Neural representation of the acoustic biotope: On the existence of stimulus-event relations for sensory neurons

Abstract

In the context of a behaviourally oriented investigation of neural information processing we have studied single unit responses from cochlear nucleus (12 units) and auditory cortex (23 units) of the cat. Attention was focused on two aspects: the composition of a wide stimulus ensemble and the influence of this ensemble on the single unit neural activity: action potentials or neural events. The stimulus ensemble was based on sounds occurring in the natural environment of the animal: the Acoustic Biotope. A realization of such an ensemble was constructed and used in the experiments. A systematic analysis of the effect of this stimulus ensemble on the neural activity comprises different questions with respect to a possible stimulus-event relation: existence and nature. In the present paper emphasis is given to the question of existence of a s-e relation. The existence of such a relation has been investigated by presenting the stimulus ensemble twice. The degree of reproducibility of neural activity indicates to what extent a s-e relation indeed exists. A formal measure of testing the reproducibility of two sequences of neural events is defined: the Cross Coincidence Function. Results are presented, interpretation and formal problems discussed. Results obtained so far indicate that on the whole the existence of a s-e relation can be established more definitely for cochlear nucleus units than for auditory cortex units. Applications of the presented procedure arise in exploratory investigations in central regions of the sensory nervous system and in regions with presumed multimodal inputs.