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From: ins_atge@jhunix.HCF.JHU.EDU (Thomas G Edwards)
Newsgroups: comp.ai
Subject: Re: How much info can the brain hold?
Summary: Neurons
Message-ID: <7034@jhunix.HCF.JHU.EDU>
Date: 30 Nov 90 20:45:36 GMT
References: <11941@hubcap.clemson.edu> <7492@hub.ucsb.edu>
Organization: The Johns Hopkins University - HCF
Lines: 40

In article <7492@hub.ucsb.edu> 6600dt@ucsbuxa.ucsb.edu (Dave Goggin) writes:
>I'd follow up with another questin of brain
>computer comparison.  It is known that much of the
>brain's power comes ffom the high degree of
>paraallel processing involved.  What is the speed
>(in MHz, or other units) that the brin runs at, and
>how does it vary with state.  Also, how does this
>compare iwht existing parrallel-processed hardware?

The brain wins on number of processing units when compared to existing
parallel machines (such as the Connection Machine with only 64K
processors).  This would be even if you only count neurons, and
not glial cells and other support mechanisms which could play some
unknown cognitive roles.

Most neurons fire at less than 100 Hz.  But, there is a large question
of whether individual pulses really mean anything by themselves
in all of brain.  While there is some indication that while in some places
in brain a single pulse might be meaningful, some of brain probably works
frequency and phase modulation of pulse trains.  One aspect which
has been looked into is synchronous firing of neurons associated
with different parts of the same object in the visual field.
This type of "phase-locking attentional mechanisms" may explain
why there are limits to some kinds of short-term memory (like
how long a train of digits you can repeat back to me if I tell them
to you, or maximum number of individually tracked objects in
visual field) due to a limited amount of "phase slots" into which
these attended stimuli can fit.

Secondly, alot more goes on in neurons than action potentials.
For example, long-term potentiation is going on, something which doesn't
easily translate into a clock speed.  Also there are much slower
DC potentials working across cells.

And thridly neurons have fairly large connectivity (up to about 10,000)
which is a few orders of magnitude greater than the connectivity of
your average processor in a parallel machine (I guess no more than 32
if you are in a hypercube).

-Tom