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Figure 4.7.
interconnected circuit of neurons. source: w. r. ashby,
Design for a
Brain
(london: chapman & Hall, 1952), 128, fig. 10/5/1. (with kind permission from
springer science and business media.)
protein solutions, enzyme systems, concentrations of hydrogen and other
ions, oxidation-reduction potentials, adsorbed layers, and many other con-
stituents or processes might act as step-mechanisms” (1952, 125). A second
suggestion is that neurons are “amoeboid, so that their processes could make
or break contact with other cells” (126). And third, Ashby reviews an idea he
associates with Rafael Lorente de Nó and Warren McCulloch, that the brain
contains interconnected circuits of neurons (fig. 4.7),
on which he observes
that “a simple circuit, if excited, would tend either to sink back to zero excita-
tion, if the amplification factor was less than unity, or to rise to the maximal
excitation if it was greater than unity.” Such a circuit would thus jump dis-
continuously from one state to another and “its critical states would be the
smallest excitation capable of raising it to full activity, and the smallest inhibi-
tion capable of stopping it” (128). Here, then, were three suggestions for the
go of it—plausible biological mechanisms that might account for the brain's
homeostatic adaptability.
The homeostat appears midway through
Design for a Brain
. The preceding
chapters prepare the way for it. Then its properties are reviewed. And then,
in the topic's concluding chapters, Ashby looks toward the future. “My aim,”
he says, with a strange kind of modesty, “is simply to copy the living brain”
(1952, 130). Clearly, a single homeostat was hardly comparable in its abilities
to the brain of a simple organism, never mind the human brain—it was “too
larval” (Ashby 1948, 343)—and the obvious next step was to contemplate a
multiplication of such units. Perhaps the brain was made up of a large number
of ultrastable units, biological homeostats. And the question Ashby then asked
was one of speed or efficiency: how long would it take such an assembly to
come into equilibrium with its environment?
