X-Message-Number: 12628
Date: Sun, 24 Oct 1999 13:27:42 EDT
Subject: neuron info density

A couple of recent posts have commented on the paper in the Oct. 1, 1999 
issue of SCIENCE by Dodt et al, concerning the density of information storage 
on the surfaces of individual neurons. The pessimistic inference by the 
posters was that information storage, perhaps including memories, is much 
finer-grained than previously thought, and therefore much more easily lost.

The first poster (Leitl) reported the resolution of the scan as one "m m" 
which I took to mean micro-meter or micron, one millionth of a meter. I 
pointed out that a cubic micron contains a billion cubic nanometers, so on 
the scale of nanotechnology these would be very large structures, which tends 
toward optimism. 

The second poster (Darwin) said the resolution is 10 nanometers, ten nm. 

I have now printed out the full text of the paper from SCIENCE.  The 
following quotations are relevant to the question of resolution:

"A burst of light flashes caused an LTD like depression of glutamate receptor 
responses, which was highly confined to the region of 'tetanic' stimulation 
(<10 micrometers)."

"We were able to direct a [one micron] UV spot under visual control on the 
surface of the neuron being studied."

"The accuracy obtained was 4 [plus or minus] 1 [microns] laterally......and 
18 [plus or minus 2] [microns] axially....Thus, the effective 'glutamate 
release site' can be regarded roughly as a spot of 10 [micron] 
diameter.....Thus, the LTD observed iln our experiments had a spatial 
specificity of at least 10 [microns or micro-meters]. The actual extension of 
LTD may be even smaller, as the accuracy of the method is limited to the 10 
[micron] range."

We also know that the wave length of ultra violet light is of the order of 10 
microns, and ordinarily the resolution limit is of the same order as the wave 
length. (Actually, I have always thought that, by using different angles of 
attack and computer enhancement, one could get much better resolution, in 

So Leitl was right in his figures, and I was right, and Darwin was off by a 
factor of a thousand.

None of this is conclusive, of course, in either direction. But surely a 
pessimistic conclusion is particularly unwarranted.

Robert Ettinger
Cryonics Institute
Immortalist Society

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