[Risk functions and expected spike density functions for neurons in the cat cochlear nucleus]

The temporal properties of spontaneous and (or) evoked discharges of 157 neurons localized in dorsal cochlear nucleus of anaesthetized cats have been studied. Tone bursts were presented at stimulus best frequency in a free field from the side of ipsilateral ear. About half of cells were characterized by paused or build-up types of the discharge. For all such units a long lasting post-spike decrease in excitability could be seen from the analysis of hazard functions of spontaneous and evoked activity. As a result, the time dependence of conditional probability of the first crossing of the threshold (under condition of an absence of previous response spikes) or expecting probability function (EPF) were over the usual peristimulus histograms. Units with chopper discharges usually did not demonstrate alternative peaks in EPF. We interpreted this fact as evidence that chopper discharge pattern is a result of strong post spike decrease in excitability. Such pattern doesn't demonstrate an existence of real periodicity of the unit. In primary-like units the hazard functions demonstrated only minor after-spike decrease of excitability, and the EPFs were similar to the initial part of peristimulus histograms. Type II units (presumably inhibitory cells) were characterized by non-monotonous hazard functions and by a tendency to burst response patterns. In some cells, we observed a tendency to existence of real intrinsic oscillations both in the EPFs and hazard functions.