The maximum likelihood approach to the identification of neuronal firing systems

The concern of this work is the identification of the (nonlinear) system of a neuron firing under the influence of a continuous input in one case, and firing under the influence of two other neurons in a second case. In the first case, suppose that the data consist of sample values Xt, Yt, t = 0, +/- 1, +/- 2,... with Yt = 1 if the neuron fires in the time interval t to t + 1 and Yt = 0 otherwise, and with Xt denoting the (sampled) noise value at time t. Suppose that Ht denotes the history of the process to time t. Then, in this case the model fit has the form Prob[Yt = 1/Ht] = phi(Ut-theta) where (formula; see text) where gamma t denotes the time elapsed since the neuron last fired and phi denotes the normal cumulative. This model corresponds to quadratic summation of the stimulus followed by a random threshold device. In the second case, a network of three neurons is studied and it is supposed that (formula; see text) with Xt and Zt zero-one series corresponding to the firing times of the two other neurons. The models are fit by the method of maximum likelihood to Aplysia californica data collected in the laboratory of Professor J.P. Segundo. The paper also contains some general comments of the advantages of the maximum likelihood method for the identification of nonlinear systems.