is it analog or is it digital?
Subsidiary question - how can we decide this when the information
is carried by pulses (please note the plural!) In a digital
computer the pulses are arranged to appear at precisely defined
times from which they cannot be allowed to depart, but at those
times they can be present or absent. Coincidence detectors (known
to computer engineers as NAND and NOR circuits) detect pairs of
pulses occurring simultaneously - in a brain the same principle
operates in lateral inhibition and the circuits are very much like
NAND and NOR in structure.
        I had to mention this because the similarity of the
circuits is irrelevant to the analog vs. digital issue and causes
serious confusion - what is crucial concerns the timing between
pulses - the pulse recurrence frequency (PRF).  The raw information
coming from receptors takes the form of continuously variable PRFs,
unlike the rigidly defined ones in your computers, where the
position of the pulse in time or space has numerical significance
as powers of 2. The form of information in the brain is therefore
by definition analog information and it has to be carried through
in that form to the effectors that are being brought into play.
There is no analogue-to-digital-to-analogue conversion system -
what elaborate form of natural selection could produce it? Genetic
engineering might produce it but that is a very long way off.
Meanwhile, one might ask "Is it worth the effort involved?"
        The fact that a brain is an analog information
processer is profoundly important when we consider its potential
flexibility as compared to that of the most powerful PC or a Cray:
- Because it is dealing with a continuously variable form of
information, it has the potential of assuming at any single
instant, any one out of an infinite variety of configurations,
unlike the digital computer whose range of possible configurations
is limited by the number of bits the hardware can hold. This much
is true of even the simplest brains.  It is therefore pointless to
speculate about "bits", "bytes" or "megabytes" in a brain since it
doesn't use them.
        Does someone ask "What about Memory?"? In all probability
someone does, and certainly it should be asked because its
existence is a material fact that needs to be understood
and explained. The number of cells that can be involved directly in
the act of remembering in any brain is most certainly finite, not
infinite. The underlying question is - How can a finite number of
cells activate an infinite range of information states?
        Any answer to this must take into account the difference
between the way in which the cells of a body remain stable in
relation to their environment and the stability of the
memory components in a computer. Magnetic recording is the most
stable form used in computers, but capacity recording, which must
be replenished at regular intervals, is used in the RAM.
Continuous replenishment is the principle operating in long-term
memory in the brain but the construction of short-term memories
may begin with capacity recording in oligodendrocytal myelin (See
"Memory in Myelin" Gray, Coppock and Gray, 1994). 
        Continuously variable replenishment rates, which affect PRFs
in axons, therefore can cause memories to break through to
consciousness by means of phase discrimination similar to aural
detection of sound-source positions. These are active memories -
the only ones we can ever know and are subject to the same
continuous variability as are the direct perceptions coming
through the receptors. Reminiscences are always being triggered by
more objective experiences of the moment because they are
super-impositions on pulse-trains.
        The continual and continuously variable replenishment of
every cell and its components in the body is what makes even memory
as it is in the brain continuously variable, therefore taking the
form of analog information.

                Gordon K. Gray






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