Hand simulations of the action of this type of model suggest that a certain amount of randomness would be desirable. It appears that a self-organizing system built of these elements, and of sufficient complexity to be interesting, would have a fair number of recirculating loops, so that spontaneous activity would be maintained in the absence of input stimulus. If this is the case, then randomness could easily be introduced by adding a small amount of noise from a random noise generator to the signal on the P-R bus. Thus, any neurons which spontaneously fire would be continually having their thresholds modified. The mechanization of the model is not particularly complex, and can be estimated as follows: The one-shot pulse generator would require two transistors, the pulse stretcher one more. The bi-directional gate would require a transistor and at least two diodes. Several candidates for the electrically-controllable variable resistor are available (6). Particularly good candidates appear to be the “Memistor” or plating cell developed by Widrow (7), the solid state version of it by Vendelin (8), and the “solion” (9). All are electrochemical devices in which the resistance between two terminals is controlled by the net charge flow through a third terminal. All are adaptable to this particular circuit. Of the three, however, the solion appears at first glance to have the most promise in that its resistance is of the order of a few thousand ohms (rather than the few ohms of the plating cells) which is more compatible with ordinary solid-state circuitry. Solions have the disadvantage that they can stand only very low voltages (less than 1 volt) and in their present form require extra bias potentials. If these difficulties can be overcome, they offer considerable promise. In summary, it appears that a rather simple neuron model can be built which can mimic most of the important functions of real neurons. A system built of these could be punished or rewarded by an observer, so that it could be trained to give specified responses to specified stimuli. In some cases, the observer could be simply the environment, so that the system would learn directly from experience, and would be therefore a self-organizing system. REFERENCES 1. Hodgkin, A. L., and Huxley, A. L., “A Quantitative Description of Membrane Current and its Application to Conduction and Excitation in Nerve,” _J. Physiol._ =117=:500-544 (August 1952) 2. Crane, H. D., “Neuristor—A Novel Device and System Concept,” _Proc. IRE_ =50=:2048-2060 (Oct. 1962) 3. Harmon, L. D., Levinson, J., and Van Bergeijk, W. A., “Analog Models of Neural Mechanism,” _IRE Trans. on Information Theory_ =IT-8=:107-112 (Feb. 1962) 4. Widrow, B., and Hoff, M. E., “Adaptive Switching Circuits,” Stanford Electronics Lab Tech Report 1553-1, June 1960