Pigeon Spontaneous and Evoked Activities - a Renewal Process?

Spontaneous activities of pigeon auditory nerve fibres were tested for a renewal process. The experiments falsified mutually statistically independent lengths of time intervals between successive actions potentials. However, the generation of action potentials on the eighth nerve by a complex system as the inner ear might not be described by a simple renewal process. The superposition of many different stochastic processes are conceivable in composed systems as the ear. Therefore, spontaneous activities have been described in the present experiments by a doubly embedded stochastic model, the Hidden Markov Model. The model is composed of hidden and observable states. These different hidden states generate with different probabilities the action potentials (observable states) on the auditory nerve. In addition to spontaneous activities, responses of pigeon auditory nerve fibres to white noise stimuli have been evaluated to investigate signal transduction. Wiener kernels have been identified by fast orthogonal search. The results suggest that nonlinearities are only instantaneous and that the investigated acoustically evoked neuronal activities might be described by cascades of linear and static nonlinear devices. Considerable improvements are possible by generalisation of the ordinary Wiener series, so that prior neuronal activity can be taken into account. Recorded inter-spike-interval distributions and rate-intensity functions can be described by a stochastic model derived from extended functional series.