X-Message-Number: 3863
From:  (Joseph J. Strout)
Subject: SCI.CRYONICS Re: Uploading
Date: Fri, 17 Feb 1995 09:15:30 -0800 (PST)

> From: John K Clark <>
> Joseph J. Strout   Wrote: 

> 	   >the most basic signals in a neuron spread electrotonically,
> 	   >i.e. at the speed of light.
> 	   
> Electromagnetic interactions occur at the speed of light in
> neurons just as they do in all matter, even rocks, but their not
> signals unless they convey information. 

And they do!  I should have been more explicit about the signals I was
talking about.  Synapses (chemical or electric) cause a change in the
voltage of the membrane of the postsynaptic cell -- *locally* -- and
this voltage change spreads electrotonically over the cell.  This is
how synaptic inputs are integrated over space (i.e., from their
various sites around the neuron), resulting in some combined voltage
at the axon hillock, many microns away, which (mostly) determines
whether or not an action potential is fired.  These electrical signals
are crucial to the function of the cell, and act at lightspeed over
fairly large (on a cellular scale) distances.  Moreover, they are
critically dependent on the geometry of the cell (e.g., branch points,
dendritic spines, etc.), which is why uploading appears to require
determining cellular morphology to very high resolution...

Anyway, to speed up the entire system, as you suggest, you will have
to either have signals which travel faster than light, reduce the
scale of the system proportionately, or come up with some shortcuts
which you can compute faster than electrical potentials can integrate.
The first is clearly implausible, and the latter two would probably
produce only mild increases in speed.  5 or 10 times faster I might
believe, but billions?  It seems unlikely.

Joe Strout             Neuroscience, UCSD            

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