1. A neuron network comprising interconnected input, hidden and output layers of neurons, said neurons comprising "on-off" or threshold electronic devices, all of said neurons which are connected being symmetrically connected by means of automatically-adjustable synapse pairs, each of said synapses comprises a plurality of drain-source circuits of field effect transistors, said source-drain circuits having resistances or conductances which differ from each other by ratios of 2 to 1, whereby different combinations of said source-drain circuits can be switched in parallel to provide any resistance or conductance, in a binary sequence, for each of said synapses, said synapses being controlled by the output of an Up-Down counter, and means to control the reading of said counter depending on the results of a correlation of the states of each connected pair of said neurons following the application of sets of training signals to said neurons network.