They use analog building blocks, not digital ones: "Mead succeeded in mimicking ion-flow across a neuron's membrane with electron-flow through a transistor's c

They use analog building blocks, not digital ones: "Mead succeeded in mimicking ion-flow across a neuron's membrane with electron-flow through a transistor's channel. This should not have come as a surprise: the same physical forces are at work in both cases! A silicon neuron is an analog electronic circuit of transistors that mimic a real neuron's repertoire of ion-channels. Instead of designing different electronic circuits to emulate each of a wide variety of ion-selective protein pores that stud neurons' membranes, as Mead did in his silicon retina, we came up with a versatile silicon model." http://www.stanford.edu/group/brainsinsilicon/about.html http://www.stanford.edu/group/brainsinsilicon/about.html