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Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!cbosgd!rbg
From: rbg@cbosgd.UUCP (Richard Goldschmidt)
Newsgroups: net.ai,net.philosophy,net.rumor,net.misc,net.junk
Subject: Re: A Quick Question - Mind and Brain
Message-ID: <20@cbosgd.UUCP>
Date: Thu, 14-Jun-84 10:29:14 EDT
Article-I.D.: cbosgd.20
Posted: Thu Jun 14 10:29:14 1984
Date-Received: Fri, 15-Jun-84 01:00:02 EDT
References: <186@isrnix.UUCP> <3588@fortune.UUCP>
Organization: AT&T Bell Laboratories, Columbus
Lines: 69


> I believe there are aprroximately 10 to the 9th neurons in a human
> brain, if that's of any help.  Add in the glial cells (there is some 
> debate about their function) and it comes to 10 to the 10th.  
>  Bob Binstock

Those numbers are both wrong, but so was the number in my original posting.
Let me correct the numbers, and add the discussion to some other groups which
may or may not be interested.

Recent estimates of the number of neurons in the human brain have been
increasing, for a current estimated total of between 30x10^9 and 50x10^9.
Glial cells outnumber neurons by at least 10 to one, and occupy about half
the volume of the brain, but the ratio varies widely between brain regions,
and between species within a brain region.

To get an estimate of the computational equivalent of the brain:

Assume 5x10^10 neurons with 2x10^4 synapses each = 10^15 synapses/brain.
Each synapse, on average, adds in a quantity about 20 times/sec (it can
go much faster, but not many do at the same time).  So that's 2x10^16 very
simple approximate adds per second.

Even when everything is just right, a Cray can't do better than about 10^9
simple integer adds per sec.
So, IF THE SYNAPSES ARE BEING USED WITH TOTAL EFFICIENCY FOR PERFORMING
THE TASK, a brain is worth about 10^7 Crays.  

[Credit for this calculation to Terry Sejnowski (Biophysics, Johns Hopkins)
and Geoff Hinton (Computer Science, Carnegie-Mellon)].

It is not surprising that most tasks use only a small fraction of this
capacity.  However, I think the computation of the amount of information
used to store sensory perceptions by hound!rfg may be misleading:

>>if I assume a visual field as 10**3 bits high by 10**4 bits wide
>>by 10 bits for color and shading of each element, we have 10**8 bits
>>per visual field. Suppose a life time of 72 years and 16 hours a day of 
>>observing (neglecting "visual dreams" which may also be remembered),
>>with a new observation every 10 seconds. I multiply it all out to
>>about 1.5 x 10**16 bits. (187,500 billion bytes?)
>>Adding audio, tactile, olfactory, taste to that ought to easily run the
>>total over 200 gigabytes. That's just for remembering observations
>>(eidetically, which is a faculty some do have). 

Most people do not remember every detail of every scene they ever see.
How much of your early childhood (0-4) do you even remember at all?
Emotional content of a situation can have a large impact on what and how
much you recall.  Dangerous or joyful experiences stand out in memory
more than most neutral events.

The role of language is also an important issue in considering the storage
and information processing capacity of the brain.  Using a word to stand
for the many features which make up an object or a concept is an incredible
data compression.  This may be why the gradual increase in computational
ability across primate evolution is not a very satisfying explanation for
the quantum leap in human intellectual ability.  Many of the explanations
of the origin of consciousness rely on the advantages of language for
improving analytic ability.  The one I like best is Julian Jaynes idea
(The Origin of Consciousness in the Breakdown of the Bicameral Mind):
that consciousness is not just a simple consequence of language, but
that the exponential growth in knowledge fostered by language generates
self-consciousness only after certain kinds of concepts are introduced
into language.  This allows him to trace the evolution of consciousness
by literary analysis!

Rich Goldschmidt    -- a former brain hacker (now reformed?)
cbosgd!rbg