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FIGURE 28. Net detecting right hand edges, and right hand edges moving to the right
(a). Formal presentation. (b) Simplest equivalent neural net.
works as they occur at the thalamic relay nucleus with the somatic system
as input.
3.7. Action Networks of Cell Assemblies
Sholl (1956) estimates the mean density ¯ of neurons in the human cortex
at about 10 7 neurons per cubic centimeter, although this number may var y
considerably from region to region. This density implies a mean distance
from neuron to neuron.
l
1
3
-
= ()
l
v
510cm
-
3
or approximately 50 m. This distance corresponds, of course, to the lattice
constants D x , D y , D z , etc. in the previous paragraph and gives the elemen-
tary lattice cell a volume of D x D y D z ª 10 -7 cm 3 . Even with the best equip-
ment available today we cannot reproducibly attain a given point in the
brain within this range. Consequently, our cell by cell approach describes a
highly idealistic situation, and the question arises as to whether or not some
of the earlier concepts can be saved if we wish to apply them to a much
more realistic situation.
Let us assume optimistically that one is able to locate a certain point in
the living cortex within, say 0.5 mm = 500 m. This defines a volume of uncer-
tainty which contains approximately a thousand neurons. This number, on
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