Abstract: Pulse trains are utilized for the transmission of information in a neural network. A squash function is achieved by logically OR'ing together pulsed outputs, giving f(x) approximately 1-e.sup.-x. For Back Propagation, as derived by Rumelhart, the derivative of the squash function is available by examining the time when no OR'ed together pulses are present, being 1-f(x), or e.sup.-x. Logically AND'ing of the two signals. Mulitplication of input frequencies by weights is accomplished by modulating the width of the output pulses, while keeping the frequency the same.