1. An artificial asynchronous neural network system comprising a plurality of neurons each of which is operable to receive a respective input signal representing an input stimulus for the network, and to generate an output signal in response to receipt of such an input stimulus, the network system having a fixed predetermined physical configuration and being operable to supply output signals representing respective spatio-temporal sequences of rhythmic electric pulses to an external system in response to receipt of such input stimuli, each combination of such input stimuli generating a respective output signal, wherein said neurons are composed of respective pairs of differential CMOS transistors, wherein respective pairs of the multiple neurons are interconnected using mutually inhibitory links with asymmetric conductances, each link providing a synapse and formed using a differential current amplifier, the neurons and mutually inhibitory links forming the fixed predetermined physical configuration of the network system, which configuration is independent of received input signals.