Electronic simulation of an associative neuron

Abstract

In this thesis the various characteristics of a neuron are discussed at some length. Particular attention is given to the more important features which determine the input and output characteristics and the responses of a neuron. Included are both of the major inhibition characteristics: presynaptic inhibition (depolarization), and postsynaptic inhibition (hyperpolarization).

The simulation presented uses a single 12 volt power supply, operates on pulses which swing in the negative direction, has a high input impedance and a low output impedance, may be easily modified to adjust the response characteristics to individual system needs, and uses only 132 milliwatts power. Input pulses are weighted and transmitted to the summation circuit by a common collector stage which provides isolation of the inputs from the summation circuitry. A hyperpolarization input raises the resting voltage at the summation circuit, requiring more stimulation to lower the summation voltage to the threshold value. This inhibition follows a predetermined time course, The simulation will produce output pulses as long as the voltage at the summation circuit is below the threshold value. These pulses have a duration of 0.7 ms. and are followed by a refractory period of about one millisecond. A depolarization input lowers the amplitude of the output pulse by a predetermined time course.