Although many researchers talk about modelling neural processes, there is a class of cell that greatly outnumbers the neurons in the brain. Amid some 10 10 neurons - leading some to conclude that you could store the brain's contents on a moderately large hard drive - there are some 10 15 synapses, which link the neurons together, to deal with. This is where modelling the neural structure in silicon is tricky. The neuron is a bit like a logic gate but the fan-in and fan-out is something we are not used to. It is on the order of a thousand to one.